[llvm] [LegalizeTypes] Use VP_AND and VP_SHL/VP_SRA to promote operands fo VP arithmetic. (PR #92799)

[Philip Reames via llvm-commits]

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@@ -10,10 +10,9 @@ define <8 x i7> @vdivu_vv_v8i7(<8 x i7> %va, <8 x i7> %b, <8 x i1> %m, i32 zeroe
 ; CHECK-LABEL: vdivu_vv_v8i7:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    li a1, 127
-; CHECK-NEXT:    vsetivli zero, 8, e8, mf2, ta, ma
-; CHECK-NEXT:    vand.vx v9, v9, a1
-; CHECK-NEXT:    vand.vx v8, v8, a1
 ; CHECK-NEXT:    vsetvli zero, a0, e8, mf2, ta, ma
+; CHECK-NEXT:    vand.vx v9, v9, a1, v0.t
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preames wrote:

In this case, the use of the vp_and appears to be a semantic change.  The masked off lines were previously legalized, and now aren't.  Which is the expected behavior?  

Setting the correctness aside for a moment, I'd expect the unmasked legalization (using a temporary register) to frequently perform better.  Where's the right place to account for that?  Probably not during legalization per se, but these look like perf regressions in practice to me.  Do we care?

https://github.com/llvm/llvm-project/pull/92799