[llvm-bugs] [Bug 39637] New: [X86] Failure to combine vpmovzxbw with a v16i16->v16i8 truncate implemented with extract+packuswb

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39637

            Bug ID: 39637
           Summary: [X86] Failure to combine vpmovzxbw with a
                    v16i16->v16i8 truncate implemented with
                    extract+packuswb
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: craig.topper at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

This code from combine-udiv.ll shows a packuswb followed by a vpmovzxbw. These
instructions should cancel each other out.

; AVX2-LABEL: combine_vec_udiv_nonuniform4:
; AVX2:       # %bb.0:
; AVX2-NEXT:    vpmovzxbw {{.*#+}} ymm1 =
xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero,xmm0[4],zero,xmm0[5],zero,xmm0[6],zero,xmm0[7],zero,xmm0[8],zero,xmm0[9],zero,xmm0[10],zero,xmm0[11],zero,xmm0[12],zero,xmm0[13],zero,xmm0[14],zero,xmm0[15],zero
; AVX2-NEXT:    movl $171, %eax
; AVX2-NEXT:    vmovd %eax, %xmm2
; AVX2-NEXT:    vpmullw %ymm2, %ymm1, %ymm1
; AVX2-NEXT:    vpsrlw $8, %ymm1, %ymm1
; AVX2-NEXT:    vextracti128 $1, %ymm1, %xmm2
; AVX2-NEXT:    vpackuswb %xmm2, %xmm1, %xmm1
; AVX2-NEXT:    vpmovzxbw {{.*#+}} ymm1 =
xmm1[0],zero,xmm1[1],zero,xmm1[2],zero,xmm1[3],zero,xmm1[4],zero,xmm1[5],zero,xmm1[6],zero,xmm1[7],zero,xmm1[8],zero,xmm1[9],zero,xmm1[10],zero,xmm1[11],zero,xmm1[12],zero,xmm1[13],zero,xmm1[14],zero,xmm1[15],zero
; AVX2-NEXT:    vpmullw {{.*}}(%rip), %ymm1, %ymm1
; AVX2-NEXT:    vpsrlw $8, %ymm1, %ymm1
; AVX2-NEXT:    vextracti128 $1, %ymm1, %xmm2
; AVX2-NEXT:    vpackuswb %xmm2, %xmm1, %xmm1
; AVX2-NEXT:    vmovdqa {{.*#+}} xmm2 =
[0,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255]
; AVX2-NEXT:    vpblendvb %xmm2, %xmm0, %xmm1, %xmm0
; AVX2-NEXT:    vzeroupper
; AVX2-NEXT:    retq

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