On 8 July 2016 at 12:29, Richard Biener <rguent...@suse.de> wrote:
> On Fri, 8 Jul 2016, Richard Biener wrote:
>
>> 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.
>
> Just verified it works fine on the GCC 5 branch:
>
> Optimizing block #3
>
> 0>>> COPY y_3(D) = x_2(D)
> 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)
> Optimizing statement ret_4 = x_2(D) ^ y_3(D);
> Replaced 'y_3(D)' with variable 'x_2(D)'
> Applying pattern match.pd:240, gimple-match.c:11346
> gimple_simplified to ret_4 = 0;
> Folded to: ret_4 = 0;
I have reported it as PR71947.
Could you help me point out how to fix this ?
Thanks,
Prathamesh
>
> Richard.
