[llvm-bugs] [Bug 47889] New: [SLP] Missed vectorization - failed to move load with loop-invariant address

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47889

            Bug ID: 47889
           Summary: [SLP] Missed vectorization - failed to move load with
                    loop-invariant address
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

#define N 16

struct osmesa_context {
  unsigned int clearpixel;
  void *buffer;
};

struct osmesa_context *osmesa;

int run (void *p)
{
  unsigned int i, n, *ptr;

  n = N;

  ptr = (unsigned int *) osmesa->buffer;
  for (i = 0; i < n; i++) {
    *ptr++ = osmesa->clearpixel;
  }

  return 0;
}

ICC and GCC can vectorize this loop.

ICC generates:
run:
  mov rax, QWORD PTR osmesa[rip] #20.26
  mov rdx, QWORD PTR [8+rax] #20.26
  mov rcx, rdx #22.14
  sub rcx, rax #22.14
  cmp rcx, 16 #21.3
  jge ..B1.3 # Prob 50% #21.3
  neg rcx #22.6
  cmp rcx, 64 #21.3
  jl ..B1.4 # Prob 50% #21.3
..B1.3: # Preds ..B1.1 ..B1.2
  movd xmm0, DWORD PTR [rax] #22.14
  pshufd xmm1, xmm0, 0 #22.14
  movdqu XMMWORD PTR [rdx], xmm1 #22.6
  movdqu XMMWORD PTR [16+rdx], xmm1 #22.6
  movdqu XMMWORD PTR [32+rdx], xmm1 #22.6
  movdqu XMMWORD PTR [48+rdx], xmm1 #22.6
  jmp ..B1.5 # Prob 100% #22.6
..B1.4: # Preds ..B1.2
  mov ecx, DWORD PTR [rax] #22.14
  mov DWORD PTR [rdx], ecx #22.6
  mov esi, DWORD PTR [rax] #22.14
  mov DWORD PTR [4+rdx], esi #22.6
  mov edi, DWORD PTR [rax] #22.14
  mov DWORD PTR [8+rdx], edi #22.6
  mov r8d, DWORD PTR [rax] #22.14
  mov DWORD PTR [12+rdx], r8d #22.6
  mov r9d, DWORD PTR [rax] #22.14
  mov DWORD PTR [16+rdx], r9d #22.6
  mov r10d, DWORD PTR [rax] #22.14
  mov DWORD PTR [20+rdx], r10d #22.6
  mov r11d, DWORD PTR [rax] #22.14
  mov DWORD PTR [24+rdx], r11d #22.6
  mov ecx, DWORD PTR [rax] #22.14
  mov DWORD PTR [28+rdx], ecx #22.6
  mov esi, DWORD PTR [rax] #22.14
  mov DWORD PTR [32+rdx], esi #22.6
  mov edi, DWORD PTR [rax] #22.14
  mov DWORD PTR [36+rdx], edi #22.6
  mov r8d, DWORD PTR [rax] #22.14
  mov DWORD PTR [40+rdx], r8d #22.6
  mov r9d, DWORD PTR [rax] #22.14
  mov DWORD PTR [44+rdx], r9d #22.6
  mov r10d, DWORD PTR [rax] #22.14
  mov DWORD PTR [48+rdx], r10d #22.6
  mov r11d, DWORD PTR [rax] #22.14
  mov DWORD PTR [52+rdx], r11d #22.6
  mov ecx, DWORD PTR [rax] #22.14
  mov DWORD PTR [56+rdx], ecx #22.6
  mov eax, DWORD PTR [rax] #22.14
  mov DWORD PTR [60+rdx], eax #22.6
..B1.5: # Preds ..B1.4 ..B1.3
  xor eax, eax #25.10
  ret #25.10


Codegen: https://godbolt.org/z/5f6YnY

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