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Recently we improved the lowering of low overhead loops and tail
predicated loops, but concentrated first on the DLS do style loops. This
extends those improvements over to the WLS while loops, improving the
chance of lowering them successfully. To do this the lowering has to
change a little as the instructions are terminators that produce a value
- something that needs to be treated carefully.
Lowering starts at the Hardware Loop pass, inserting a new
llvm.test.start.loop.iterations that produces both an i1 to control the
loop entry and an i32 similar to the llvm.start.loop.iterations
intrinsic added for do loops. This feeds into the loop phi, properly
gluing the values together:
%wls = call { i32, i1 } @llvm.test.start.loop.iterations.i32(i32 %div)
%wls0 = extractvalue { i32, i1 } %wls, 0
%wls1 = extractvalue { i32, i1 } %wls, 1
br i1 %wls1, label %loop.ph, label %loop.exit
...
loop:
%lsr.iv = phi i32 [ %wls0, %loop.ph ], [ %iv.next, %loop ]
..
%iv.next = call i32 @llvm.loop.decrement.reg.i32(i32 %lsr.iv, i32 1)
%cmp = icmp ne i32 %iv.next, 0
br i1 %cmp, label %loop, label %loop.exit
The llvm.test.start.loop.iterations need to be lowered through ISel
lowering as a pair of WLS and WLSSETUP nodes, which each get converted
to t2WhileLoopSetup and t2WhileLoopStart Pseudos. This helps prevent
t2WhileLoopStart from being a terminator that produces a value,
something difficult to control at that stage in the pipeline. Instead
the t2WhileLoopSetup produces the value of LR (essentially acting as a
lr = subs rn, 0), t2WhileLoopStart consumes that lr value (the Bcc).
These are then converted into a single t2WhileLoopStartLR at the same
point as t2DoLoopStartTP and t2LoopEndDec. Otherwise we revert the loop
to prevent them from progressing further in the pipeline. The
t2WhileLoopStartLR is a single instruction that takes a GPR and produces
LR, similar to the WLS instruction.
%1:gprlr = t2WhileLoopStartLR %0:rgpr, %bb.3
t2B %bb.1
...
bb.2.loop:
%2:gprlr = PHI %1:gprlr, %bb.1, %3:gprlr, %bb.2
...
%3:gprlr = t2LoopEndDec %2:gprlr, %bb.2
t2B %bb.3
The t2WhileLoopStartLR can then be treated similar to the other low
overhead loop pseudos, eventually being lowered to a WLS providing the
branches are within range.
Differential Revision: https://reviews.llvm.org/D97729
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| .. | ||
| _ocamldoc | ||
| _static | ||
| _templates | ||
| _themes/llvm-theme | ||
| AMDGPU | ||
| CommandGuide | ||
| DependenceGraphs | ||
| Frontend | ||
| GlobalISel | ||
| HistoricalNotes | ||
| PDB | ||
| Proposals | ||
| TableGen | ||
| tutorial | ||
| AddingConstrainedIntrinsics.rst | ||
| AdvancedBuilds.rst | ||
| AliasAnalysis.rst | ||
| 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 | ||
| 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 | ||
| conf.py | ||
| Contributing.rst | ||
| Coroutines.rst | ||
| CoverageMappingFormat.rst | ||
| DebuggingJITedCode.rst | ||
| DeveloperPolicy.rst | ||
| Docker.rst | ||
| doxygen-mainpage.dox | ||
| doxygen.cfg.in | ||
| epilogue-vectorization-cfg.png | ||
| ExceptionHandling.rst | ||
| ExtendedIntegerResults.txt | ||
| ExtendingLLVM.rst | ||
| Extensions.rst | ||
| FAQ.rst | ||
| FaultMaps.rst | ||
| FuzzingLLVM.rst | ||
| GarbageCollection.rst | ||
| gcc-loops.png | ||
| GetElementPtr.rst | ||
| GettingInvolved.rst | ||
| GettingStarted.rst | ||
| GettingStartedTutorials.rst | ||
| GettingStartedVS.rst | ||
| GitBisecting.rst | ||
| GoldPlugin.rst | ||
| GwpAsan.rst | ||
| HowToAddABuilder.rst | ||
| HowToBuildOnARM.rst | ||
| HowToBuildWindowsItaniumPrograms.rst | ||
| HowToBuildWithPGO.rst | ||
| HowToCrossCompileBuiltinsOnArm.rst | ||
| HowToCrossCompileLLVM.rst | ||
| HowToReleaseLLVM.rst | ||
| HowToSetUpLLVMStyleRTTI.rst | ||
| HowToSubmitABug.rst | ||
| HowToUpdateDebugInfo.rst | ||
| HowToUseAttributes.rst | ||
| HowToUseInstrMappings.rst | ||
| InAlloca.rst | ||
| index.rst | ||
| JITLink.rst | ||
| LangRef.rst | ||
| Lexicon.rst | ||
| LibFuzzer.rst | ||
| LinkTimeOptimization.rst | ||
| linpack-pc.png | ||
| llvm-objdump.1 | ||
| loop-guard.svg | ||
| loop-irreducible.svg | ||
| loop-merge.svg | ||
| loop-nested.svg | ||
| loop-nonmaximal.svg | ||
| loop-separate.svg | ||
| loop-single.svg | ||
| loop-terminology-guarded-loop.png | ||
| loop-terminology-initial-loop.png | ||
| loop-terminology-rotated-loop.png | ||
| loop-terminology.svg | ||
| LoopTerminology.rst | ||
| make.bat | ||
| Makefile.sphinx | ||
| MarkdownQuickstartTemplate.md | ||
| MarkedUpDisassembly.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 | ||
| MeetupGuidelines.rst | ||
| MemorySSA.rst | ||
| MemTagSanitizer.rst | ||
| MergeFunctions.rst | ||
| MIRLangRef.rst | ||
| NewPassManager.rst | ||
| NVPTXUsage.rst | ||
| OptBisect.rst | ||
| ORCv2.rst | ||
| Packaging.rst | ||
| Passes.rst | ||
| Phabricator.rst | ||
| ProgrammersManual.rst | ||
| Projects.rst | ||
| re_format.7 | ||
| README.txt | ||
| Reference.rst | ||
| ReleaseNotes.rst | ||
| ReleaseProcess.rst | ||
| Remarks.rst | ||
| ReportingGuide.rst | ||
| ScudoHardenedAllocator.rst | ||
| Security.rst | ||
| SegmentedStacks.rst | ||
| SourceLevelDebugging.rst | ||
| speculative_load_hardening_microbenchmarks.png | ||
| SpeculativeLoadHardening.md | ||
| SphinxQuickstartTemplate.rst | ||
| StackMaps.rst | ||
| StackSafetyAnalysis.rst | ||
| Statepoints.rst | ||
| SupportLibrary.rst | ||
| SupportPolicy.rst | ||
| SystemLibrary.rst | ||
| TableGenFundamentals.rst | ||
| TestingGuide.rst | ||
| TestSuiteGuide.md | ||
| TestSuiteMakefileGuide.rst | ||
| TransformMetadata.rst | ||
| TypeMetadata.rst | ||
| UserGuides.rst | ||
| Vectorizers.rst | ||
| WritingAnLLVMBackend.rst | ||
| WritingAnLLVMNewPMPass.rst | ||
| WritingAnLLVMPass.rst | ||
| XRay.rst | ||
| XRayExample.rst | ||
| XRayFDRFormat.rst | ||
| yaml2obj.rst | ||
| YamlIO.rst | ||
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