[Bug tree-optimization/59660] We fail to optimize common boolean checks pre-inlining

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59660

--- Comment #6 from Jan Hubicka <hubicka at ucw dot cz> ---
> That's only optimizable after the 'mergephi' pass.  Before the
> temporary setting is shared by the n==m code.  Thus maybe
> 'mergephi' itself can handle this ...

Yep, mergephi seems like resonable place (at least it shares a lot of
letters in the pass name as phiopt).

I still think gimplifier itself could produce instead of:

m_is_less_than_n (int n, int m)
{
  _Bool D.2089;
  int D.2088;
  int iftmp.0;
  _Bool D.2082;

  if (n == m) goto <D.2084>; else goto <D.2087>;
  <D.2087>:
  D.2088 = n + -1;
  D.2089 = m_is_less_than_n (D.2088, m);
  if (D.2089 != 0) goto <D.2084>; else goto <D.2085>;
  <D.2084>:
  iftmp.0 = 1;
  goto <D.2086>;
  <D.2085>:
  iftmp.0 = 0;
  <D.2086>:
  D.2082 = (_Bool) iftmp.0;
  goto <D.2090>;
  <D.2090>:
  return D.2082;
}

simplified version

m_is_less_than_n (int n, int m)
{
  _Bool D.2089;
  int D.2088;
  int iftmp.0;
  _Bool D.2082;

  if (n == m) goto <D.2084>; else goto <D.2087>;
  <D.2084>
  D.2082 = 0;
  goto D.2090
  <D.2087>:
  D.2088 = n + -1;
  D.2082 = m_is_less_than_n (D.2088, m);
  goto <D.2090>;
  <D.2090>:
  return D.2082;
}

Since this is pretty common pattern it should show as compile time improvement
even at -O0.

Honza