[all-commits] [llvm/llvm-project] 40f0f7: [FMV][AArch64] Unify features ssbs and ssbs2. (#11...

[Alexandros Lamprineas via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 40f0f7b4ec3eea4827fa3e54153ff722b5842ea1
      https://github.com/llvm/llvm-project/commit/40f0f7b4ec3eea4827fa3e54153ff722b5842ea1
  Author: Alexandros Lamprineas <alexandros.lamprineas at arm.com>
  Date:   2024-10-07 (Mon, 07 Oct 2024)

  Changed paths:
    M clang/test/CodeGen/aarch64-fmv-dependencies.c
    M clang/test/CodeGen/attr-target-version.c
    M clang/test/CodeGenCXX/attr-target-clones-aarch64.cpp
    M clang/test/Sema/attr-target-clones-aarch64.c
    M clang/test/SemaCXX/attr-target-version.cpp
    M compiler-rt/lib/builtins/cpu_model/AArch64CPUFeatures.inc
    M compiler-rt/lib/builtins/cpu_model/aarch64/fmv/apple.inc
    M compiler-rt/lib/builtins/cpu_model/aarch64/fmv/mrs.inc
    M llvm/include/llvm/TargetParser/AArch64CPUFeatures.inc
    M llvm/lib/Target/AArch64/AArch64FMV.td

  Log Message:
  -----------
  [FMV][AArch64] Unify features ssbs and ssbs2. (#110297)

According to https://developer.arm.com/documentation/102105/latest Arm
Architecture Reference Manual for A-profile architecture: Known issues

2.206 D22789
In section C5.2.25 "SSBS, Speculative Store Bypass Safe", under the
heading 'Configurations', the text that reads:

"This register is present only when FEAT_SSBS is implemented. Otherwise,
direct accesses to SSBS are UNDEFINED."

is changed to read:

"This register is present only when FEAT_SSBS2 is implemented.
Otherwise, direct accesses to SSBS are UNDEFINED."

This suggests that it's not worth splitting FEAT_SSBS2 from FEAT_SSBS in
the compiler, since FEAT_SSBS cannot be used for predicating the MRS/MSR
instructions. Those can access PSTATE.SSBS only when FEAT_SSBS2 is
available. Moreover, there are no hardware implementations which
implement FEAT_SSBS without FEAT_SSBS2, therefore unifying these
features in the specification should not be a regression for feature
detection.

Approved in ACLE as https://github.com/ARM-software/acle/pull/350



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