forked from OSchip/llvm-project
3a8ea8609b
As discussed on llvm-dev: http://lists.llvm.org/pipermail/llvm-dev/2020-April/140729.html This is hopefully the final remaining showstopper before we can remove the 'experimental' from the reduction intrinsics. No behavior was specified for the FP min/max reductions, so we have a mess of different interpretations. There are a few potential options for the semantics of these max/min ops. I think this is the simplest based on current behavior/implementation: make the reductions inherit from the existing llvm.maxnum/minnum intrinsics. These correspond to libm fmax/fmin, and those are similar to the (now deprecated?) IEEE-754 maxNum/minNum functions (NaNs are treated as missing data). So the default expansion creates calls to libm functions. Another option would be to inherit from llvm.maximum/minimum (NaNs propagate), but most targets just crash in codegen when given those nodes because no default expansion was ever implemented AFAICT. We could also just assume 'nnan' semantics by default (we are already assuming 'nsz' semantics in the maxnum/minnum intrinsics), but some targets (AArch64, PowerPC) support the more defined behavior, so it doesn't make much sense to not allow a tighter spec. Fast-math-flags (nnan) can be used to loosen the semantics. (Note that D67507 was proposed to update the LangRef to acknowledge the more recent IEEE-754 2019 standard, but that patch seems to have stalled. If we do update based on the new standard, the reduction instructions can seamlessly inherit from whatever updates are made to the max/min intrinsics.) x86 sees a regression here on 'nnan' tests because we have underlying, longstanding bugs in FMF creation/propagation. Those need to be fixed apart from this change (for example: https://llvm.org/PR35538). The expansion sequence before this patch may not have been correct. Differential Revision: https://reviews.llvm.org/D87391 |
||
|---|---|---|
| .. | ||
| AMDGPU | ||
| CommandGuide | ||
| DependenceGraphs | ||
| Frontend | ||
| GlobalISel | ||
| HistoricalNotes | ||
| PDB | ||
| Proposals | ||
| TableGen | ||
| _ocamldoc | ||
| _static | ||
| _templates | ||
| _themes/llvm-theme | ||
| tutorial | ||
| AMDGPUDwarfExtensionsForHeterogeneousDebugging.rst | ||
| AMDGPUInstructionNotation.rst | ||
| AMDGPUInstructionSyntax.rst | ||
| AMDGPUModifierSyntax.rst | ||
| AMDGPUOperandSyntax.rst | ||
| AMDGPUUsage.rst | ||
| ARM-BE-bitcastfail.png | ||
| ARM-BE-bitcastsuccess.png | ||
| ARM-BE-ld1.png | ||
| ARM-BE-ldr.png | ||
| AddingConstrainedIntrinsics.rst | ||
| AdvancedBuilds.rst | ||
| AliasAnalysis.rst | ||
| Atomics.rst | ||
| Benchmarking.rst | ||
| BigEndianNEON.rst | ||
| BitCodeFormat.rst | ||
| BlockFrequencyTerminology.rst | ||
| BranchWeightMetadata.rst | ||
| BugLifeCycle.rst | ||
| Bugpoint.rst | ||
| BugpointRedesign.md | ||
| BuildingADistribution.rst | ||
| CFIVerify.rst | ||
| CMake.rst | ||
| CMakeLists.txt | ||
| CMakePrimer.rst | ||
| CodeGenerator.rst | ||
| CodeOfConduct.rst | ||
| CodeReview.rst | ||
| CodingStandards.rst | ||
| CommandLine.rst | ||
| CompileCudaWithLLVM.rst | ||
| CompilerWriterInfo.rst | ||
| Contributing.rst | ||
| Coroutines.rst | ||
| CoverageMappingFormat.rst | ||
| DebuggingJITedCode.rst | ||
| DeveloperPolicy.rst | ||
| Docker.rst | ||
| ExceptionHandling.rst | ||
| ExtendedIntegerResults.txt | ||
| ExtendingLLVM.rst | ||
| Extensions.rst | ||
| FAQ.rst | ||
| FaultMaps.rst | ||
| FuzzingLLVM.rst | ||
| GarbageCollection.rst | ||
| GetElementPtr.rst | ||
| GettingInvolved.rst | ||
| GettingStarted.rst | ||
| GettingStartedTutorials.rst | ||
| GettingStartedVS.rst | ||
| GitBisecting.rst | ||
| GoldPlugin.rst | ||
| GwpAsan.rst | ||
| HowToAddABuilder.rst | ||
| HowToBuildOnARM.rst | ||
| HowToBuildWithPGO.rst | ||
| HowToCrossCompileBuiltinsOnArm.rst | ||
| HowToCrossCompileLLVM.rst | ||
| HowToReleaseLLVM.rst | ||
| HowToSetUpLLVMStyleRTTI.rst | ||
| HowToSubmitABug.rst | ||
| HowToUpdateDebugInfo.rst | ||
| HowToUseAttributes.rst | ||
| HowToUseInstrMappings.rst | ||
| InAlloca.rst | ||
| LLVMBuild.rst | ||
| LLVMBuild.txt | ||
| LangRef.rst | ||
| Lexicon.rst | ||
| LibFuzzer.rst | ||
| LinkTimeOptimization.rst | ||
| LoopTerminology.rst | ||
| MCJIT-creation.png | ||
| MCJIT-dyld-load.png | ||
| MCJIT-engine-builder.png | ||
| MCJIT-load-object.png | ||
| MCJIT-load.png | ||
| MCJIT-resolve-relocations.png | ||
| MCJITDesignAndImplementation.rst | ||
| MIRLangRef.rst | ||
| Makefile.sphinx | ||
| MarkdownQuickstartTemplate.md | ||
| MarkedUpDisassembly.rst | ||
| MeetupGuidelines.rst | ||
| MemTagSanitizer.rst | ||
| MemorySSA.rst | ||
| MergeFunctions.rst | ||
| NVPTXUsage.rst | ||
| ORCv2.rst | ||
| OptBisect.rst | ||
| Packaging.rst | ||
| Passes.rst | ||
| Phabricator.rst | ||
| ProgrammersManual.rst | ||
| Projects.rst | ||
| README.txt | ||
| Reference.rst | ||
| ReleaseNotes.rst | ||
| ReleaseProcess.rst | ||
| Remarks.rst | ||
| ReportingGuide.rst | ||
| ScudoHardenedAllocator.rst | ||
| Security.rst | ||
| SegmentedStacks.rst | ||
| SourceLevelDebugging.rst | ||
| SpeculativeLoadHardening.md | ||
| SphinxQuickstartTemplate.rst | ||
| StackMaps.rst | ||
| StackSafetyAnalysis.rst | ||
| Statepoints.rst | ||
| SupportLibrary.rst | ||
| SystemLibrary.rst | ||
| TableGenFundamentals.rst | ||
| TestSuiteGuide.md | ||
| TestSuiteMakefileGuide.rst | ||
| TestingGuide.rst | ||
| TransformMetadata.rst | ||
| TypeMetadata.rst | ||
| UserGuides.rst | ||
| Vectorizers.rst | ||
| WritingAnLLVMBackend.rst | ||
| WritingAnLLVMPass.rst | ||
| XRay.rst | ||
| XRayExample.rst | ||
| XRayFDRFormat.rst | ||
| YamlIO.rst | ||
| conf.py | ||
| doxygen-mainpage.dox | ||
| doxygen.cfg.in | ||
| gcc-loops.png | ||
| index.rst | ||
| linpack-pc.png | ||
| llvm-objdump.1 | ||
| loop-terminology-guarded-loop.png | ||
| loop-terminology-initial-loop.png | ||
| loop-terminology-rotated-loop.png | ||
| make.bat | ||
| re_format.7 | ||
| speculative_load_hardening_microbenchmarks.png | ||
| yaml2obj.rst | ||
README.txt
LLVM Documentation
==================
LLVM's documentation is written in reStructuredText, a lightweight
plaintext markup language (file extension `.rst`). While the
reStructuredText documentation should be quite readable in source form, it
is mostly meant to be processed by the Sphinx documentation generation
system to create HTML pages which are hosted on <https://llvm.org/docs/> and
updated after every commit. Manpage output is also supported, see below.
If you instead would like to generate and view the HTML locally, install
Sphinx <http://sphinx-doc.org/> and then do:
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_HTML=true <src-dir>
make -j3 docs-llvm-html
$BROWSER <build-dir>/docs//html/index.html
The mapping between reStructuredText files and generated documentation is
`docs/Foo.rst` <-> `<build-dir>/docs//html/Foo.html` <-> `https://llvm.org/docs/Foo.html`.
If you are interested in writing new documentation, you will want to read
`SphinxQuickstartTemplate.rst` which will get you writing documentation
very fast and includes examples of the most important reStructuredText
markup syntax.
Manpage Output
===============
Building the manpages is similar to building the HTML documentation. The
primary difference is to use the `man` makefile target, instead of the
default (which is `html`). Sphinx then produces the man pages in the
directory `<build-dir>/docs/man/`.
cd <build-dir>
cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_MAN=true <src-dir>
make -j3 docs-llvm-man
man -l >build-dir>/docs/man/FileCheck.1
The correspondence between .rst files and man pages is
`docs/CommandGuide/Foo.rst` <-> `<build-dir>/docs//man/Foo.1`.
These .rst files are also included during HTML generation so they are also
viewable online (as noted above) at e.g.
`https://llvm.org/docs/CommandGuide/Foo.html`.
Checking links
==============
The reachability of external links in the documentation can be checked by
running:
cd docs/
make -f Makefile.sphinx linkcheck
Doxygen page Output
==============
Install doxygen <http://www.stack.nl/~dimitri/doxygen/download.html> and dot2tex <https://dot2tex.readthedocs.io/en/latest>.
cd <build-dir>
cmake -DLLVM_ENABLE_DOXYGEN=On <llvm-top-src-dir>
make doxygen-llvm # for LLVM docs
make doxygen-clang # for clang docs
It will generate html in
<build-dir>/docs/doxygen/html # for LLVM docs
<build-dir>/tools/clang/docs/doxygen/html # for clang docs