forked from OSchip/llvm-project
b9e65cbddf
This patch introduces a new instinsic `@llvm.experimental.widenable_condition` that allows explicit representation for guards. It is an alternative to using `@llvm.experimental.guard` intrinsic that does not contain implicit control flow. We keep finding places where `@llvm.experimental.guard` is not supported or treated too conservatively, and there are 2 reasons to that: - `@llvm.experimental.guard` has memory write side effect to model implicit control flow, and this sometimes confuses passes and analyzes that work with memory; - Not all passes and analysis are aware of the semantics of guards. These passes treat them as regular throwing call and have no idea that the condition of guard may be used to prove something. One well-known place which had caused us troubles in the past is explicit loop iteration count calculation in SCEV. Another example is new loop unswitching which is not aware of guards. Whenever a new pass appears, we potentially have this problem there. Rather than go and fix all these places (and commit to keep track of them and add support in future), it seems more reasonable to leverage the existing optimizer's logic as much as possible. The only significant difference between guards and regular explicit branches is that guard's condition can be widened. It means that a guard contains (explicitly or implicitly) a `deopt` block successor, and it is always legal to go there no matter what the guard condition is. The other successor is a guarded block, and it is only legal to go there if the condition is true. This patch introduces a new explicit form of guards alternative to `@llvm.experimental.guard` intrinsic. Now a widenable guard can be represented in the CFG explicitly like this: %widenable_condition = call i1 @llvm.experimental.widenable.condition() %new_condition = and i1 %cond, %widenable_condition br i1 %new_condition, label %guarded, label %deopt guarded: ; Guarded instructions deopt: call type @llvm.experimental.deoptimize(<args...>) [ "deopt"(<deopt_args...>) ] The new intrinsic `@llvm.experimental.widenable.condition` has semantics of an `undef`, but the intrinsic prevents the optimizer from folding it early. This form should exploit all optimization boons provided to `br` instuction, and it still can be widened by replacing the result of `@llvm.experimental.widenable.condition()` with `and` with any arbitrary boolean value (as long as the branch that is taken when it is `false` has a deopt and has no side-effects). For more motivation, please check llvm-dev discussion "[llvm-dev] Giving up using implicit control flow in guards". This patch introduces this new intrinsic with respective LangRef changes and a pass that converts old-style guards (expressed as intrinsics) into the new form. The naming discussion is still ungoing. Merging this to unblock further items. We can later change the name of this intrinsic. Reviewed By: reames, fedor.sergeev, sanjoy Differential Revision: https://reviews.llvm.org/D51207 llvm-svn: 348593 |
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CommandGuide | ||
Frontend | ||
HistoricalNotes | ||
PDB | ||
Proposals | ||
TableGen | ||
_ocamldoc | ||
_static | ||
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_themes/llvm-theme | ||
tutorial | ||
AMDGPUAsmGFX7.rst | ||
AMDGPUAsmGFX8.rst | ||
AMDGPUAsmGFX9.rst | ||
AMDGPUOperandSyntax.rst | ||
AMDGPUUsage.rst | ||
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AdvancedBuilds.rst | ||
AliasAnalysis.rst | ||
Atomics.rst | ||
Benchmarking.rst | ||
BigEndianNEON.rst | ||
BitCodeFormat.rst | ||
BlockFrequencyTerminology.rst | ||
BranchWeightMetadata.rst | ||
BugLifeCycle.rst | ||
Bugpoint.rst | ||
CFIVerify.rst | ||
CMake.rst | ||
CMakeLists.txt | ||
CMakePrimer.rst | ||
CodeGenerator.rst | ||
CodeOfConduct.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 | ||
GettingStarted.rst | ||
GettingStartedVS.rst | ||
GlobalISel.rst | ||
GoldPlugin.rst | ||
HowToAddABuilder.rst | ||
HowToBuildOnARM.rst | ||
HowToBuildWithPGO.rst | ||
HowToCrossCompileBuiltinsOnArm.rst | ||
HowToCrossCompileLLVM.rst | ||
HowToReleaseLLVM.rst | ||
HowToSetUpLLVMStyleRTTI.rst | ||
HowToSubmitABug.rst | ||
HowToUseAttributes.rst | ||
HowToUseInstrMappings.rst | ||
InAlloca.rst | ||
LLVMBuild.rst | ||
LLVMBuild.txt | ||
LangRef.rst | ||
Lexicon.rst | ||
LibFuzzer.rst | ||
LinkTimeOptimization.rst | ||
MCJIT-creation.png | ||
MCJIT-dyld-load.png | ||
MCJIT-engine-builder.png | ||
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MCJITDesignAndImplementation.rst | ||
MIRLangRef.rst | ||
Makefile.sphinx | ||
MarkdownQuickstartTemplate.md | ||
MarkedUpDisassembly.rst | ||
MemorySSA.rst | ||
MergeFunctions.rst | ||
NVPTXUsage.rst | ||
OptBisect.rst | ||
Packaging.rst | ||
Passes.rst | ||
Phabricator.rst | ||
ProgrammersManual.rst | ||
Projects.rst | ||
README.txt | ||
ReleaseNotes.rst | ||
ReleaseProcess.rst | ||
ReportingGuide.rst | ||
ScudoHardenedAllocator.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 | ||
TypeMetadata.rst | ||
Vectorizers.rst | ||
WritingAnLLVMBackend.rst | ||
WritingAnLLVMPass.rst | ||
XRay.rst | ||
XRayExample.rst | ||
XRayFDRFormat.rst | ||
YamlIO.rst | ||
conf.py | ||
doxygen-mainpage.dox | ||
doxygen.cfg.in | ||
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index.rst | ||
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make.bat | ||
re_format.7 | ||
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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 <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 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