[Bug tree-optimization/117821] ~(unsigned smaller type)var_type, the ~ should prop over the truncation (nop too)

[daniel.barboza at oss dot qualcomm.com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117821

Daniel Henrique Barboza <daniel.barboza at oss dot qualcomm.com> changed:

           What    |Removed                     |Added
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                 CC|                            |daniel.barboza at oss dot 
qualcomm
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--- Comment #2 from Daniel Henrique Barboza <daniel.barboza at oss dot 
qualcomm.com> ---
This one is close to 126523 which I have a patch in the ML already so I'll take
a look.

I am assuming that by "the ~ should prop over the truncation" you mean
transforming f2 into f1, i.e. truncate first then do the neg.

It also seems that we can do that not just for bit_ior but also for bit_and and
bit_xor, as long as we guarantee that the immediate has an adequate length for
the trunc operation, e.g. for:

unsigned char f3 (unsigned int a)
{
  a = a (bit_ior|bit_and|bit_xor) 0xFF00FFEE;
  unsigned char t = a;
  return t;
}

This can be turned into:

unsigned char f3 (unsigned int a)
{
  unsigned char t = a;
  t = t (bit_ior|bit_and|bit_xor) 0xEE;
  return t;
}