[Bug tree-optimization/112994] [12/13/14 Regression] Missed optimization for redundancy computation elimination because pattern is broken

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112994

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> It might be a regression but we are still missing a pattern for:
> int n,m;
> void test(int a, int b){
>     m=(a*4)/(a*2);
> }

Yep, and we're seeing that first because when value-numbering

_3 = n.0_2 + b_8;

we're turning that into a_5(D) * 4 via

  x+x -> x*2  (good)
  (x*2)*2 -> x*4  ("bad", doesn't realize the other use of x*2 keeps it live)

we're then missing said pattern.