[Bug tree-optimization/85143] New: Loop limit prevents (auto)vectorization

[robertw89 at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85143

            Bug ID: 85143
           Summary: Loop limit prevents (auto)vectorization
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: robertw89 at googlemail dot com
  Target Milestone: ---

I expected that it generates a vectorized version potentially specializing to
the boundary. LLVM produces strange looking (vectorized) code so I guess it's a
but this time :)

Works fine if the hardcoded boundary is removed.

void boxIntersectionSimdNative(
    bool*__restrict__ res,
    double*__restrict__ a, double*__restrict__ b,
    int n
) {
    for( int i = 0; i < n && i < 1337; i++) {
        res[i] = a[i] > b[i];

    }
}


output

boxIntersectionSimdNative(bool*, double*, double*, int):
  test ecx, ecx
  jle .L34
  mov eax, 1
  jmp .L30
.L35:
  cmp r8d, 1336
  jg .L34
.L30:
  vmovsd xmm0, QWORD PTR [rsi-8+rax*8]
  mov r8d, eax
  vcomisd xmm0, QWORD PTR [rdx-8+rax*8]
  seta BYTE PTR [rdi-1+rax]
  add rax, 1
  cmp ecx, r8d
  jg .L35
.L34:
  rep ret