On 07/13/2016 04:15 PM, Richard Biener wrote:
> so not exactly a 50/50 prediction. It is predicted by early return
> predictor it seems. If I make the predictor not apply we predict
> it as 50/50 chance. Hmm. Honza?
Yes, following test-case eliminates the early return predictor:
int foo(int x, int *v)
{
if (x != 0)
x = x / 10;
if (v)
*v += 123;
return x;
}
;; basic block 2, loop depth 0, count 0, freq 10000, maybe hot
;; prev block 0, next block 3, flags: (NEW, REACHABLE)
;; pred: ENTRY [100.0%] (FALLTHRU,EXECUTABLE)
if (x_5(D) != 0)
goto <bb 3>;
else
goto <bb 4>;
;; succ: 3 [50.0%] (TRUE_VALUE,EXECUTABLE)
;; 4 [50.0%] (FALSE_VALUE,EXECUTABLE)
;; basic block 3, loop depth 0, count 0, freq 5000, maybe hot
;; prev block 2, next block 4, flags: (NEW, REACHABLE)
;; pred: 2 [50.0%] (TRUE_VALUE,EXECUTABLE)
x_6 = x_5(D) / 10;
and there's not predictor:
Predictions for bb 2
no prediction heuristics: 50.0%
combined heuristics: 50.0%
Martin
