[llvm] Improve diagnostic for malformed constant vectors (PR #216253)

[via llvm-commits]

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@@ -4275,6 +4275,12 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
     // ValID ::= '<' ConstVector '>'         --> Vector.
     // ValID ::= '<' '{' ConstVector '}' '>' --> Packed Struct.
     Lex.Lex();
+
+    // guard constant vector elements must begin with a type.
+    if (Lex.getKind() == lltok::APSInt || Lex.getKind() == lltok::Type)
+      return error(Lex.getLoc(),
+                   "constant vector elements must begin with a type");
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zhangweize9-cyber wrote:

Because there's already a case branch within the function body, writing a condition here won't trigger the logic you wrote.

https://github.com/llvm/llvm-project/pull/216253