[clang] [CIR] Upstream emitAndUpdateRetAlloca (PR #129933)

[Andy Kaylor via cfe-commits]

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@@ -13,8 +13,9 @@ void voidret() { return; }
 
 int intfunc() { return 42; }
 // CHECK: cir.func @intfunc() -> !cir.int<s, 32> {
-// CHECK:   %0 = cir.const #cir.int<42> : !cir.int<s, 32>
-// CHECK:   cir.return %0 : !cir.int<s, 32>
+// CHECK:   %0 = cir.alloca !cir.int<s, 32>, !cir.ptr<!cir.int<s, 32>>, ["__retval"] {alignment = 4 : i64}
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andykaylor wrote:

I realize you were just following the style of the existing test, but in general it's preferable to use a substitution variable for IR identifiers that need to be matched or omit them from the check if they don't need to be matched.
```suggestion
// CHECK:   %[[RET_ALLOCA:.*]] = cir.alloca !cir.int<s, 32>, !cir.ptr<!cir.int<s, 32>>, ["__retval"] {alignment = 4 : i64}
```

https://github.com/llvm/llvm-project/pull/129933