[Bug tree-optimization/71842] New: Optimize FMA when some arguments are simple constants

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71842

            Bug ID: 71842
           Summary: Optimize FMA when some arguments are simple constants
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
  Target Milestone: ---

#include <math.h>
double f(double x, double y){ return fma(x, y, 0.); }
double g(double x, double y){ return fma(0., x, y); }
double h(double x){ return fma(3., 4., x); }

Depending on compiler options, we could optimize those to x*y, y and 12.+x.
fma(1,x,y) might also be x+y.