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Since r279760, we've been marking as legal operations on narrow integer types that have wider legal equivalents (for instance, G_ADD s8). Compared to legalizing these operations, this reduced the amount of extends/truncates required, but was always a weird legalization decision made at selection time. So far, we haven't been able to formalize it in a way that permits the selector generated from SelectionDAG patterns to be sufficient. Using a wide instruction (say, s64), when a narrower instruction exists (s32) would introduce register class incompatibilities (when one narrow generic instruction is selected to the wider variant, but another is selected to the narrower variant). It's also impractical to limit which narrow operations are matched for which instruction, as restricting "narrow selection" to ranges of types clashes with potentially incompatible instruction predicates. Concerns were also raised regarding MIPS64's sign-extended register assumptions, as well as wrapping behavior. See discussions in https://reviews.llvm.org/D26878. Instead, legalize the operations. Should we ever revert to selecting these narrow operations, we should try to represent this more accurately: for instance, by separating a "concrete" type on operations, and an "underlying" type on vregs, we could move the "this narrow-looking op is really legal" decision to the legalizer, and let the selector use the "underlying" vreg type only, which would be guaranteed to map to a register class. In any case, we eventually should mitigate: - the performance impact by selecting no-op extract/truncates to COPYs (which we currently do), and the COPYs to register reuses (which we don't do yet). - the compile-time impact by optimizing away extract/truncate sequences in the legalizer. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292827 91177308-0d34-0410-b5e6-96231b3b80d8 |
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_themes/llvm-theme | ||
CommandGuide | ||
Frontend | ||
HistoricalNotes | ||
PDB | ||
Proposals | ||
TableGen | ||
tutorial | ||
AdvancedBuilds.rst | ||
AliasAnalysis.rst | ||
AMDGPUUsage.rst | ||
ARM-BE-bitcastfail.png | ||
ARM-BE-bitcastsuccess.png | ||
ARM-BE-ld1.png | ||
ARM-BE-ldr.png | ||
Atomics.rst | ||
BigEndianNEON.rst | ||
BitCodeFormat.rst | ||
BlockFrequencyTerminology.rst | ||
BranchWeightMetadata.rst | ||
Bugpoint.rst | ||
CMake.rst | ||
CMakeLists.txt | ||
CMakePrimer.rst | ||
CodeGenerator.rst | ||
CodeOfConduct.rst | ||
CodingStandards.rst | ||
CommandLine.rst | ||
CompileCudaWithLLVM.rst | ||
CompilerWriterInfo.rst | ||
conf.py | ||
Coroutines.rst | ||
CoverageMappingFormat.rst | ||
DebuggingJITedCode.rst | ||
DeveloperPolicy.rst | ||
doxygen-mainpage.dox | ||
doxygen.cfg.in | ||
Dummy.html | ||
ExceptionHandling.rst | ||
ExtendedIntegerResults.txt | ||
ExtendingLLVM.rst | ||
Extensions.rst | ||
FAQ.rst | ||
FaultMaps.rst | ||
GarbageCollection.rst | ||
gcc-loops.png | ||
GetElementPtr.rst | ||
GettingStarted.rst | ||
GettingStartedVS.rst | ||
GlobalISel.rst | ||
GoldPlugin.rst | ||
HowToAddABuilder.rst | ||
HowToBuildOnARM.rst | ||
HowToCrossCompileLLVM.rst | ||
HowToReleaseLLVM.rst | ||
HowToSetUpLLVMStyleRTTI.rst | ||
HowToSubmitABug.rst | ||
HowToUseAttributes.rst | ||
HowToUseInstrMappings.rst | ||
InAlloca.rst | ||
index.rst | ||
LangRef.rst | ||
Lexicon.rst | ||
LibFuzzer.rst | ||
LinkTimeOptimization.rst | ||
linpack-pc.png | ||
LLVMBuild.rst | ||
LLVMBuild.txt | ||
make.bat | ||
Makefile.sphinx | ||
MarkedUpDisassembly.rst | ||
MCJIT-creation.png | ||
MCJIT-dyld-load.png | ||
MCJIT-engine-builder.png | ||
MCJIT-load-object.png | ||
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MCJITDesignAndImplementation.rst | ||
MemorySSA.rst | ||
MergeFunctions.rst | ||
MIRLangRef.rst | ||
NVPTXUsage.rst | ||
OptBisect.rst | ||
Packaging.rst | ||
Passes.rst | ||
Phabricator.rst | ||
ProgrammersManual.rst | ||
Projects.rst | ||
re_format.7 | ||
README.txt | ||
ReleaseNotes.rst | ||
ReleaseProcess.rst | ||
ReportingGuide.rst | ||
ScudoHardenedAllocator.rst | ||
SegmentedStacks.rst | ||
SourceLevelDebugging.rst | ||
SphinxQuickstartTemplate.rst | ||
StackMaps.rst | ||
Statepoints.rst | ||
SystemLibrary.rst | ||
TableGenFundamentals.rst | ||
TestingGuide.rst | ||
TestSuiteMakefileGuide.rst | ||
TypeMetadata.rst | ||
Vectorizers.rst | ||
WritingAnLLVMBackend.rst | ||
WritingAnLLVMPass.rst | ||
XRay.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 <http://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` <-> `http://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. `http://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