[Bug tree-optimization/48092] associative property of builtins is not exploited on GIMPLE

[rguenther at suse dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48092

--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> 
2011-09-08 10:50:46 UTC ---
On Thu, 8 Sep 2011, vincenzo.innocente at cern dot ch wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48092
> 
> --- Comment #3 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 
> 2011-09-08 10:01:48 UTC ---
> btw even in C  with -Ofast
>  a*exp(x)*exp(y) (same for sqrt) is NOT optimized. compare
> 
> double exp0(double x, double y) {
>    return exp(x)*exp(y);
> }
> 
> double exp1(double a, double x, double y) {
>    return a*exp(x)*exp(y);
> }

Yes, that's because those simplification all are implemented in
fold-const.c.  Compare

double exp03(double a, double x, double y) {
  double tmp1 = exp(x);
  double tmp2 = exp(y);
      return a*(tmp1*tmp2);
}

and in fold-const.c we don't associate FP math.  tree-ssa-reassoc.c
re-associates exp1, but then the simplification is missing - see
my exp03 example.