[Bug tree-optimization/48067] [4.6 Regression] FMA with no add operand produced by convert_mul_to_fma

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48067

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-11 14:50:13 UTC ---
(In reply to comment #2)
> Reproduces on trunk/x86_64 with
> 
>   -O2 -ffast-math -mfma4 -fno-tree-forwprop -fno-tree-reassoc
> 
> on trunk both forwprop and reassoc change
> 
>   d12_8 = -c12_7;
>   D.745_11 = c12_7 - d12_8;
> 
> to
> 
>   D.745_11 = c12_7 + c_12_7;
> 
> making the issue latent.

C testcase with the above flags:

float
foo (float x, float cim)
{
  float c = x * cim;
  float d = -c;
  return c - d;
}