[Bug tree-optimization/96685] Failure to optimize not+sub to add+not

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96685

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Though, there is some canonicalization problem GENERIC vs. GIMPLE:
unsigned
f1 (unsigned x, unsigned y)
{
  unsigned int r = (x - y);
  return ~r;
}

unsigned
f2 (unsigned x, unsigned y)
{
  unsigned int r = ~(x - y);
  return r;
}

unsigned
f3 (unsigned x)
{
  unsigned int r = (x - 23);
  return ~r;
}

unsigned
f4 (unsigned x)
{
  unsigned int r = ~(x - 23);
  return r;
}

int
f5 (int x, int y)
{
  int r = (x - y);
  return ~r;
}

int
f6 (int x, int y)
{
  int r = ~(x - y);
  return r;
}

int
f7 (int x)
{
  int r = (x - 23);
  return ~r;
}

int
f8 (int x)
{
  int r = ~(x - 23);
  return r;
}

Before the above patch, the above testcase emitted:
        subl    %esi, %edi
        movl    %edi, %eax
        notl    %eax
for f1/f2/f5/f6 and
        leal    -23(%rdi), %eax
        notl    %eax
for f3/f4/f7/f8.
With the patch it emits:
        notl    %edi
        leal    (%rdi,%rsi), %eax
for f1/f5/f6,
        subl    %edi, %esi
        leal    -1(%rsi), %eax
for f2,
        notl    %edi
        leal    23(%rdi), %eax
for f3/f7,
        movl    $22, %eax
        subl    %edi, %eax
for f4/f8.