[Bug tree-optimization/123385] New: GCC failed loop strength reduction for vectorized IV

[liuhongt at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123385

            Bug ID: 123385
           Summary: GCC failed loop strength reduction for vectorized IV
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: liuhongt at gcc dot gnu.org
  Target Milestone: ---

__attribute__((aligned(64) )) float a[10000];

int foo()
{
    for (int i = 0; i < 10000; i++)
    {
        a[i] = (float)(i * 10);
    }
    return 0;
}

After vectorization:

  <bb 3> [local count: 1063004408]:
  # vect_vec_iv_.4_9 = PHI <_8(5), { 0, 1, 2, 3 }(2)>
  # ivtmp.12_4 = PHI <ivtmp.12_10(5), ivtmp.12_1(2)>
  vect__1.5_13 = vect_vec_iv_.4_9 * { 10, 10, 10, 10 };  
  vect__2.6_14 = (vector(4) float) vect__1.5_13;
  # DEBUG i => NULL
  # DEBUG BEGIN_STMT
  _2 = (void *) ivtmp.12_4;
  MEM <vector(4) float> [(float *)_2] = vect__2.6_14;
  # DEBUG BEGIN_STMT
  # DEBUG i => NULL
  # DEBUG BEGIN_STMT
  _8 = vect_vec_iv_.4_9 + { 4, 4, 4, 4 };
  ivtmp.12_10 = ivtmp.12_4 + 16;
  if (ivtmp.12_10 != _3)
    goto <bb 5>; [98.99%]
  else
    goto <bb 4>; [1.01%]

  <bb 5> [local count: 1052266995]:
  goto <bb 3>; [100.00%]



This:
  # vect_vec_iv_.4_9 = PHI <_8(5), { 0, 1, 2, 3 }(2)>
  vect__1.5_13 = vect_vec_iv_.4_9 * { 10, 10, 10, 10 };
  ...
  _8 = vect_vec_iv_.4_9 + { 4, 4, 4, 4 };

Can be folded into

  <bb 3> [local count: 1063004408]:
  # vect_vec_iv_.4_9 = PHI <_8(5), { 0, 10, 20, 30 }(2)>
  vect__1.5_13 = vect_vec_iv_.4_9
  ...
  _8 = vect_vec_iv_.4_9 + { 40, 40, 40, 40 };