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

[rguenther at suse dot de]

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

--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 8 Jan 2014, hubicka at ucw dot cz wrote:

> 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.

Or simply assign to iftmp.0.  Not sure why iftmp.0 is int
in the first place.  Probably the FEs fault.

Richard.