[clang] [llvm] [AArch64] Add ability to list extensions enabled for a target (PR #95805)

[Tomas Matheson via cfe-commits]

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@@ -161,6 +162,39 @@ static int PrintSupportedExtensions(std::string TargetStr) {
   return 0;
 }
 
+static int PrintEnabledExtensions(const TargetOptions& TargetOpts) {
+  std::string Error;
+  const llvm::Target *TheTarget =
+      llvm::TargetRegistry::lookupTarget(TargetOpts.Triple, Error);
+  if (!TheTarget) {
+    llvm::errs() << Error;
+    return 1;
+  }
+
+  llvm::TargetOptions BackendOptions;
+  std::string FeaturesStr = llvm::join(TargetOpts.FeaturesAsWritten, ",");
+  std::unique_ptr<llvm::TargetMachine> TheTargetMachine(
+      TheTarget->createTargetMachine(TargetOpts.Triple, TargetOpts.CPU, FeaturesStr, BackendOptions, std::nullopt));
+  const llvm::Triple &MachineTriple = TheTargetMachine->getTargetTriple();
+  const llvm::MCSubtargetInfo *MCInfo = TheTargetMachine->getMCSubtargetInfo();
+  const std::vector<llvm::SubtargetFeatureKV> Features =
+    MCInfo->getEnabledProcessorFeatures();
+
+  std::vector<llvm::StringRef> EnabledFeatureNames;
+  for (const llvm::SubtargetFeatureKV &feature : Features)
+    EnabledFeatureNames.push_back(feature.Key);
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tmatheson-arm wrote:

Maybe we shouldn't throw away the type information in `llvm::SubtargetFeatureKV` before `printEnabledExtensions`. It is not clear what `EnabledFeatureNames` contains, since it is just a vector of strings. i.e. are they internal names, extension names, subtarget feature names, etc.

https://github.com/llvm/llvm-project/pull/95805