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fuchsia / third_party / github.com / llvm / llvm-project / 6716e7868ec31668f8200e05d8550d3099b2c697
commit6716e7868ec31668f8200e05d8550d3099b2c697[log] [tgz]
authorSjoerd Meijer <sjoerd.meijer@arm.com>Tue Aug 11 15:48:29 2020 +0100
committerSjoerd Meijer <sjoerd.meijer@arm.com>Wed Aug 12 09:32:26 2020 +0100
treee6ff73abbcd8c593318277ba043ca43ce1f79e8d
parentac37afa650271d8366b706d79ff8e217fc624cbb [diff]
[ARM][MVE] tail-predication: overflow checks for backedge taken count.

This pick ups the work on the overflow checks for get.active.lane.mask,
which ensure that it is safe to insert the VCTP intrinisc that enables
tail-predication. For a 2d auto-correlation kernel and its inner loop j:

  M = Size - i;
  for (j = 0; j < M; j++)
    Sum += Input[j] * Input[j+i];

For this inner loop, the SCEV backedge taken count (BTC) expression is:

  (-1 + (sext i16 %Size to i32)),+,-1}<nw><%for.body>

and LoopUtil cannotBeMaxInLoop couldn't calculate a bound on this, thus "BTC
cannot be max" could not be determined. So overflow behaviour had to be assumed
in the loop tripcount expression that uses the BTC. As a result
tail-predication had to be forced (with an option) for this case.

This change solves that by using ScalarEvolution's helper
getConstantMaxBackedgeTakenCount which is able to determine the range of BTC,
thus can determine it is safe, so that we no longer need to force tail-predication
as reflected in the changed test cases.

Differential Revision: https://reviews.llvm.org/D85737
3 files changed
tree: e6ff73abbcd8c593318277ba043ca43ce1f79e8d
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. flang/
  6. libc/
  7. libclc/
  8. libcxx/
  9. libcxxabi/
  10. libunwind/
  11. lld/
  12. lldb/
  13. llvm/
  14. mlir/
  15. openmp/
  16. parallel-libs/
  17. polly/
  18. pstl/
  19. utils/
  20. .arcconfig
  21. .arclint
  22. .clang-format
  23. .clang-tidy
  24. .git-blame-ignore-revs
  25. .gitignore
  26. CONTRIBUTING.md
  27. README.md
README.md

The LLVM Compiler Infrastructure

This directory and its sub-directories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.

Getting Started with the LLVM System

Taken from https://llvm.org/docs/GettingStarted.html.

Overview

Welcome to the LLVM project!

The LLVM project has multiple components. The core of the project is itself called “LLVM”. This contains all of the tools, libraries, and header files needed to process intermediate representations and converts it into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.

C-like languages use the Clang front end. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.

Other components include: the libc++ C++ standard library, the LLD linker, and more.

Getting the Source Code and Building LLVM

The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.

This is an example work-flow and configuration to get and build the LLVM source:

  1. Checkout LLVM (including related sub-projects like Clang):

    • git clone https://github.com/llvm/llvm-project.git

    • Or, on windows, git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git

  2. Configure and build LLVM and Clang:

    • cd llvm-project

    • mkdir build

    • cd build

    • cmake -G <generator> [options] ../llvm

      Some common build system generators are:

      • Ninja --- for generating Ninja build files. Most llvm developers use Ninja.
      • Unix Makefiles --- for generating make-compatible parallel makefiles.
      • Visual Studio --- for generating Visual Studio projects and solutions.
      • Xcode --- for generating Xcode projects.

      Some Common options:

      • -DLLVM_ENABLE_PROJECTS='...' --- semicolon-separated list of the LLVM sub-projects you'd like to additionally build. Can include any of: clang, clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld, polly, or debuginfo-tests.

        For example, to build LLVM, Clang, libcxx, and libcxxabi, use -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi".

      • -DCMAKE_INSTALL_PREFIX=directory --- Specify for directory the full path name of where you want the LLVM tools and libraries to be installed (default /usr/local).

      • -DCMAKE_BUILD_TYPE=type --- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug.

      • -DLLVM_ENABLE_ASSERTIONS=On --- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).

    • cmake --build . [-- [options] <target>] or your build system specified above directly.

      • The default target (i.e. ninja or make) will build all of LLVM.

      • The check-all target (i.e. ninja check-all) will run the regression tests to ensure everything is in working order.

      • CMake will generate targets for each tool and library, and most LLVM sub-projects generate their own check-<project> target.

      • Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for make, use the option -j NNN, where NNN is the number of parallel jobs, e.g. the number of CPUs you have.

    • For more information see CMake

Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.