[llvm] [InstCombine] Allow folding cross-lane operations into PHIs/selects (PR #164388)

[Benjamin Maxwell via llvm-commits]

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@@ -132,7 +132,7 @@ define float @test_select_frexp_fast_math_select(float %x, i1 %cond) {
 ; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
 ; CHECK-NEXT:    [[FREXP1:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
 ; CHECK-NEXT:    [[MANTISSA:%.*]] = extractvalue { float, i32 } [[FREXP1]], 0
-; CHECK-NEXT:    [[SELECT_FREXP:%.*]] = select nnan ninf nsz i1 [[COND]], float 5.000000e-01, float [[MANTISSA]]
+; CHECK-NEXT:    [[SELECT_FREXP:%.*]] = select i1 [[COND]], float 5.000000e-01, float [[MANTISSA]]
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MacDue wrote:

The FMFs end up getting dropped here as this was previously handled by `foldFrexpOfSelect`, but now the more general `FoldOpIntoSelect` handles it first. 

https://github.com/llvm/llvm-project/pull/164388