[clang] [compiler-rt] [llvm] [FMV] Remove useless features according the latest ACLE spec. (PR #88965)

[Andrew Carlotti via cfe-commits]

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@@ -67,57 +67,42 @@ enum CPUFeatures {
   FEAT_FP,
   FEAT_SIMD,
   FEAT_CRC,
-  FEAT_SHA1,
   FEAT_SHA2,
   FEAT_SHA3,
   FEAT_AES,
-  FEAT_PMULL,
   FEAT_FP16,
-  FEAT_DIT,
   FEAT_DPB,
   FEAT_DPB2,
   FEAT_JSCVT,
   FEAT_FCMA,
   FEAT_RCPC,
   FEAT_RCPC2,
   FEAT_FRINTTS,
-  FEAT_DGH,
   FEAT_I8MM,
   FEAT_BF16,
-  FEAT_EBF16,
   FEAT_RPRES,
   FEAT_SVE,
-  FEAT_SVE_BF16,
-  FEAT_SVE_EBF16,
-  FEAT_SVE_I8MM,
   FEAT_SVE_F32MM,
   FEAT_SVE_F64MM,
   FEAT_SVE2,
   FEAT_SVE_AES,
-  FEAT_SVE_PMULL128,
   FEAT_SVE_BITPERM,
   FEAT_SVE_SHA3,
   FEAT_SVE_SM4,
   FEAT_SME,
   FEAT_MEMTAG,
-  FEAT_MEMTAG2,
-  FEAT_MEMTAG3,
   FEAT_SB,
   FEAT_PREDRES,
   FEAT_SSBS,
-  FEAT_SSBS2,
-  FEAT_BTI,
   FEAT_LS64,
-  FEAT_LS64_V,
-  FEAT_LS64_ACCDATA,
   FEAT_WFXT,
   FEAT_SME_F64,
   FEAT_SME_I64,
   FEAT_SME2,
   FEAT_RCPC3,
   FEAT_MOPS,
   FEAT_MAX,
-  FEAT_EXT = 62, // Reserved to indicate presence of additional features field
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andrewcarlotti wrote:

For the ifunc implementation to work reliably, then the relevant parts of compiler-rt (or libgcc for the GCC implementation) should be statically linked. Otherwise there's a possibility that the symbols aren't actually loaded yet when the ifunc resolver is run. So there should be no exposed ABI in the context of FMV.

As for other uses, we haven't agreed to freeze this as part of the ABI yet, but we are giving this possibility some consideration in designing the FMV resolver.

https://github.com/llvm/llvm-project/pull/88965