Simon Pilgrim 167af1bafb [SelectionDAG] Add icmp UNDEF handling to SelectionDAG::FoldSetCC ...

First half of PR40800, this patch adds DAG undef handling to icmp instructions to match the behaviour in llvm::ConstantFoldCompareInstruction and SimplifyICmpInst, this permits constant folding of vector comparisons where some elements had been reduced to UNDEF (by SimplifyDemandedVectorElts etc.).

This involved a lot of tweaking to reduced tests as bugpoint loves to reduce icmp arguments to undef........

Differential Revision: https://reviews.llvm.org/D59363

llvm-svn: 356938

2019-03-25 18:51:57 +00:00

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