[all-commits] [llvm/llvm-project] 52faad: [AArch64] Use Feature for A53 Erratum 835769 Fix

[Sam Elliott via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 52faad83c9f8732f433ff2e1f645649aa90d6c42
      https://github.com/llvm/llvm-project/commit/52faad83c9f8732f433ff2e1f645649aa90d6c42
  Author: Archibald Elliott <archibald.elliott at arm.com>
  Date:   2021-12-10 (Fri, 10 Dec 2021)

  Changed paths:
    M clang/lib/Driver/ToolChains/Arch/AArch64.cpp
    M clang/lib/Driver/ToolChains/Clang.cpp
    M clang/test/Driver/aarch64-fix-cortex-a53-835769.c
    M llvm/lib/Target/AArch64/AArch64.td
    M llvm/lib/Target/AArch64/AArch64A53Fix835769.cpp
    M llvm/lib/Target/AArch64/AArch64Subtarget.h
    M llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
    M llvm/test/CodeGen/AArch64/O0-pipeline.ll
    M llvm/test/CodeGen/AArch64/O3-pipeline.ll
    M llvm/test/CodeGen/AArch64/aarch64-fix-cortex-a53-835769.ll

  Log Message:
  -----------
  [AArch64] Use Feature for A53 Erratum 835769 Fix

When this pass was originally implemented, the fix pass was enabled
using a llvm command-line flag. This works fine, except in the case of
LTO, where the flag is not passed into the linker plugin in order to
enable the function pass in the LTO backend.

Now LTO exists, the expectation now is to use target features rather
than command-line arguments to control code generation, as this ensures
that different command-line arguments in different files are correctly
represented, and target-features always get to the LTO plugin as they
are encoded into LLVM IR.

The fall-out of this change is that the fix pass has to always be added
to the backend pass pipeline, so now it makes no changes if the function
does not have the right target feature to enable it. This should make a
minimal difference to compile time.

One advantage is it's now much easier to enable when compiling for a
Cortex-A53, as CPUs imply their own individual sets of target-features,
in a more fine-grained way. I haven't done this yet, but it is an
option, if the fix should be enabled in more places.

Existing tests of the user interface are unaffected, the changes are to
reflect that the argument is now turned into a target feature.

Reviewed By: tmatheson

Differential Revision: https://reviews.llvm.org/D114703