WebWhen producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing WebQuestia. After more than twenty years, Questia is discontinuing operations as of Monday, December 21, Web2 days ago · Free source code and tutorials for Software developers and Architects blogger.com allows expert authors in hundreds of niche fields to get massive levels of exposure in exchange for the submission of their quality original articles WebThis Windows operational tutorial covers the benefits and all the steps to consider when moving to cloud-based group policies and other configurations. If you are trying to figure out how to apply group policies on and off the domain, enforce those policies offline, track compliance, use inbox or application AMDX policies, and don’t know where to start in ... read more
Mobile phones with PMP functionalities such as video playback also started appearing in the s. Other non-phone products such as the PlayStation Portable and PlayStation Vita have also been considered to be PMPs.
DAPs and PMPs have declined in popularity after the late s due to increasing worldwide adoption of smartphones that already come with PMP functionalities.
In the EU , demand for MP3 players peaked in with Both sales and revenue experienced a double-digit shrinkage for the first time in Meanwhile, sales of the best selling product, the iPod, was eclipsed by the company's iPhone smartphone by DAPs continue to be made in lower volumes by manufacturers such as SanDisk, Sony, IRIVER, Philips, Apple, Cowon, and a range of Chinese manufacturers namely Aigo, Newsmy, PYLE and ONDA.
Usually, a colour liquid crystal display LCD or organic light-emitting diode OLED screen is used as a display for PMPs that have a screen. Various players include the ability to record video, usually with the aid of optional accessories or cables, and audio, with a built-in microphone or from a line out cable or FM tuner. Some players include readers for memory cards , which are advertised to equip players with extra storage or transferring media. In some players, features of a personal organiser are emulated, or support for video games , like the iriver clix through compatibility of Adobe Flash Lite or the PlayStation Portable , is included.
Only mid-range to high-end players support "savestating" for power-off i. Nearly all players  [ failed verification ] are compatible with the MP3 audio format, and many others support Windows Media Audio WMA , Advanced Audio Coding AAC and WAV. Some players are compatible with open-source formats like Ogg Vorbis and the Free Lossless Audio Codec FLAC.
Audio files purchased from online stores may include digital rights management DRM copy protection, which many modern players support. The JPEG format is widely supported by players.
Some players, like the iPod series, provide compatibility to display additional file formats like GIF , PNG , and TIFF , while others are bundled with conversion software. Most newer players support the MPEG-4 Part 2 video format, and many other players are compatible with Windows Media Video WMV and AVI. Software included with the players may be able to convert video files into a compatible format. Many players have a built-in electret microphone which allows recording. Usually recording quality is poor, suitable for speech but not music.
There are also professional-quality recorders suitable for high-quality music recording with external microphones, at prices starting at a few hundred dollars. Some DAPs have FM radio tuners built in. Many also have an option to change the band from the usual DAPs typically never have an AM band, or even HD Radio since such features would be either cost-prohibitive for the application, or because of AM's sensitivity to interference. Newer portable media players are now coming with Internet access via Wi-Fi.
Examples of such devices are Android OS devices by various manufacturers, and iOS devices on Apple products like the iPhone , iPod Touch , and iPad. Internet access has even enabled people to use the Internet as an underlying communications layer for their choice of music for automated music randomisation services like Pandora , to on-demand video access which also has music available such as YouTube. This technology has enabled casual and hobbyist DJs to cue their tracks from a smaller package from an Internet connection, sometimes they will use two identical devices on a crossfade mixer.
Many such devices also tend to be smartphones. Many mobile digital media players have last position memory , in which when it is powered off, a user doesn't have to worry about starting at the first track again, or even hearing repeats of others songs when a playlist, album, or whole library is cued for shuffle play , in which shuffle play is a common feature, too. Early playback devices to even remotely have "last position memory" that predated solid-state digital media playback devices were tape-based media, except this kind suffered from having to be "rewound", whereas disc-based media suffered from no native "last position memory", unless disc-players had their own last position memory.
However, some models of solid-state flash memory or hard drive ones with some moving parts are somewhat the "best of both worlds" in the market. Media players' firmware may be equipped with a basic file manager and a text reader. There are also royalty free lossy formats like Vorbis for general music and Speex and Opus used for voice recordings.
When "ripping" music from CDs, many people recommend the use of lossless audio formats to preserve the CD quality in audio files on a desktop, and to transcode the music to lossy compression formats when they are copied to a portable player.
MP3 and AAC are dominant formats,  and are almost universally supported. For later players, however, these are usually available online via the manufacturers' websites, or increasingly natively recognised by the operating system through Universal Mass Storage UMS or Media Transfer Protocol MTP. As with DAPs, PMPs come in either flash or hard disk storage. Storage capacities have reached up to 64 GB for flash memory based PMPs, first reached by the 3rd Generation iPod Touch , and up to 1 TB for hard disk drive PMPs, first achieved by the Archos 5 Internet Tablet.
A number of players support memory card slots, including CompactFlash CF , Secure Digital SD , and Memory Sticks. They are used to directly transfer content from external devices, and expand the storage capacity of PMPs.
A standard PMP uses a 5-way D-pad to navigate. Many alternatives have been used, most notably the wheel and touch mechanisms seen on players from the iPod and Sansa series.
Another popular mechanism is the swipe-pad, or 'squircle', first seen on the Zune. Additional buttons are commonly seen for features such as volume control. Sizes range all the way up to 7 inches 18 cm. Resolutions also vary, going up to WVGA. Most screens come with a colour depth of bit, but higher quality video-oriented devices may range all the way to bit, otherwise known as true colour , with the ability to display Screens commonly have a matte finish but may also come in glossy to increase colour intensity and contrast.
More and more devices are now also coming with touch screen as a form of primary or alternate input. Certain devices, on the other hand, have no screen whatsoever, reducing costs at the expense of ease of browsing through the media library.
Some portable media players include a radio receiver , most frequently receiving FM. Features for receiving signals from FM stations on MP3 players are common on more premium models. Some portable media players have recently added features such as simple camera, built-in game emulation playing Nintendo Entertainment System or other game formats from ROM images and simple text readers and editors. Newer PMPs have been able to tell time, and even automatically adjust time according to radio reception, and some devices like the 6th-gen iPod Nano even have wristwatch bands available.
Modern MP4 players can play video in a multitude of video formats without the need to pre-convert them or downsize them prior to playing them. Some MP4 Players possess USB ports, to allow users to connect it to a personal computer to sideload files. Some models also have memory card slots to expand the memory of the player instead of storing files in the built-in memory.
The image compression algorithm of this format  is inefficient by modern standards about 4 pixels per byte, compared with over 10 pixels per byte for MPEG There are a fixed range of resolutions 96 × 96 to × pixels and framerates 12 or 16 frames available.
A minute video would have a filesize of approximately MB at a × resolution. The MTV video format no relation to the cable network consists of a byte file header that operates by displaying a series of raw image frames during MP3 playback.
This method does not require additional hardware for decoding, though it will lead to a higher amount of memory consumption. For that reason, the storage capacity of an MP4 player that uses MTV files is effectively less than that of a player that decompresses files on the fly.
Digital sampling is used to convert an audio wave to a sequence of binary numbers that can be stored in a digital format, such as MP3.
Common features of all MP3 players are a memory storage device, such as flash memory or a miniature hard disk drive , an embedded processor , and an audio codec microchip to convert the compressed file into an analogue sound signal. During playback, audio files are read from storage into a RAM based memory buffer, and then streamed through an audio codec to produce decoded PCM audio. Typically audio formats decode at double to more than 20 times real speed on portable electronic processors ,  requiring that the codec output be stored for a time until the DAC can play it.
To save power, portable devices may spend much or nearly all of their time in a low power idle state while waiting for the DAC to deplete the output PCM buffer before briefly powering up to decode additional audio.
Most DAPs are powered by rechargeable batteries , some of which are not user-replaceable. They have a 3. Some devices also contain internal speakers, through which music can be listened to, although these built-in speakers are typically of very low quality.
Nearly all DAPs consists of some kind of display screen, although there are exceptions, such as the iPod Shuffle , and a set of controls with which the user can browse through the library of music contained in the device, select a track, and play it back.
The display, if the unit even has one, can be anything from a simple one or two line monochrome LCD display, similar to what are found on typical pocket calculators , to large, high-resolution, full-color displays capable of displaying photographs or viewing video content on.
One of the more common methods of control is some type of the scroll wheel with associated buttons. This method of control was first introduced with the Apple iPod and many other manufacturers have created variants of this control scheme for their respective devices. Content is placed on DAPs typically through a process called "syncing", by connecting the device to a personal computer, typically via USB , and running any special software that is often provided with the DAP on a CD-ROM included with the device, or downloaded from the manufacturer's website.
Some devices simply appear as an additional disk drive on the host computer, to which music files are simply copied like any other type of file. Other devices, most notably the Apple iPod or Microsoft Zune , requires the use of special management software, such as iTunes or Zune Software, respectively. The music, or other content such as TV episodes or movies, is added to the software to create a "library". The library is then "synced" to the DAP via the software.
The software typically provides options for managing situations when the library is too large to fit on the device being synced to. Such options include allowing manual syncing, in that the user can manually "drag-n-drop" the desired tracks to the device, or allow for the creation of playlists. In addition to the USB connection, some of the more advanced units are now starting to allow syncing through a wireless connection, such as via Wi-Fi or Bluetooth.
Content can also be obtained and placed on some DAPs, such as the iPod Touch or Zune HD by allowing access to a "store" or "marketplace", most notably the iTunes Store or Zune Marketplace , from which content, such as music and video, and even games, can be purchased and downloaded directly to the device.
A growing number of portable media players are including audio processing chips that allow digital effects like 3D audio effects , dynamic range compression and equalisation of the frequency response. Some media players are used with Noise-cancelling headphones that use Active noise reduction to remove background noise.
De-noise mode is an alternative to Active noise reduction. It provides for relatively noise-free listening to audio in a noisy environment. In this mode, audio intelligibility is improved due to selective gain reduction of the ambient noise. This method splits external signals into frequency components by "filterbank" according to the peculiarities of human perception of specific frequencies and processing them using adaptive audio compressors.
Operation thresholds in adaptive audio compressors in contrast to "ordinary" compressors are regulated depending on ambient noise levels for each specific bandwidth. Reshaping of the processed signal from adaptive compressor outputs is realised in a synthesis filterbank. This method improves the intelligibility of speech signals and music. The best effect is obtained while listening to audio in the environment with constant noise in trains, automobiles, planes , or in environments with fluctuating noise level e.
in a metro. Improvement of signal intelligibility in condition of ambient noise allows users to hear audio well and preserve hearing ability, in contrast to regular volume amplification. Natural mode is characterised by subjective effect of balance of different frequency sounds, regardless of level of distortion, appearing in the reproduction device.
It is also regardless of personal user's ability to perceive specific sound frequencies excluding obvious hearing loss. The natural effect is obtained due to special sound processing algorithm i. Its principle is to assess frequency response function FRF of mediaplayer or any other sound reproduction device, in accordance with audibility threshold in silence subjective for each person ,  and to apply gain modifying factor.
The factor is determined with the help of integrated function to test audibility threshold: the program generates tone signals with divergent oscillations — from minimum volume 30—45 Hz to maximum volume appr. The principle is similar to in situ audiometry , used in medicine to prescribe a hearing aid. However, the results of test may be used to a limited extent as far as FRF of sound devices depends on reproduction volume. It means correction coefficient should be determined several times — for various signal strengths, which is not a particular problem from a practical standpoint.
Sound around mode allows for real time overlapping of music and the sounds surrounding the listener in their environment, which are captured by a microphone and mixed into the audio signal. As a result, the user may hear playing music and external sounds of the environment at the same time. This can increase user safety especially in big cities and busy streets , as a user can hear a mugger following them or hear an oncoming car. Although these issues are not usually controversial within digital audio players, they are matters of continuing controversy and litigation, including but not limited to content distribution and protection, and digital rights management DRM.
The Recording Industry Association of America RIAA filed a lawsuit in late against Diamond Multimedia for its Rio players,   alleging that the device encouraged copying music illegally.
But Diamond won a legal victory on the shoulders of the Sony Corp. Universal City Studios case and DAPs were legally ruled as electronic devices. According to the Scientific Committee on Emerging and Newly Identified Health Risks , the risk of hearing damage from digital audio players depends on both sound level and listening time.
The listening habits of most users are unlikely to cause hearing loss, but some people are putting their hearing at risk, because they set the volume control very high or listen to music at high levels for many hours per day. Such listening habits may result in temporary or permanent hearing loss, tinnitus , and difficulties understanding speech in noisy environments.
The World Health Organization warns that increasing use of headphones and earphones puts 1. The World Health Organization recommends that "the highest permissible level of noise exposure in the workplace is 85 dB up to a maximum of eight hours per day" and time in "nightclubs, bars and sporting events" should be limited because they can expose patrons to noise levels of dB.
The report states. They can also limit the time spent engaged in noisy activities by taking short listening breaks and restricting the daily use of personal audio devices to less than one hour. With the help of smartphone apps, they can monitor safe listening levels. The report also recommends that governments raise awareness of hearing loss, and to recommend people visit a hearing specialist if they experience symptoms of hearing loss, which include pain, ringing or buzzing in the ears.
This growing phenomena has led to the coining of the term music-induced hearing loss, which includes hearing loss as a result of overexposure to music on personal media players. Some MP3 players have electromagnet transmitters, as well as receivers. Many MP3 players have built-in FM radios, but FM transmitters aren't usually built-in due to liability of transmitter feedback from simultaneous transmission and reception of FM.
Also, certain features like Wi-Fi and Bluetooth can interfere with professional-grade communications systems such as aircraft at airports. From Wikipedia, the free encyclopedia.
Portable device capable of storing and playing digital media. Not to be confused with Digital media player. Two flash memory type pocket-size PMPs: Sony 's Walkman A and Apple 's iPod Nano late s.
A larger sized, hard disk memory type PMP: the Archos s. A small DAP: the SanDisk Clip Jam s. See also: Portable audio player. Two early DAPs from FlashPAC and Listen Up. This section may require cleanup to meet Wikipedia's quality standards. The specific problem is: too long and confusing, needs subheadings. Please help improve this section if you can.
April Learn how and when to remove this template message. Main article: Last position memory. This section needs expansion with: Information about the architecture, processor, chipset, etc.
You can help by adding to it. December Main article: AMV video format. Further information: iTunes Store § The Consumer Council of Norway EULA challenge , and Digital rights management. Main article: Recording Industry Ass'n of America v. Diamond Multimedia Systems, Inc. Comparison of portable media players Digital video recorder Internet radio device Mixtape Notel Portable DVD player Walkman Circ. Archived from the original on 10 September GNU Operating System.
Free Software Foundation, Inc. Archived from the original on 3 June Retrieved 8 July Most support the patented MP3 codec, but not all.
To call such players 'MP3 players' is not only confusing, We suggest the terms 'digital audio player,' or simply 'audio player' if context permits. Retrieved 16 August Retrieved 19 April Tom's Hardware. EE Times Asia. Archived from the original on 23 April Retrieved 3 October The Guardian. Archived from the original on 6 April Retrieved 9 April Retrieved 9 June Archived from the original on 18 February Encyclopedia of Consumer Culture.
SAGE Publishing. ISBN Archived from the original on 27 May Archived PDF from the original on 29 December Retrieved 29 December Archived from the original on 27 March Archived from the original on 29 December se in Swedish.
Archived from the original on 13 April Retrieved 8 May Archived from the original on 20 October Retrieved 8 May — via content. Johnston, D. Sinha, S. Dorward, and S. Gilchrist and C. Johnston, J. Herre, M. Davis, and U. Consumer Devices for Networked Audio. Proceedings of the IEEE International Symposium on Industrial Electronics. CNN Business Week 7 March Archived from the original on 10 May Archived from the original on 18 January Retrieved 20 February University of Utah.
Retrieved 14 July Roberto Verganti, Design-Driven Innovation: Changing the Rules of Competition by Radically Innovating What Thing Mean. Harvard Business Press, Archived from the original on 18 October Archived from the original on 31 December Archived from the original on 21 January The Register.
Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a different name. The optimization works more effectively with link-time optimization enabled. If a function is patched, its impacted functions should be patched too. Usually, the more IPA optimizations enabled, the larger the number of impacted functions for each function. In order to control the number of impacted functions and more easily compute the list of impacted function, IPA optimizations can be partially enabled at two different levels.
Only enable inlining and cloning optimizations, which includes inlining, cloning, interprocedural scalar replacement of aggregates and partial inlining.
Only enable inlining of static functions. As a result, when patching a static function, all its callers are impacted and so need to be patched as well. When -flive-patching is specified without any value, the default value is inline-clone. Note that -flive-patching is not supported with link-time optimization -flto. Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer.
Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This flag is enabled by default at -O2 and higher and depends on -fdelete-null-pointer-checks also being enabled. This is not currently enabled, but may be enabled by -O2 in the future. Perform forward store motion on trees. Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information.
This pass only operates on local scalar variables and is enabled by default at -O1 and higher, except for -Og. It requires that -ftree-ccp is enabled. Perform sparse conditional constant propagation CCP on trees.
This pass only operates on local scalar variables and is enabled by default at -O1 and higher. Propagate information about uses of a value up the definition chain in order to simplify the definitions.
For example, this pass strips sign operations if the sign of a value never matters. The flag is enabled by default at -O1 and higher. Perform pattern matching on SSA PHI nodes to optimize conditional code. This pass is enabled by default at -O1 and higher, except for -Og. Perform conversion of simple initializations in a switch to initializations from a scalar array. Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping.
The compilation time in this pass can be limited using max-tail-merge-comparisons parameter and max-tail-merge-iterations parameter. Perform dead code elimination DCE on trees. Perform conditional dead code elimination DCE for calls to built-in functions that may set errno but are otherwise free of side effects.
This flag is enabled by default at -O2 and higher if -Os is not also specified. Assume that a loop with an exit will eventually take the exit and not loop indefinitely.
This allows the compiler to remove loops that otherwise have no side-effects, not considering eventual endless looping as such. This also performs jump threading to reduce jumps to jumps. Perform dead store elimination DSE on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations.
It also saves one jump. It is not enabled for -Os , since it usually increases code size. Perform loop optimizations on trees. Perform loop nest optimizations. Same as -floop-nest-optimize. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.
Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Some minimal optimizations are also performed by the code generator isl, like index splitting and dead code elimination in loops. Enable the isl based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms.
It calculates a loop structure optimized for data-locality and parallelism. This option is experimental. Use the Graphite data dependence analysis to identify loops that can be parallelized.
Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops. While transforming the program out of the SSA representation, attempt to reduce copying by coalescing versions of different user-defined variables, instead of just compiler temporaries.
This may severely limit the ability to debug an optimized program compiled with -fno-var-tracking-assignments. In the negated form, this flag prevents SSA coalescing of user variables. This option is enabled by default if optimization is enabled, and it does very little otherwise. Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops.
This is enabled by default if vectorization is enabled. Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop. Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O2 and higher, and by -fprofile-use and -fauto-profile.
This pass distributes the initialization loops and generates a call to memset zero. and the initialization loop is transformed into a call to memset zero. Perform loop interchange outside of graphite.
This flag can improve cache performance on loop nest and allow further loop optimizations, like vectorization, to take place. Apply unroll and jam transformations on feasible loops.
In a loop nest this unrolls the outer loop by some factor and fuses the resulting multiple inner loops. Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTL level function calls, operations that expand to nontrivial sequences of insns.
With -funswitch-loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion. Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling. Perform final value replacement.
If a variable is modified in a loop in such a way that its value when exiting the loop can be determined using only its initial value and the number of loop iterations, replace uses of the final value by such a computation, provided it is sufficiently cheap. This reduces data dependencies and may allow further simplifications. Perform induction variable optimizations strength reduction, induction variable merging and induction variable elimination on trees.
Parallelize loops, i. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e. by memory bandwidth. This option implies -pthread , and thus is only supported on targets that have support for -pthread. Perform function-local points-to analysis on trees.
This flag is enabled by default at -O1 and higher, except for -Og. Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. Perform merging of narrow stores to consecutive memory addresses.
This pass merges contiguous stores of immediate values narrower than a word into fewer wider stores to reduce the number of instructions. This is enabled by default at -O2 and higher as well as -Os.
This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation.
This is enabled by default at -O1 and higher. Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible.
Perform vectorization on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly specified. Perform loop vectorization on trees. This flag is enabled by default at -O2 and by -ftree-vectorize , -fprofile-use , and -fauto-profile. Perform basic block vectorization on trees.
Initialize automatic variables with either a pattern or with zeroes to increase the security and predictability of a program by preventing uninitialized memory disclosure and use. With this option, GCC will also initialize any padding of automatic variables that have structure or union types to zeroes. However, the current implementation cannot initialize automatic variables that are declared between the controlling expression and the first case of a switch statement.
Using -Wtrivial-auto-var-init to report all such cases. You can control this behavior for a specific variable by using the variable attribute uninitialized see Variable Attributes. Alter the cost model used for vectorization. Alter the cost model used for vectorization of loops marked with the OpenMP simd directive. All values of model have the same meaning as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used.
Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled. Split paths leading to loop backedges.
This can improve dead code elimination and common subexpression elimination. This is enabled by default at -O3 and above. Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration.
This breaks long dependency chains, thus improving efficiency of the scheduling passes. A combination of -fweb and CSE is often sufficient to obtain the same effect.
However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSE pass. With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code. Inline parts of functions. Perform predictive commoning optimization, i.
This option is enabled at level -O3. If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. Do not substitute constants for known return value of formatted output functions such as sprintf , snprintf , vsprintf , and vsnprintf but not printf of fprintf.
This transformation allows GCC to optimize or even eliminate branches based on the known return value of these functions called with arguments that are either constant, or whose values are known to be in a range that makes determining the exact return value possible. For example, when -fprintf-return-value is in effect, both the branch and the body of the if statement but not the call to snprint can be optimized away when i is a bit or smaller integer because the return value is guaranteed to be at most 8.
The -fprintf-return-value option relies on other optimizations and yields best results with -O2 and above. It works in tandem with the -Wformat-overflow and -Wformat-truncation options.
The -fprintf-return-value option is enabled by default. Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both.
GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback -fprofile-arcs. These heuristics are based on the control flow graph. The default is -fguess-branch-probability at levels -O , -O2 , -O3 , -Os.
Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. Use the specified algorithm for basic block reordering. In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and.
o files, to improve paging and cache locality performance. When -fsplit-stack is used this option is not enabled by default to avoid linker errors , but may be enabled explicitly if using a working linker.
Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections. hot for most frequently executed functions and. unlikely for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way.
Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same.
A character type may alias any other type. Even with -fstrict-aliasing , type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. See Structures unions enumerations and bit-fields implementation.
However, this code might not:. Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e. The -fstrict-aliasing option is enabled at levels -O2 , -O3 , -Os. Controls whether rules of -fstrict-aliasing are applied across function boundaries. Note that if multiple functions gets inlined into a single function the memory accesses are no longer considered to be crossing a function boundary.
The -fipa-strict-aliasing option is enabled by default and is effective only in combination with -fstrict-aliasing. Align the start of functions to the next power-of-two greater than or equal to n , skipping up to m -1 bytes. This ensures that at least the first m bytes of the function can be fetched by the CPU without crossing an n -byte alignment boundary.
If m2 is not specified, it defaults to n2. Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is If this option is enabled, the compiler tries to avoid unnecessarily overaligning functions.
It attempts to instruct the assembler to align by the amount specified by -falign-functions , but not to skip more bytes than the size of the function.
Parameters of this option are analogous to the -falign-functions option. If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead.
Align loops to a power-of-two boundary. If the loops are executed many times, this makes up for any execution of the dummy padding instructions. Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping.
In this case, no dummy operations need be executed. Allow the compiler to perform optimizations that may introduce new data races on stores, without proving that the variable cannot be concurrently accessed by other threads.
Does not affect optimization of local data. It is safe to use this option if it is known that global data will not be accessed by multiple threads. Examples of optimizations enabled by -fallow-store-data-races include hoisting or if-conversions that may cause a value that was already in memory to be re-written with that same value. Such re-writing is safe in a single threaded context but may be unsafe in a multi-threaded context. Note that on some processors, if-conversions may be required in order to enable vectorization.
This option is left for compatibility reasons. Do not reorder top-level functions, variables, and asm statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables are not removed. This option is intended to support existing code that relies on a particular ordering.
For new code, it is better to use attributes when possible. Additionally -fno-toplevel-reorder implies -fno-section-anchors. This also affects any such calls implicitly generated by the compiler. Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover.
Assume that the current compilation unit represents the whole program being compiled. This option should not be used in combination with -flto. Instead relying on a linker plugin should provide safer and more precise information. This option runs the standard link-time optimizer. When the object files are linked together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit.
To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. For example:. The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo.
o and bar. The final invocation reads the GIMPLE bytecode from foo. o , merges the two files into a single internal image, and compiles the result as usual. Since both foo. o are merged into a single image, this causes all the interprocedural analyses and optimizations in GCC to work across the two files as if they were a single one.
This means, for example, that the inliner is able to inline functions in bar. o into functions in foo. o and vice-versa. The above generates bytecode for foo. c and bar. c , merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog. The important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link step.
GCC automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You can always override the automatic decision to do link-time optimization by passing -fno-lto to the link command.
To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin see -fuse-linker-plugin passes information to the compiler about used and externally visible symbols.
When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions.
When a file is compiled with -flto without -fuse-linker-plugin , the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code see -ffat-lto-objects. This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied.
Note that when -fno-fat-lto-objects is enabled the compile stage is faster but you cannot perform a regular, non-LTO link on them. When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode.
Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing. Generally, options specified at link time override those specified at compile time, although in some cases GCC attempts to infer link-time options from the settings used to compile the input files.
If you do not specify an optimization level option -O at link time, then GCC uses the highest optimization level used when compiling the object files. Note that it is generally ineffective to specify an optimization level option only at link time and not at compile time, for two reasons.
First, compiling without optimization suppresses compiler passes that gather information needed for effective optimization at link time. Second, some early optimization passes can be performed only at compile time and not at link time. There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link. Currently, the following options and their settings are taken from the first object file that explicitly specifies them: -fcommon , -fexceptions , -fnon-call-exceptions , -fgnu-tm and all the -m target flags.
The following options -fPIC , -fpic , -fpie and -fPIE are combined based on the following scheme:. Certain ABI-changing flags are required to match in all compilation units, and trying to override this at link time with a conflicting value is ignored.
This includes options such as -freg-struct-return and -fpcc-struct-return. Other options such as -ffp-contract , -fno-strict-overflow , -fwrapv , -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting translation units. You can override them at link time. Diagnostic options such as -Wstringop-overflow are passed through to the link stage and their setting matches that of the compile-step at function granularity.
Note that this matters only for diagnostics emitted during optimization. Note that code transforms such as inlining can lead to warnings being enabled or disabled for regions if code not consistent with the setting at compile time. When you need to pass options to the assembler via -Wa or -Xassembler make sure to either compile such translation units with -fno-lto or consistently use the same assembler options on all translation units.
You can alternatively also specify assembler options at LTO link time. To enable debug info generation you need to supply -g at compile time. If any of the input files at link time were built with debug info generation enabled the link will enable debug info generation as well. Any elaborate debug info settings like the dwarf level -gdwarf-5 need to be explicitly repeated at the linker command line and mixing different settings in different translation units is discouraged.
If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together undefined behavior according to ISO C99 6. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages:.
In general, when mixing languages in LTO mode, you should use the same link command options as when mixing languages in a regular non-LTO compilation. If object files containing GIMPLE bytecode are stored in a library archive, say libfoo. a , it is possible to extract and use them in an LTO link if you are using a linker with plugin support. To create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib ; to show the symbols of object files with GIMPLE bytecode, use gcc-nm.
Those commands require that ar , ranlib and nm have been compiled with plugin support. At link time, use the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process:. With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo. a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized. a are extracted and linked as usual, but they do not participate in the LTO optimization process.
In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with -flto -ffat-lto-objects. Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities.
Use of -fwhole-program is not needed when linker plugin is active see -fuse-linker-plugin. The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts.
The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC. Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF.
If you specify the optional n , the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. This is useful when the Makefile calling GCC is already executing in parallel.
This option likely only works if MAKE is GNU make. Specify the partitioning algorithm used by the link-time optimizer. This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode -flto.
GCC currently supports two LTO compression algorithms. For zstd, valid values are 0 no compression to 19 maximum compression , while zlib supports values from 0 to 9. Values outside this range are clamped to either minimum or maximum of the supported values. If the option is not given, a default balanced compression setting is used. Enables the use of a linker plugin during link-time optimization.
This option relies on plugin support in the linker, which is available in gold or in GNU ld 2. This option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally by non-LTO object or during dynamic linking. Resulting code quality improvements on binaries and shared libraries that use hidden visibility are similar to -fwhole-program.
See -flto for a description of the effect of this flag and how to use it. This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins GNU ld 2. Fat LTO objects are object files that contain both the intermediate language and the object code.
This makes them usable for both LTO linking and normal linking. This option is effective only when compiling with -flto and is ignored at link time. It requires a linker with linker plugin support for basic functionality. Additionally, nm , ar and ranlib need to support linker plugins to allow a full-featured build environment capable of building static libraries etc. GCC provides the gcc-ar , gcc-nm , gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them.
Note that modern binutils provide plugin auto-load mechanism. After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation.
This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates.
When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected. With -fprofile-use all portions of programs not executed during train run are optimized agressively for size rather than speed. In some cases it is not practical to train all possible hot paths in the program.
For example, program may contain functions specific for a given hardware and trianing may not cover all hardware configurations program is run on. With -fprofile-partial-training profile feedback will be ignored for all functions not executed during the train run leading them to be optimized as if they were compiled without profile feedback. This leads to better performance when train run is not representative but also leads to significantly bigger code. Enable profile feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:.
Before you can use this option, you must first generate profiling information. See Instrumentation Options , for information about the -fprofile-generate option. By default, GCC emits an error message if the feedback profiles do not match the source code. Note this may result in poorly optimized code. Additionally, by default, GCC also emits a warning message if the feedback profiles do not exist see -Wmissing-profile.
If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir. Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:.
path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata. afdo in the current directory. You must also supply the unstripped binary for your program to this tool. The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled. Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory.
This option prevents undesirable excess precision on machines such as the where the floating registers of the keep more precision than a double is supposed to have.
Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables. This option allows further control over excess precision on machines where floating-point operations occur in a format with more precision or range than the IEEE standard and interchange floating-point types.
It may, however, yield faster code for programs that do not require the guarantees of these specifications. Do not set errno after calling math functions that are executed with a single instruction, e. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility.
On Darwin systems, the math library never sets errno. There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default. Allow optimizations for floating-point arithmetic that a assume that arguments and results are valid and b may violate IEEE or ANSI standards. When used at link time, it may include libraries or startup files that change the default FPU control word or other similar optimizations.
Enables -fno-signed-zeros , -fno-trapping-math , -fassociative-math and -freciprocal-math. Allow re-association of operands in series of floating-point operations. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect.
For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect. Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. Note that this loses precision and increases the number of flops operating on the value.
Allow optimizations for floating-point arithmetic that ignore the signedness of zero. Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation.
This option requires that -fno-signaling-nans be in effect. Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations.
This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time which may be affected by rounding mode and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes.
This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode. Compile code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point operations.
Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs.
This option implies -ftrapping-math. This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. The default is -ffp-int-builtin-inexact , allowing the exception to be raised, unless C2X or a later C standard is selected.
This option does nothing unless -ftrapping-math is in effect. Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants. When enabled, this option states that a range reduction step is not needed when performing complex division. The default is -fno-cx-limited-range , but is enabled by -ffast-math. Nevertheless, the option applies to all languages.
Complex multiplication and division follow Fortran rules. The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code. After running a program compiled with -fprofile-arcs see Instrumentation Options , you can compile it a second time using -fbranch-probabilities , to improve optimizations based on the number of times each branch was taken.
When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename. gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations.
See details about the file naming in -fprofile-arcs. These can be used to improve optimization. Currently, they are only used in one place: in reorg. If combined with -fprofile-arcs , it adds code so that some data about values of expressions in the program is gathered. With -fbranch-probabilities , it reads back the data gathered from profiling values of expressions for usage in optimizations.
Enabled by -fprofile-generate , -fprofile-use , and -fauto-profile. Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. If combined with -fprofile-arcs , this option instructs the compiler to add code to gather information about values of expressions.
With -fbranch-probabilities , it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator. Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow.
Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job.
Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. It also turns on complete loop peeling i. complete removal of loops with a small constant number of iterations. This option makes code larger, and may or may not make it run faster. Unroll all loops, even if their number of iterations is uncertain when the loop is entered.
This usually makes programs run more slowly. Peels loops for which there is enough information that they do not roll much from profile feedback or static analysis. complete removal of loops with small constant number of iterations. Enables the loop invariant motion pass in the RTL loop optimizer.
Enabled at level -O1 and higher, except for -Og. Enables the loop store motion pass in the GIMPLE loop optimizer. This moves invariant stores to after the end of the loop in exchange for carrying the stored value in a register across the iteration.
Note for this option to have an effect -ftree-loop-im has to be enabled as well. Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches modified according to result of the condition. If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. This is particularly useful for assumed-shape arrays in Fortran where for example it allows better vectorization assuming contiguous accesses.
Place each function or data item into its own section in the output file if the target supports arbitrary sections. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space.
Most systems using the ELF object format have linkers with such optimizations. On AIX, the linker rearranges sections CSECTs based on the call graph. The performance impact varies. Together with a linker garbage collection linker --gc-sections option these options may lead to smaller statically-linked executables after stripping.
Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. These options affect code generation.
They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time. An example of such an optimization is relaxing calls to short call instructions.
This transformation can help to reduce the number of GOT entries and GOT accesses on some targets. usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors , it accesses the variables from a common anchor point instead.
Zero call-used registers at function return to increase program security by either mitigating Return-Oriented Programming ROP attacks or preventing information leakage through registers. In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of instructions.
You can control some of these constants on the command line using the --param option. The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases.
In each case, the value is an integer. The following choices of name are recognized for all targets:. When branch is predicted to be taken with probability lower than this threshold in percent , then it is considered well predictable.
RTL if-conversion tries to remove conditional branches around a block and replace them with conditionally executed instructions. This parameter gives the maximum number of instructions in a block which should be considered for if-conversion.
The compiler will also use other heuristics to decide whether if-conversion is likely to be profitable. RTL if-conversion will try to remove conditional branches around a block and replace them with conditionally executed instructions. These parameters give the maximum permissible cost for the sequence that would be generated by if-conversion depending on whether the branch is statically determined to be predictable or not.
The maximum number of incoming edges to consider for cross-jumping. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.
The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched. The maximum code size expansion factor when copying basic blocks instead of jumping.
The expansion is relative to a jump instruction. The maximum number of instructions to duplicate to a block that jumps to a computed goto. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored.
The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching.
Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time. When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph.
The approximate maximum amount of memory in kB that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done. If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream.
The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources. The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. Maximal loop depth of a call considered by inline heuristics that tries to inline all functions called once.
Several parameters control the tree inliner used in GCC. When you use -finline-functions included in -O3 , a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a different more restrictive limit compared to functions declared inline can be applied --param max-inline-insns-auto. This is bound applied to calls which are considered relevant with -finline-small-functions.
This is bound applied to calls which are optimized for size. Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining.
Number of instructions accounted by inliner for function overhead such as function prologue and epilogue. Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue.
The scale in percents applied to inline-insns-single , inline-insns-single-O2 , inline-insns-auto when inline heuristics hints that inlining is very profitable will enable later optimizations. Same as --param uninlined-function-insns and --param uninlined-function-time but applied to function thunks.
The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth. This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end. Specifies maximal growth of large function caused by inlining in percents.
For example, parameter value limits large function growth to 2. The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth. For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times.
For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth. Specifies maximal overall growth of the compilation unit caused by inlining. For example, parameter value 20 limits unit growth to 1. Cold functions either marked cold via an attribute or by profile feedback are not accounted into the unit size.
Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. For example, parameter value 10 limits unit growth to 1. The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much.
Specifies maximal growth of large stack frames caused by inlining in percents. For example, parameter value limits large stack frame growth to 11 times the original size. Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining.
For functions not declared inline, recursive inlining happens only when -finline-functions included in -O3 is enabled; --param max-inline-insns-recursive-auto applies instead.
For functions not declared inline, recursive inlining happens only when -finline-functions included in -O3 is enabled; --param max-inline-recursive-depth-auto applies instead. Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers.
When profile feedback is available see -fprofile-generate the actual recursion depth can be guessed from the probability that function recurses via a given call expression.
This parameter limits inlining only to call expressions whose probability exceeds the given threshold in percents. Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. Limit of iterations of the early inliner.
This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining. This parameter ought to be bigger than --param modref-max-bases and --param modref-max-refs. Specifies the maximum depth of DFS walk used by modref escape analysis. Setting to 0 disables the analysis completely. A parameter to control whether to use function internal id in profile database lookup.
If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc. The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization.
Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.
A portable media player PMP also including the related digital audio player DAP is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. In contrast, analogue portable audio players play music from non-digital media that use analogue media , such as cassette tapes or vinyl records. Digital audio players DAP were often marketed as MP3 players even if they also supported other file formats and media types.
Generally speaking, they are portable, employing internal or replaceable batteries , equipped with a 3. Some players also include radio tuners , voice recording and other features. DAPs started in the late s following the creation of the MP3 codec in Germany. MP3-playing devices were mostly pioneered by South Korean startups, who by would control the majority of global sales.
The immediate predecessor in the market place of the digital audio player was the portable CD player and prior to that, the personal stereo. In particular, Sony 's Walkman and Discman are the ancestors of digital audio players such as Apple 's iPod.
British scientist Kane Kramer invented the first digital audio player,  which he called the IXI. His UK patent application was not filed until and was issued in in the UK and in the US. hired Kramer as a consultant and presented his work as an example of prior art in the field of digital audio players during their litigation with Burst.
com almost two decades later. Plans were made for a minute stereo memory card and the system was at one time fitted with a hard drive which would have enabled over an hour of recorded digital music. Later Kramer set up a company to promote the IXI and five working prototypes were produced with bit sampling at The Listen Up Player was released in by Audio Highway, an American company led by Nathan Schulhof.
It could store up to an hour of music, but despite getting an award at CES only 25 copies were made. The first production-volume portable digital audio player was The Audible Player also known as MobilePlayer, or Digital Words To Go from Audible.
It only supported playback of digital audio in Audible's proprietary, low-bitrate format which was developed for spoken word recordings. Capacity was limited to 4 MB of internal flash memory, or about 2 hours of play, using a custom rechargeable battery pack. The unit had no display and rudimentary controls. MP3 was introduced as an audio coding standard in It was based on several audio data compression techniques, including the modified discrete cosine transform MDCT , FFT and psychoacoustic methods.
The first car audio hard drive-based MP3 player was also released in by MP32Go and was called the MP32Go Player. It consisted of a 3 GB IBM 2. MP3 became a popular standard format and as a result most digital audio players after this supported it and hence were often called " MP3 players ".
Noticeably, major technology companies did not catch on with the new technology, and instead young startups would come to dominate the early era of MP3 players. The Rio PMP from Diamond Multimedia was introduced in September , a few months after the MPMan, and also featured a 32 MB storage capacity. It was a success during the holiday season, with sales exceeding expectations. Universal City Studios and MP3 players were ruled legal devices.
Eiger Labs and Diamond went on to establish a new segment in the portable audio player market and the following year saw several new manufacturers enter this market. The player would be the start of the Rio line of players. Other early MP3 portables include Sensory Science's Rave MP, the I-Jam IJ, the Creative Labs Nomad and the RCA Lyra. They also used slower parallel port connections to transfer files from PC to player, necessary as most PCs then used the Windows 95 and NT operating systems, which did not have native support for USB connections.
As more users migrated to Windows 98 by , most players transitioned to USB. In the first hard drive based DAP using a 2. Also at the end of the first in-dash MP3 player appeared. The Empeg Car and Rio Car renamed after it was acquired by SONICblue and added to its Rio line of MP3 products offered players in several capacities ranging from 5 to 28 GB.
The unit didn't catch on as SONICblue had hoped, though, and was discontinued in the fall of For the next couple of years, there were particularly much output from South Korean companies, namely the startups iRiver brand of Reigncom , Mpio brand of DigitalWay and Cowon. Sony entered the digital audio player market in with the Vaio Music Clip and Memory Stick Walkman , however they were technically not MP3 players as it did not support the MP3 format but instead Sony's own ATRAC format and WMA.
The company's first MP3-supporting Walkman player did not come until This DAP plays audio files using ATRAC compression stored on a removable Memory Stick. Designed by Samsung Electronics , the Samsung YEPP line were first released in with the aim of making the smallest music players on the market.
The name borrowed the jukebox metaphor popularised by Remote Solution , also used by Archos. Later players in the Creative NOMAD range used microdrives rather than laptop drives. In October , South Korean software company Cowon Systems released their first MP3 player, the CW, under the brand name iAUDIO. Since then the company has released many different players. In December , some months after the Creative's NOMAD Jukebox , Archos released its Jukebox with a 6GB hard drive.
Philips also released a player called the Rush. While popularly being called MP3 players at the time, most players could play more than just the MP3 file format, for example Windows Media Audio WMA , Advanced Audio Coding AAC , Vorbis , FLAC , Speex and Ogg.
Many MP3 players can encode directly to MP3 or other digital audio format directly from a line in audio signal radio, voice, etc. Devices such as CD players can be connected to the MP3 player using the USB port in order to directly play music from the memory of the player without the use of a computer. They can be independently obtained and upgradable one can change the head or the body; i.
to add more memory. On 23 October , Apple Computer unveiled the first generation iPod , a 5 GB hard drive based DAP with a 1. With the development of a spartan user interface and a smaller form factor, the iPod was initially popular within the Macintosh community. In July , Apple introduced the second generation update to the iPod, which was compatible with Windows computers through Musicmatch Jukebox.
iPods quickly became the most popular DAP product and led the fast growth of this market during the early and mid s. In , Archos released the first "portable media player" PMP , the Archos Jukebox Multimedia  with a little 1.
Manufacturers have since implemented abilities to view images and play videos into their devices. The next year, Archos released another multimedia jukebox , the AV , with a 3. In the same year, Toshiba released the first Gigabeat. In , Dell launched a line of portable digital music players called Dell DJ. They were discontinued by The name "MP4 player" was a marketing term for inexpensive portable media players, usually from little known or generic device manufacturers.
mp4 container format. Instead, the term refers to their ability to play more file types than just MP3. In this sense, in some markets like Brazil, any new function added to a given media player is followed by an increase in the number, for example an MP5 or MP12 Player,  despite there being no corresponding MPEG-5 standard as of [update] , the current standard, still being developed, is MPEG iriver of South Korea originally made portable CD players and then started making digital audio players and portable media players from Creative also introduced the ZEN line.
Both of these attained high popularity in some regions. In , Microsoft attempted to take advantage of the growing PMP market by launching the Portable Media Center PMC platform.
It was introduced at the Consumer Electronics Show with the announcement of the Zen Portable Media Center ,  which was co-developed by Creative. The Microsoft Zune series would later be based on the Gigabeat S , one of the PMC-implemented players. In May , flash memory maker SanDisk entered the PMP market with the Sansa line of players, starting with the e series, and then following up with the m series, and c series.
In , Apple introduced the iPod Touch , the first iPod with a multi-touch screen. Some similar products existed before such as the iriver clix in In South Korea, sales of MP3 players peaked in , but started declining afterwards. This was driven partly by the launch of mobile television services DMB , which along with increased demand of movies on the go led to a transition away from music-only players to PMPs.
European buying patterns differed; while Apple was in a particularly strong position in the United Kingdom, continental Western Europe generally preferred cheaper, often Chinese rebranded players under local brands such as Grundig. Creative was the top selling maker in its home country of Singapore. In China, local brands Newman, DEC and Aigo were noted as the top vendors as of Samsung SPH-M , the first mobile phone with built-in MP3 player was produced in South Korea in August The innovation spread rapidly across the globe and by , more than half of all music sold in South Korea was sold directly to mobile phones and all major handset makers in the world had released MP3 playing phones.
By , more MP3 playing mobile phones were sold than all stand-alone MP3 players put together. The rapid rise of the media player in phones was quoted by Apple as a primary reason for developing the iPhone. In , the number of phones that could play media was over 1 billion. Mobile phones with PMP functionalities such as video playback also started appearing in the s.
Other non-phone products such as the PlayStation Portable and PlayStation Vita have also been considered to be PMPs. DAPs and PMPs have declined in popularity after the late s due to increasing worldwide adoption of smartphones that already come with PMP functionalities. In the EU , demand for MP3 players peaked in with Both sales and revenue experienced a double-digit shrinkage for the first time in Meanwhile, sales of the best selling product, the iPod, was eclipsed by the company's iPhone smartphone by DAPs continue to be made in lower volumes by manufacturers such as SanDisk, Sony, IRIVER, Philips, Apple, Cowon, and a range of Chinese manufacturers namely Aigo, Newsmy, PYLE and ONDA.
Usually, a colour liquid crystal display LCD or organic light-emitting diode OLED screen is used as a display for PMPs that have a screen.
Various players include the ability to record video, usually with the aid of optional accessories or cables, and audio, with a built-in microphone or from a line out cable or FM tuner. Some players include readers for memory cards , which are advertised to equip players with extra storage or transferring media.
In some players, features of a personal organiser are emulated, or support for video games , like the iriver clix through compatibility of Adobe Flash Lite or the PlayStation Portable , is included.
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o into functions in foo. Many such devices also tend to be smartphones. Navigate to the downloaded DEM Config file and make any changes necessary. But Diamond won a legal victory on the shoulders of the Sony Corp. Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. This leads to better performance when train run is not representative but also leads to significantly bigger code.Use of -fwhole-program is not needed when linker plugin is active see -fuse-linker-plugin, binary option sinha a. In this example, all of B is overwritten by A, and the result contains policies from baselines A and C. The parent-level admin has binary option sinha a and can edit, delete, and assign all baselines at the parent and children levels. Click Add Version to add a new version of the DEM Config. When applied, the baseline at the top of the stack has the greatest precedence and will override any overlapping policies. Tuning this may improve compilation speed; it has no effect on code generation. Perform forward propagation on trees.