[clang] [Clang][RISCV] Recognize unsupport target feature by supporting isValidFeatureName (PR #106495)

[Craig Topper via cfe-commits]

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@@ -2993,10 +2993,17 @@ bool Sema::checkTargetAttr(SourceLocation LiteralLoc, StringRef AttrStr) {
     return Diag(LiteralLoc, diag::warn_unsupported_target_attribute)
            << Unknown << Tune << ParsedAttrs.Tune << Target;
 
-  if (Context.getTargetInfo().getTriple().isRISCV() &&
-      ParsedAttrs.Duplicate != "")
-    return Diag(LiteralLoc, diag::err_duplicate_target_attribute)
-           << Duplicate << None << ParsedAttrs.Duplicate << Target;
+  if (Context.getTargetInfo().getTriple().isRISCV()) {
+    if (ParsedAttrs.Duplicate != "")
+      return Diag(LiteralLoc, diag::err_duplicate_target_attribute)
+             << Duplicate << None << ParsedAttrs.Duplicate << Target;
+    for (const auto &Feature : ParsedAttrs.Features) {
+      auto CurFeature = StringRef(Feature);
+      if (!CurFeature.starts_with("+") && !CurFeature.starts_with("-"))
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topperc wrote:

Use `'+'` and `'-'` instead of `"+"` and `"-"` since we're checking a single character.

https://github.com/llvm/llvm-project/pull/106495