[clang] [clang] Fix for Assertion `(T->hasSignedIntegerRepresentation() || T->isSignedFixedPointType()) && "Unexpected signed integer or fixed point type"' failed. (PR #195945)

[via cfe-commits]

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@@ -17331,13 +17314,20 @@ ExprResult Sema::BuildVAArgExpr(SourceLocation BuiltinLoc,
       if (!PromoteType.isNull() && !UnderlyingType->isBooleanType() &&
           PromoteType->isUnsignedIntegerType() !=
               UnderlyingType->isUnsignedIntegerType()) {
-        UnderlyingType =
-            UnderlyingType->isUnsignedIntegerType()
-                ? Context.getCorrespondingSignedType(UnderlyingType)
-                : Context.getCorrespondingUnsignedType(UnderlyingType);
-        if (Context.typesAreCompatible(PromoteType, UnderlyingType,
-                                       /*CompareUnqualified*/ true))
-          PromoteType = QualType();
+
+        // Because char16_t and char32_t have no corresponding signed type,
+        // calling getCorrespondingSignedType on them would assert. Guard
+        // against this.
+        const auto *BT = UnderlyingType->getAs<BuiltinType>();
+        if (!BT || (BT->getKind() != BuiltinType::Char16 &&
+                    BT->getKind() != BuiltinType::Char32)) {
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Sirraide wrote:

This means we’re not doing any promotion if the type is `char16_t`/`char32_t`, which I don’t think is right, but @AaronBallman probably knows that better than me.

Also, I think this change should come with a codegen test to make sure we actually try to extract the right type from the va_list.

https://github.com/llvm/llvm-project/pull/195945