[clang] [RISCV] Overwrite cpu target features for full arch string in target attribute (PR #77426)

[Craig Topper via cfe-commits]

================
@@ -281,10 +248,28 @@ bool RISCVTargetInfo::initFeatureMap(
     Features["32bit"] = true;
   }
 
-  std::vector<std::string> NewFeaturesVec =
-      resolveTargetAttrOverride(FeaturesVec, XLen);
+  // If a target attribute specified a full arch string, override all the ISA
+  // extension target features.
+  const auto I = llvm::find(FeaturesVec, "__RISCV_TargetAttrNeedOverride");
+  if (I != FeaturesVec.end()) {
+    std::vector<std::string> OverrideFeatures =
+        std::vector(std::next(I), FeaturesVec.end());
+
+    // Add back any non ISA extension features, e.g. +relax.
+    auto IsNonISAExtFeature = [](const std::string &Feature) {
+      assert(Feature.size() > 1 && (Feature[0] == '+' || Feature[0] == '-'));
+      std::string Ext = Feature.substr(1); // drop the +/-
----------------
topperc wrote:

StringRef Ext = Feature.drop_front(1)

https://github.com/llvm/llvm-project/pull/77426