[clang] [CIR] Function type return type improvements (PR #128787)

[David Olsen via cfe-commits]

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@@ -424,6 +424,10 @@ LogicalResult cir::FuncOp::verifyType() {
   if (!isa<cir::FuncType>(type))
     return emitOpError("requires '" + getFunctionTypeAttrName().str() +
                        "' attribute of function type");
+  if (auto rt = type.getReturnTypes();
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dkolsen-pgi wrote:

> `getFunctionType` already gives us a `cir::FuncType`, so an `isa` will always be true, correct?

Correct.  I just noticed that myself, as I was looking at this function more closely.

In the incubator, this function has three checks.  The first is a tautology, because it is checking if a `cir::FuncType` `isa` `cir::FuncType`.  The second, which I had not upstreamed yet, is wrong.  It checks that an ellipsis is not the only parameter, but functions with only an ellipsis are allowed in C++.  The third check, the one added in this PR, that there isn't an explicit `void` return type, is redundant, because that is already checked in `FuncType::verify`.

It doesn't look like `FuncOp::verifyType` is called from anywhere (even in the incubator), and it doesn't do anything useful.  So rather than adding a check for `rt.size() < 2` to the function, I will look into getting rid of it entirely.


https://github.com/llvm/llvm-project/pull/128787