[llvm] [CombinerHelper]: Use undef for handling divisors of one (PR #91037)

[Matt Arsenault via llvm-commits]

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@@ -217,25 +217,66 @@ define <8 x i16> @pr38477(<8 x i16> %a0) {
 ;
 ; GISEL-LABEL: pr38477:
 ; GISEL:       // %bb.0:
-; GISEL-NEXT:    adrp x8, .LCPI5_3
-; GISEL-NEXT:    ldr q1, [x8, :lo12:.LCPI5_3]
-; GISEL-NEXT:    adrp x8, .LCPI5_2
-; GISEL-NEXT:    ldr q3, [x8, :lo12:.LCPI5_2]
-; GISEL-NEXT:    adrp x8, .LCPI5_0
-; GISEL-NEXT:    umull2 v2.4s, v0.8h, v1.8h
+; GISEL-NEXT:    mov w8, #4957 // =0x135d
+; GISEL-NEXT:    mov w9, #16385 // =0x4001
+; GISEL-NEXT:    fmov s1, w8
+; GISEL-NEXT:    mov w8, #57457 // =0xe071
+; GISEL-NEXT:    fmov s4, w9
+; GISEL-NEXT:    fmov s2, w8
+; GISEL-NEXT:    mov w8, #4103 // =0x1007
+; GISEL-NEXT:    mov w9, #35545 // =0x8ad9
+; GISEL-NEXT:    fmov s5, w9
+; GISEL-NEXT:    mov w9, #2048 // =0x800
+; GISEL-NEXT:    mov v1.h[1], v1.h[0]
+; GISEL-NEXT:    fmov s6, w9
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arsenm wrote:

This looks way worse 

https://github.com/llvm/llvm-project/pull/91037