[llvm] [VPlan] Expand VPBlendRecipe earlier in simplifyBlends (PR #171851)

[Florian Hahn via llvm-commits]

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@@ -686,253 +686,13 @@ exit:
 ; Test for https://github.com/llvm/llvm-project/issues/129236.
 define i32 @cost_ashr_with_op_known_invariant_via_scev(i8 %a) {
 ; CHECK-LABEL: @cost_ashr_with_op_known_invariant_via_scev(
-; CHECK-NEXT:  iter.check:
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fhahn wrote:

I had a look at these changes, and I think the root cause is not that we can simplify the selects/masks here better than previously, it is just that with the new form we run simplifyRecipes one more time, which allows removing a trivial `select %cond, poison, zero`.

(The tes case in general isn't really great, with those trivially selects)

https://github.com/llvm/llvm-project/pull/171851