[clang] [CIR] Add proper handling for no prototype function calls (PR #150553)

[Sirui Mu via cfe-commits]

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@@ -1729,6 +1783,34 @@ cir::FuncOp CIRGenModule::getOrCreateCIRFunction(
       invalidLoc ? theModule->getLoc() : getLoc(funcDecl->getSourceRange()),
       mangledName, mlir::cast<cir::FuncType>(funcType), funcDecl);
 
+  // If we already created a function with the same mangled name (but different
+  // type) before, take its name and add it to the list of functions to be
+  // replaced with F at the end of CodeGen.
+  //
+  // This happens if there is a prototype for a function (e.g. "int f()") and
+  // then a definition of a different type (e.g. "int f(int x)").
+  if (entry) {
+
+    // Fetch a generic symbol-defining operation and its uses.
+    auto symbolOp = mlir::cast<mlir::SymbolOpInterface>(entry);
+
+    // TODO(cir): When can this symbol be something other than a function?
+    if (!isa<cir::FuncOp>(entry))
+      errorNYI(d->getSourceRange(), "getOrCreateCIRFunction: non-FuncOp");
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Lancern wrote:

Is this branch ever possible?

https://github.com/llvm/llvm-project/pull/150553