[clang] [CIR] Upstream global variable replacement (PR #184686)

[Erich Keane via cfe-commits]

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@@ -674,6 +674,49 @@ static void setLinkageForGV(cir::GlobalOp &gv, const NamedDecl *nd) {
     gv.setLinkage(cir::GlobalLinkageKind::ExternalWeakLinkage);
 }
 
+// We want to replace a global value, but because of CIR's typed pointers,
+// we need to update the existing uses to reflect the new type, not just replace
+// them directly.
+void CIRGenModule::replaceGlobal(cir::GlobalOp oldGV, cir::GlobalOp newGV) {
+  assert(oldGV.getSymName() == newGV.getSymName() && "symbol names must match");
+
+  mlir::Type oldTy = oldGV.getSymType();
+  mlir::Type newTy = newGV.getSymType();
+
+  assert(!cir::MissingFeatures::addressSpace());
+
+  // If the type didn't change, why are we here?
+  assert(oldTy != newTy && "expected type change in replaceGlobal");
+
+  // Otherwise, visit all uses and add handling to fix up the types.
+  std::optional<mlir::SymbolTable::UseRange> oldSymUses =
+      oldGV.getSymbolUses(theModule);
+  if (oldSymUses) {
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erichkeane wrote:

This `if` is unnecessary, thanks to the range-for.

https://github.com/llvm/llvm-project/pull/184686