On Fri, 8 Jul 2016, Prathamesh Kulkarni wrote:
> Hi Richard,
> For the following test-case:
>
> int f(int x, int y)
> {
> int ret;
>
> if (x == y)
> ret = x ^ y;
> else
> ret = 1;
>
> return ret;
> }
>
> I was wondering if x ^ y should be folded to 0 since
> it's guarded by condition x == y ?
>
> optimized dump shows:
> f (int x, int y)
> {
> int iftmp.0_1;
> int iftmp.0_4;
>
> <bb 2>:
> if (x_2(D) == y_3(D))
> goto <bb 3>;
> else
> goto <bb 4>;
>
> <bb 3>:
> iftmp.0_4 = x_2(D) ^ y_3(D);
>
> <bb 4>:
> # iftmp.0_1 = PHI <iftmp.0_4(3), 1(2)>
> return iftmp.0_1;
>
> }
>
> The attached patch tries to fold for above case.
> I am checking if op0 and op1 are equal using:
> if (bitmap_intersect_p (vr1->equiv, vr2->equiv)
> && operand_equal_p (vr1->min, vr1->max)
> && operand_equal_p (vr2->min, vr2->max))
> { /* equal /* }
>
> I suppose intersection would check if op0 and op1 have equivalent ranges,
> and added operand_equal_p check to ensure that there is only one
> element within the range. Does that look correct ?
> Bootstrap+test in progress on x86_64-unknown-linux-gnu.
I think VRP is the wrong place to catch this and DOM should have but it
does
Optimizing block #3
1>>> STMT 1 = x_2(D) le_expr y_3(D)
1>>> STMT 1 = x_2(D) ge_expr y_3(D)
1>>> STMT 1 = x_2(D) eq_expr y_3(D)
1>>> STMT 0 = x_2(D) ne_expr y_3(D)
0>>> COPY x_2(D) = y_3(D)
0>>> COPY y_3(D) = x_2(D)
Optimizing statement ret_4 = x_2(D) ^ y_3(D);
Replaced 'x_2(D)' with variable 'y_3(D)'
Replaced 'y_3(D)' with variable 'x_2(D)'
Folded to: ret_4 = x_2(D) ^ y_3(D);
LKUP STMT ret_4 = x_2(D) bit_xor_expr y_3(D)
heh, registering both reqivalencies is obviously not going to help...
The 2nd equivalence is from doing
/* We already recorded that LHS = RHS, with canonicalization,
value chain following, etc.
We also want to record RHS = LHS, but without any
canonicalization
or value chain following. */
if (TREE_CODE (rhs) == SSA_NAME)
const_and_copies->record_const_or_copy_raw (rhs, lhs,
SSA_NAME_VALUE (rhs));
generally recording both is not helpful. Jeff? This seems to be
r233207 (fix for PR65917) which must have regressed this testcase.
Richard.
