[clang] [CIR] Implement simple folding for unary operations (PR #174882)

[Erich Keane via cfe-commits]

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@@ -2479,6 +2479,39 @@ OpFoldResult cir::UnaryOp::fold(FoldAdaptor adaptor) {
       if (isBoolNot(previous))
         return previous.getInput();
 
+  // Fold constant unary operations.
+  if (auto srcConst = getInput().getDefiningOp<cir::ConstantOp>()) {
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erichkeane wrote:

I might suggest we do a `TypeSwitch` if we're doing something like that.  That said, WHICH direction we go (switch on kind, then type, vs type then kind) doesn't seem particularly motivated in 1 way or the other?

https://github.com/llvm/llvm-project/pull/174882