[clang] [llvm] [AArch64][FMV] Add missing feature dependencies and detect at runtime. (PR #119231)

[Sander de Smalen via cfe-commits]

================
@@ -61,13 +61,13 @@ unsigned AArch64::getFMVPriority(ArrayRef<StringRef> 
Features) {
   return Priority + MaxFMVPriority * NumFeatures;
 }
 
-uint64_t AArch64::getCpuSupportsMask(ArrayRef<StringRef> FeatureStrs) {
-  uint64_t FeaturesMask = 0;
-  for (const StringRef &FeatureStr : FeatureStrs) {
-    if (auto Ext = parseFMVExtension(FeatureStr))
-      FeaturesMask |= (1ULL << Ext->Bit);
-  }
-  return FeaturesMask;
+uint64_t AArch64::getCpuSupportsMask(ArrayRef<StringRef> Features) {
+  ExtensionSet FeatureBits;
+  for (StringRef Feature : Features)
+    if (auto Ext = parseFMVExtension(Feature))
+      if (Ext->ID)
+        FeatureBits.enable(*Ext->ID);
----------------
sdesmalen-arm wrote:

Thanks. Could you make this more explicit in the documentation, i.e. that 
`AArch64::CPUFeatures` is a bitmask of features used by the FMV mechanism to 
test whether a certain feature is enabled at runtime?

https://github.com/llvm/llvm-project/pull/119231
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