[llvm] [RISCV] Add getFeaturesForCPU function support (PR #83269)

[Craig Topper via llvm-commits]

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@@ -95,5 +96,31 @@ void fillValidTuneCPUArchList(SmallVectorImpl<StringRef> &Values, bool IsRV64) {
 #include "llvm/TargetParser/RISCVTargetParserDef.inc"
 }
 
+void getFeaturesForCPU(StringRef CPU,
+                       SmallVectorImpl<std::string> &EnabledFeatures,
+                       bool NeedPlus) {
+  StringRef MarchFromCPU = llvm::RISCV::getMArchFromMcpu(CPU);
+  if (MarchFromCPU == "")
+    return;
+
+  EnabledFeatures.clear();
+  auto RII = RISCVISAInfo::parseArchString(
+      MarchFromCPU, /* EnableExperimentalExtension */ true);
+
+  if (llvm::errorToBool(RII.takeError()))
+    return;
+
+  std::vector<std::string> FeatStrings =
+      (*RII)->toFeatures(/* AddAllExtensions */ true);
+  for (const auto &F : FeatStrings) {
+    if (F[0] == '-')
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topperc wrote:

Why pass AddAllExtensions=true if you're going to skip the '-' ones?

https://github.com/llvm/llvm-project/pull/83269