[llvm] [DAGCombiner] Freeze maybe poison operands when folding select to logic (PR #84924)

[Björn Pettersson via llvm-commits]

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@@ -295,22 +295,28 @@ define float @select_icmp_sle(i32 %x, i32 %y, float %a, float %b) {
 ; Test peephole optimizations for select.
 define zeroext i1 @select_opt1(i1 zeroext %c, i1 zeroext %a) {
 ; CHECK-LABEL: select_opt1
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bjope wrote:

I figure that these diffs are a bit annoying. But given that the AssertZext/AssertSext are handles as maybe producing poison we can't hoist the freeze above it. And then I think we lose the optimizations based on that the inputs are masked down to a single bit. But maybe this also kind of originates from CopyFromReg not being treated as an implicit FREEZE (at least if the arguments would have been marked as `noundef`).

https://github.com/llvm/llvm-project/pull/84924