[clang] [CIR] Implement folder for VecTernaryOp (PR #142946)

[Andy Kaylor via cfe-commits]

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@@ -138,10 +138,10 @@ void CIRCanonicalizePass::runOnOperation() {
     assert(!cir::MissingFeatures::complexRealOp());
     assert(!cir::MissingFeatures::complexImagOp());
     assert(!cir::MissingFeatures::callOp());
-    // CastOp, UnaryOp, VecExtractOp and VecShuffleDynamicOp are here to perform
-    // a manual `fold` in applyOpPatternsGreedily.
+    // CastOp, UnaryOp, VecExtractOp, VecShuffleDynamicOp and VecTernaryOp are
+    // here to perform a manual `fold` in applyOpPatternsGreedily.
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andykaylor wrote:

That's not really necessary. I think we've passed the point where anyone is going to be checking each one to see why it's here. Also, some operations may be handled explicitly and also have a folder.

https://github.com/llvm/llvm-project/pull/142946