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;
Richard.
