On Fri, Sep 2, 2011 at 7:58 AM, Jiangning Liu <jiangning....@arm.com> wrote:
> Hi,
>
> For the following small case,
>
> int f(int i, int j)
> {
> if (i==1 && j==2)
> return i;
> else
> return j;
> }
>
> with -O2 option, GCC has vrp2 dump like below,
>
> ======================
>
> Value ranges after VRP:
>
> i_1: VARYING
> i_2(D): VARYING
> D.1249_3: [0, +INF]
> j_4(D): VARYING
> D.1250_5: [0, +INF]
> D.1251_6: [0, +INF]
> j_10: [2, 2] EQUIVALENCES: { j_4(D) } (1 elements)
>
>
> Removing basic block 3
> f (int i, int j)
> {
> _Bool D.1251;
> _Bool D.1250;
> _Bool D.1249;
>
> <bb 2>:
> D.1249_3 = i_2(D) == 1;
> D.1250_5 = j_4(D) == 2;
> D.1251_6 = D.1250_5 & D.1249_3;
> if (D.1251_6 != 0)
> goto <bb 3>;
> else
> goto <bb 4>;
>
> <bb 3>:
>
> <bb 4>:
> # i_1 = PHI <1(3), j_4(D)(2)>
> return i_1;
>
> }
>
> ========================
>
> Variable D.1249_3, D.1250_5 and D.1251_6 should be boolean values, so the
> their value ranges should be
>
> D.1249_3: [0, 1]
> D.1250_5: [0, 1]
> D.1251_6: [0, 1]
>
> So why current VRP can't find out this value range?
It does - it just prints it as [0, +INF], they are bools with TYPE_MAX_VALUE
== 1 after all.
Richard.
>
> I'm asking this question because the optimizations in back-end need this
> info to do advanced optimization.
>
> Thanks,
> -Jiangning
>
>
>
