Is VRP is too conservative to identify boolean value 0 and 1?

[Jiangning Liu]

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?

I'm asking this question because the optimizations in back-end need this
info to do advanced optimization.

Thanks,
-Jiangning