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Uniformity analysis is a generalization of divergence analysis to
include irreducible control flow:
1. The proposed spec presents a notion of "maximal convergence" that
captures the existing convention of converging threads at the
headers of natual loops.
2. Maximal convergence is then extended to irreducible cycles. The
identity of irreducible cycles is determined by the choices made
in a depth-first traversal of the control flow graph. Uniformity
analysis uses criteria that depend only on closed paths and not
cycles, to determine maximal convergence. This makes it a
conservative analysis that is independent of the effect of DFS on
CycleInfo.
3. The analysis is implemented as a template that can be
instantiated for both LLVM IR and Machine IR.
Validation:
- passes existing tests for divergence analysis
- passes new tests with irreducible control flow
- passes equivalent tests in MIR and GMIR
Based on concepts originally outlined by
Nicolai Haehnle <nicolai.haehnle@amd.com>
With contributions from Ruiling Song <ruiling.song@amd.com> and
Jay Foad <jay.foad@amd.com>.
Support for GMIR and lit tests for GMIR/MIR added by
Yashwant Singh <yashwant.singh@amd.com>.
Differential Revision: https://reviews.llvm.org/D130746
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Reference
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=========
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LLVM and API reference documentation.
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.. contents::
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:local:
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.. toctree::
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:hidden:
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Atomics
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BitCodeFormat
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BlockFrequencyTerminology
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BranchWeightMetadata
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Bugpoint
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CommandGuide/index
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ConvergenceAndUniformity
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Coroutines
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DependenceGraphs/index
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ExceptionHandling
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Extensions
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FaultMaps
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FuzzingLLVM
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GarbageCollection
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GetElementPtr
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GlobalISel/index
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GwpAsan
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HowToSetUpLLVMStyleRTTI
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HowToUseAttributes
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InAlloca
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LangRef
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LibFuzzer
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MarkedUpDisassembly
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MIRLangRef
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OptBisect
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PCSectionsMetadata
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PDB/index
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PointerAuth
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ScudoHardenedAllocator
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MemTagSanitizer
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Security
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SecurityTransparencyReports
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SegmentedStacks
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StackMaps
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SpeculativeLoadHardening
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Statepoints
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SymbolizerMarkupFormat
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SystemLibrary
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TestingGuide
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TransformMetadata
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TypeMetadata
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XRay
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XRayExample
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XRayFDRFormat
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YamlIO
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API Reference
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-------------
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`Doxygen generated documentation <https://llvm.org/doxygen/>`_
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(`classes <https://llvm.org/doxygen/inherits.html>`_)
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:doc:`HowToUseAttributes`
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Answers some questions about the new Attributes infrastructure.
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LLVM Reference
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--------------
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======================
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Command Line Utilities
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======================
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:doc:`LLVM Command Guide <CommandGuide/index>`
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A reference manual for the LLVM command line utilities ("man" pages for LLVM
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tools).
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:doc:`Bugpoint`
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Automatic bug finder and test-case reducer description and usage
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information.
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:doc:`OptBisect`
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A command line option for debugging optimization-induced failures.
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:doc:`SymbolizerMarkupFormat`
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A reference for the log symbolizer markup accepted by ``llvm-symbolizer``.
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:doc:`The Microsoft PDB File Format <PDB/index>`
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A detailed description of the Microsoft PDB (Program Database) file format.
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==================
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Garbage Collection
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==================
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:doc:`GarbageCollection`
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The interfaces source-language compilers should use for compiling GC'd
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programs.
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:doc:`Statepoints`
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This describes a set of experimental extensions for garbage
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collection support.
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=========
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LibFuzzer
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=========
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:doc:`LibFuzzer`
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A library for writing in-process guided fuzzers.
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:doc:`FuzzingLLVM`
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Information on writing and using Fuzzers to find bugs in LLVM.
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========
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LLVM IR
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========
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:doc:`LLVM Language Reference Manual <LangRef>`
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Defines the LLVM intermediate representation and the assembly form of the
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different nodes.
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:doc:`InAlloca`
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Description of the ``inalloca`` argument attribute.
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:doc:`BitCodeFormat`
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This describes the file format and encoding used for LLVM "bc" files.
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:doc:`Machine IR (MIR) Format Reference Manual <MIRLangRef>`
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A reference manual for the MIR serialization format, which is used to test
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LLVM's code generation passes.
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:doc:`GlobalISel/index`
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This describes the prototype instruction selection replacement, GlobalISel.
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=====================
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Testing and Debugging
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=====================
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:doc:`LLVM Testing Infrastructure Guide <TestingGuide>`
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A reference manual for using the LLVM testing infrastructure.
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:doc:`TestSuiteGuide`
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Describes how to compile and run the test-suite benchmarks.
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:doc:`GwpAsan`
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A sampled heap memory error detection toolkit designed for production use.
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====
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XRay
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====
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:doc:`XRay`
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High-level documentation of how to use XRay in LLVM.
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:doc:`XRayExample`
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An example of how to debug an application with XRay.
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=================
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Additional Topics
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=================
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:doc:`FaultMaps`
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LLVM support for folding control flow into faulting machine instructions.
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:doc:`Atomics`
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Information about LLVM's concurrency model.
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:doc:`ExceptionHandling`
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This document describes the design and implementation of exception handling
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in LLVM.
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:doc:`Extensions`
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LLVM-specific extensions to tools and formats LLVM seeks compatibility with.
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:doc:`HowToSetUpLLVMStyleRTTI`
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How to make ``isa<>``, ``dyn_cast<>``, etc. available for clients of your
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class hierarchy.
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:doc:`BlockFrequencyTerminology`
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Provides information about terminology used in the ``BlockFrequencyInfo``
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analysis pass.
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:doc:`BranchWeightMetadata`
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Provides information about Branch Prediction Information.
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:doc:`GetElementPtr`
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Answers to some very frequent questions about LLVM's most frequently
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misunderstood instruction.
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:doc:`ScudoHardenedAllocator`
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A library that implements a security-hardened `malloc()`.
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:doc:`MemTagSanitizer`
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Security hardening for production code aiming to mitigate memory
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related vulnerabilities. Based on the Armv8.5-A Memory Tagging Extension.
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:doc:`Dependence Graphs <DependenceGraphs/index>`
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A description of the design of the various dependence graphs such as
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the DDG (Data Dependence Graph).
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:doc:`SpeculativeLoadHardening`
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A description of the Speculative Load Hardening mitigation for Spectre v1.
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:doc:`SegmentedStacks`
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This document describes segmented stacks and how they are used in LLVM.
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:doc:`MarkedUpDisassembly`
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This document describes the optional rich disassembly output syntax.
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:doc:`StackMaps`
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LLVM support for mapping instruction addresses to the location of
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values and allowing code to be patched.
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:doc:`Coroutines`
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LLVM support for coroutines.
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:doc:`PointerAuth`
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A description of pointer authentication, its LLVM IR representation, and its
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support in the backend.
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:doc:`YamlIO`
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A reference guide for using LLVM's YAML I/O library.
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:doc:`ConvergenceAndUniformity`
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A description of uniformity analysis in the presence of irreducible
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control flow, and its implementation.
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