Ping?
On 10/04/14 06:07, Kugan wrote:
> Value range propagation simplifies convergence in vrp_visit_phi_node by
> setting minimum to TYPE_MIN when the computed minimum is smaller than
> the previous minimum. This can however result in pessimistic value
> ranges in some cases.
>
> for example,
>
> unsigned int i;
> for (i = 0; i < 8; i++)
> {
> ....
> }
>
> # ivtmp_19 = PHI <ivtmp_17(5), 8(2)>
> ...
> <bb 5>:
> ivtmp_17 = ivtmp_19 - 1;
> if (ivtmp_17 != 0)
> ....
> goto <bb 5>;
>
> min value of ivtmp_19 is simplified to 0 (in tree-vrp.c:8465) where as
> it should have been 1. This prevents correct value ranges being
> calculated for ivtmp_17 in the example.
>
> We should be able to see the step (the difference from previous minimum
> to computed minimum) and if there is scope for more iterations (computed
> minimum is greater than step), and then we should be able set minimum to
> do one more iteration and converge to the right minimum value.
>
> Attached patch fixes this. Is this OK for stage-1?
>
> Bootstrapped and regression tested on X86_64-unknown-linux-gnu with no
> new regressions.
>
> Thanks,
> Kugan
>
> gcc/
>
> +2014-04-09 Kugan Vivekanandarajah <kug...@linaro.org>
> +
> + * tree-vrp.c (vrp_visit_phi_node) : Improve value ranges of loop
> + index when simplifying convergence towards minimum.
> +
>
> gcc/testsuite
>
> +2014-04-09 Kugan Vivekanandarajah <kug...@linaro.org>
> +
> + * gcc.dg/tree-ssa/vrp91.c: New test
> +
>
