[llvm] [DAG] canCreateUndefOrPoison/isGuaranteedNotToBeUndefOrPoison - SCALAR_TO_VECTOR upper elements are poison (PR #217185)

[Simon Pilgrim via llvm-commits]

================
@@ -4906,16 +4906,17 @@ entry:
 define i32 @test_udot_v33i8_nomla(ptr nocapture readonly %a1) {
 ; CHECK-SD-LABEL: test_udot_v33i8_nomla:
 ; CHECK-SD:       // %bb.0: // %entry
-; CHECK-SD-NEXT:    ldr b1, [x0, #32]
+; CHECK-SD-NEXT:    ldrb w8, [x0, #32]
 ; CHECK-SD-NEXT:    ldp q3, q2, [x0]
 ; CHECK-SD-NEXT:    movi v0.2d, #0000000000000000
-; CHECK-SD-NEXT:    ushll v1.8h, v1.8b, #0
+; CHECK-SD-NEXT:    fmov s1, w8
----------------
RKSimon wrote:

You should probably update the SimplifyDemandedBits/SimplifyDemandedVectorElts cases as part of this patch as well.

https://github.com/llvm/llvm-project/pull/217185