[clang] [Clang] Fix cluster_dims thread block limit checks (PR #230186)

[Petar Jovanovic via cfe-commits]

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@@ -6180,10 +6180,13 @@ static void handleLaunchBoundsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
                         AL.getNumArgs() > 2 ? AL.getArgAsExpr(2) : nullptr);
 }
 
-static std::pair<Expr *, int>
+static std::pair<Expr *, uint64_t>
 makeClusterDimsArgExpr(Sema &S, Expr *E, const CUDAClusterDimsAttr &AL,
                        const unsigned Idx) {
-  if (!E || S.DiagnoseUnexpandedParameterPack(E))
+  if (!E)
+    return {nullptr, 1};
+
+  if (S.DiagnoseUnexpandedParameterPack(E))
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petar-jovanovic wrote:

> I meant to ask the `!E` case, since it was `{}` before, but now it is `{nullptr, 1}`.

I was responding to your comment on !E. Just follow the previous path with cluster_dims(15,15) and you will see that we would return wrong result. !E is not a failure path; it represents an omitted dimension. Since FlatDim is computed as a product, an omitted dimension must contribute 1, not 0. Previously cluster_dims(15, 15) was evaluated as 15 * 15 * 0, which disabled the flat-size check and incorrectly accepted a 225-block cluster. The change only fixes that value; the Expr * remains nullptr and the existing caller logic is unchanged.

https://github.com/llvm/llvm-project/pull/230186