[llvm] [compiler-rt] [clang] [AArch64][SME] Add support for sme-fa64 (PR #70809)

[Sander de Smalen via cfe-commits]

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@@ -508,6 +508,9 @@ def FeatureSMEI16I64 : SubtargetFeature<"sme-i16i64", "HasSMEI16I64", "true",
 def FeatureSMEF16F16 : SubtargetFeature<"sme-f16f16", "HasSMEF16F16", "true",
   "Enable SME2.1 non-widening Float16 instructions (FEAT_SME_F16F16)", []>;
 
+def FeatureSMEFA64 : SubtargetFeature<"sme-fa64", "HasSMEFA64", "true",
+  "Enable the full A64 instruction set in SVE streaming mode (FEAT_SME_FA64)", [FeatureSVE2, FeatureNEON]>;
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sdesmalen-arm wrote:

I'm not sure if we should imply these features, because `sme-fa64` will always be used in conjunction with SME.
We could choose to implement this as a feature that does not actually enable/imply any other features, but instead just changes the behaviour when a function is run in streaming-SVE mode, in the sense that the compiler can use NEON/Full SVE instructions.

https://github.com/llvm/llvm-project/pull/70809