[clang] [CIR] Update uses of no-prototype GetGlobalOp (PR #193868)

[Erich Keane via cfe-commits]

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@@ -1816,9 +1816,23 @@ void CIRGenModule::replaceUsesOfNonProtoTypeWithRealFunction(
       noProtoCallOp.erase();
     } else if (auto getGlobalOp =
                    mlir::dyn_cast<cir::GetGlobalOp>(use.getUser())) {
-      // Replace type
-      getGlobalOp.getAddr().setType(
-          cir::PointerType::get(newFn.getFunctionType()));
+      // The GetGlobal was emitted with the no-proto FuncType. Uses of this
+      // operation (cir.store, cir.cast) were built for that pointer type. When
+      // we re-type the result to the real FuncType, we need to add a bit the
+      // old pointer type so those uses are still valid. This can lead to
+      // some redundant bitcast chains, but those will be cleaned up by the
+      // canonicalizer.
+      mlir::Value res = getGlobalOp.getAddr();
+      const mlir::Type oldResTy = res.getType();
+      const auto newPtrTy = cir::PointerType::get(newFn.getFunctionType());
+      res.setType(newPtrTy);
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erichkeane wrote:

can we/should we move 'set type' inside the '!=' branch below? 

https://github.com/llvm/llvm-project/pull/193868