[clang] [CIR][CodeGen] Eliminate unnecessary __retval alloca for simple returns (PR #186320)

[Andy Kaylor via cfe-commits]

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@@ -585,6 +585,31 @@ mlir::LogicalResult CIRGenFunction::emitDeclStmt(const DeclStmt &s) {
   return mlir::success();
 }
 
+static cir::StoreOp findDominatingStoreToReturnValue(CIRGenFunction &cgf) {
+  mlir::Block *currentBlock = cgf.getBuilder().getInsertionBlock();
+  if (!currentBlock || currentBlock->empty())
+    return nullptr;
+
+  if (!cgf.fnRetAlloca)
+    return nullptr;
+
+  mlir::Value retAlloca = *cgf.fnRetAlloca;
+
+  for (auto &op : llvm::reverse(*currentBlock)) {
+    if (auto storeOp = dyn_cast<cir::StoreOp>(op)) {
+      if (storeOp.getAddr() == retAlloca) {
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andykaylor wrote:

Braces aren't needed here.

https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements

https://github.com/llvm/llvm-project/pull/186320