[llvm] [InstCombine] Enable select freeze poison folding when storing value (PR #129776)

[John McIver via llvm-commits]

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@@ -4842,8 +4847,11 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
 
   Constant *C;
   if (match(Op0, m_Constant(C)) && C->containsUndefOrPoisonElement()) {
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jmciver wrote:

Thanks for pointing out the miscompilation!

The reason I did not place this logic into `InstCombinerImpl::visitSelect` was the canonical form produced by `InstCombinerImpl::visitFreeze` occurs first and thus ruins the match on freeze poison when visitation is performed on the select instruction.

I experimented a bit and derived a two match expression in the lambda function.

Added basic vector tests.

https://github.com/llvm/llvm-project/pull/129776