[Bug middle-end/70159] missed CSE optimization

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70159

--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> ---
On Sat, 2 Jul 2016, hiraditya at msn dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70159
> 
> AK <hiraditya at msn dot com> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                  CC|                            |hiraditya at msn dot com
> 
> --- Comment #11 from AK <hiraditya at msn dot com> ---
> Just as an update, the new gvn-hoist pass in llvm hoists the common
> computations:
> 
> @cat test.c
> float foo_p(float d, float min, float max, float a)
> {
>   float tmin;
>   float tmax;
> 
>   float inv = 1.0f / d;
>   if (inv >= 0) {
>     tmin = (min - a) * inv;
>     tmax = (max - a) * inv;
>   } else {
>     tmin = (max - a) * inv;
>     tmax = (min - a) * inv;
>   }
> 
>   return tmax + tmin;
> }
> 
> 
> clang -c -Ofast test.c -mllvm -print-after-all
> 
> 
> *** IR Dump Before Early GVN Hoisting of Expressions ***
> ; Function Attrs: nounwind uwtable
> define float @_Z5foo_pffff(float %d, float %min, float %max, float %a) #0 {
> entry:
>   %div = fdiv fast float 1.000000e+00, %d
>   %cmp = fcmp fast oge float %div, 0.000000e+00
>   br i1 %cmp, label %if.then, label %if.else
> 
> if.then:                                          ; preds = %entry
>   %sub = fsub fast float %min, %a
>   %mul = fmul fast float %sub, %div
>   %sub1 = fsub fast float %max, %a
>   %mul2 = fmul fast float %sub1, %div
>   br label %if.end
> 
> if.else:                                          ; preds = %entry
>   %sub3 = fsub fast float %max, %a
>   %mul4 = fmul fast float %sub3, %div
>   %sub5 = fsub fast float %min, %a
>   %mul6 = fmul fast float %sub5, %div
>   br label %if.end
> 
> if.end:                                           ; preds = %if.else, %if.then
>   %tmax.0 = phi float [ %mul2, %if.then ], [ %mul6, %if.else ]
>   %tmin.0 = phi float [ %mul, %if.then ], [ %mul4, %if.else ]
>   %add = fadd fast float %tmax.0, %tmin.0
>   ret float %add
> }
> 
> 
> *** IR Dump After Early GVN Hoisting of Expressions ***
> ; Function Attrs: nounwind uwtable
> define float @_Z5foo_pffff(float %d, float %min, float %max, float %a) #0 {
> entry:
>   %div = fdiv fast float 1.000000e+00, %d
>   %cmp = fcmp fast oge float %div, 0.000000e+00
>   %sub = fsub fast float %min, %a
>   %mul = fmul fast float %sub, %div
>   %sub1 = fsub fast float %max, %a
>   %mul2 = fmul fast float %sub1, %div
>   br i1 %cmp, label %if.then, label %if.else
> 
> if.then:                                          ; preds = %entry
>   br label %if.end
> 
> if.else:                                          ; preds = %entry
>   br label %if.end
> 
> if.end:                                           ; preds = %if.else, %if.then
>   %tmax.0 = phi float [ %mul2, %if.then ], [ %mul, %if.else ]
>   %tmin.0 = phi float [ %mul, %if.then ], [ %mul2, %if.else ]
>   %add = fadd fast float %tmax.0, %tmin.0
>   ret float %add
> }

Same if you forward-port the patch from PR23286 (just did that).

> cat t.c.126t.pre
...
foo_p (float d, float min, float max, float a)
{
  float inv;
  float tmax;
  float tmin;
  float _16;
  float _18;
  float _19;
  float _20;
  float _21;

  <bb 2>:
  inv_8 = 1.0e+0 / d_7(D);
  _18 = min_9(D) - a_10(D);
  _19 = inv_8 * _18;
  _20 = max_12(D) - a_10(D);
  _21 = inv_8 * _20;
  if (inv_8 >= 0.0)
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:

  <bb 4>:
  # tmin_5 = PHI <_19(2), _21(3)>
  # tmax_6 = PHI <_21(2), _19(3)>
  _16 = tmin_5 + tmax_6;
  return _16;