[llvm-bugs] [Bug 47476] New: [SLP] Missed vectorization - division by a constant

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47476

            Bug ID: 47476
           Summary: [SLP] Missed vectorization - division by a constant
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

int a[4], b[4];
void foo()
{
  a[0] = b[0] / 5;
  a[1] = b[1] / 5;
  a[2] = b[2] / 5;
  a[3] = b[3] / 5;
}

Flags:  -O3 -mavx2


Clang:

foo():                                # @foo()
        movsxd  rax, dword ptr [rip + b]
        imul    rax, rax, 1717986919
        mov     rcx, rax
        shr     rcx, 63
        sar     rax, 33
        add     eax, ecx
        mov     dword ptr [rip + a], eax
        movsxd  rax, dword ptr [rip + b+4]
        imul    rax, rax, 1717986919
        mov     rcx, rax
        shr     rcx, 63
        sar     rax, 33
        add     eax, ecx
        mov     dword ptr [rip + a+4], eax
        movsxd  rax, dword ptr [rip + b+8]
        imul    rax, rax, 1717986919
        mov     rcx, rax
        shr     rcx, 63
        sar     rax, 33
        add     eax, ecx
        mov     dword ptr [rip + a+8], eax
        movsxd  rax, dword ptr [rip + b+12]
        imul    rax, rax, 1717986919
        mov     rcx, rax
        shr     rcx, 63
        sar     rax, 33
        add     eax, ecx
        mov     dword ptr [rip + a+12], eax
        ret
a:
        .zero   16

b:
        .zero   16


GCC / ICC:

foo():
        vmovdqu   xmm7, XMMWORD PTR b[rip]                      #4.10
        vmovupd   xmm1, XMMWORD PTR .L_2il0floatpacket.1[rip]   #4.3
        vpsrad    xmm9, xmm7, 31                                #4.3
        vpshufd   xmm0, xmm7, 49                                #4.3
        vpmuldq   xmm2, xmm7, xmm1                              #4.3
        vpmuldq   xmm3, xmm0, xmm1                              #4.3
        vpsrlq    xmm4, xmm2, 32                                #4.3
        vpand     xmm5, xmm3, XMMWORD PTR .L_2il0floatpacket.2[rip] #4.3
        vpor      xmm6, xmm4, xmm5                              #4.3
        vpsrad    xmm8, xmm6, 1                                 #4.3
        vpsubd    xmm10, xmm8, xmm9                             #4.3
        vmovdqu   XMMWORD PTR a[rip], xmm10                     #4.3
        ret

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