[all-commits] [llvm/llvm-project] 7954a0: [Clang] Enable -fpointer-tbaa by default. (#117244)

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7954a0514ba7de40dba6c598af830fd1b7a8bf0c
      https://github.com/llvm/llvm-project/commit/7954a0514ba7de40dba6c598af830fd1b7a8bf0c
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2024-12-04 (Wed, 04 Dec 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/CodeGenOptions.def
    M clang/include/clang/Driver/Options.td
    M clang/lib/Driver/ToolChains/Clang.cpp
    M clang/test/CodeGen/attr-counted-by.c
    M clang/test/CodeGen/tbaa-pointers.c
    M clang/test/CodeGen/tbaa-reference.cpp
    M clang/test/CodeGenCXX/template-instantiation.cpp
    M clang/test/CodeGenOpenCL/amdgpu-enqueue-kernel.cl
    M clang/test/OpenMP/nvptx_target_parallel_reduction_codegen_tbaa_PR46146.cpp
    M clang/test/OpenMP/taskloop_strictmodifier_codegen.cpp
    M clang/unittests/CodeGen/TBAAMetadataTest.cpp

  Log Message:
  -----------
  [Clang] Enable -fpointer-tbaa by default. (#117244)

Support for more precise TBAA metadata has been added a while ago
(behind the -fpointer-tbaa flag). The more precise TBAA metadata allows
treating accesses of different pointer types as no-alias.

This helps to remove more redundant loads and stores in a number of
workloads.

Some highlights on the impact across llvm-test-suite's MultiSource,
SPEC2006 & SPEC2017 include:
 * +2% more NoAlias results for memory accesses
 * +3% more stores removed by DSE,
 * +4% more loops vectorized.

This closes a relatively big gap to GCC, which has been supporting
disambiguating based on pointer types for a long time.
(https://clang.godbolt.org/z/K7Wbhrz4q)

Pointer-TBAA support for pointers to builtin types has been added in
https://github.com/llvm/llvm-project/pull/76612.

Support for user-defined types has been added in
https://github.com/llvm/llvm-project/pull/110569.

There are 2 recent PRs with bug fixes for special cases uncovered during
testing:
 * https://github.com/llvm/llvm-project/pull/116991
 * https://github.com/llvm/llvm-project/pull/116596

PR: https://github.com/llvm/llvm-project/pull/117244



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