[clang] [HLSL] Diagnose dynamic indexing of struct arrays for resource access (PR #187132)

[Helena Kotas via cfe-commits]

================
@@ -3068,6 +3068,50 @@ void SemaHLSL::ActOnEndOfTranslationUnit(TranslationUnitDecl *TU) {
   diagnoseAvailabilityViolations(TU);
 }
 
+// For resource member access through a global struct array, verify that the
+// array index selecting the struct element is a constant integer expression.
+// Returns false if the member expression is invalid.
+bool SemaHLSL::ActOnResourceMemberAccessExpr(MemberExpr *ME) {
+  assert((ME->getType()->isHLSLResourceRecord() ||
+          ME->getType()->isHLSLResourceRecordArray()) &&
+         "expected member expr to have resource record type or array of them");
+
+  // Walk the AST from MemberExpr to the VarDecl of the parent struct instance
+  // and take note of any non-constant array indexing along the way. If the
+  // VarDecl we find is a global variable, report error if there was any
+  // non-constant array index in the resource member access along the way.
+  const Expr *NonConstIndexExpr = nullptr;
+  const Expr *E = ME->getBase();
+  while (E) {
+    if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
+      if (!NonConstIndexExpr)
----------------
hekota wrote:

Yes, `DeclRefExpr` can appear first and very often does - anytime the member access chain does not go through any array indexing. And in that case `NonConstIndexExpr` is correctly nullptr because there was no non-constant indexing happening.

https://github.com/llvm/llvm-project/pull/187132