2012/3/15 Richard Guenther <richard.guent...@gmail.com>: > On Thu, Mar 15, 2012 at 2:09 PM, Kai Tietz <ktiet...@googlemail.com> wrote: >> Hi, >> >> this is the second part of the patch for this problem. It adds some >> basic simplifications for ==/!= >> comparisons for eliminating redudant operands. >> >> It adds the following patterns: >> -X ==/!= Z - X -> Z ==/!= 0. >> ~X ==/!= Z ^ X -> Z ==/!= ~0 >> X ==/!= X - Y -> Y == 0 >> X ==/!= X + Y -> Y == 0 >> X ==/!= X ^ Y -> Y == 0 >> (X - Y) ==/!= (Z - Y) -> X ==/!= Z >> (Y - X) ==/!= (Y - Z) -> X ==/!= Z >> (X + Y) ==/!= (X + Z) -> Y ==/!= Z >> (X + Y) ==/!= (Z + X) -> Y ==/!= Z >> (X ^ Y) ==/!= (Z ^ X) -> Y ==/!= Z > > Can you re-base this patch to work without the previous one? Also > please coordinate with Andrew. Note that all of these(?) simplifications > are already done by fold_comparison which we could share if you'd split > out the EXPR_P op0/op1 cases with separated operands/code. > > Richard.
Hmm, fold_comparison doesn't do the same thing as it checks for possible overflow. This is true for comparisons not being ==/!= or having operands of none-integral-type. But for ==/!= with integral typed arguments the overflow doesn't matter at all. And exactly this is what patch implements here. This optimization of course is just desired in non-AST form, as we otherwise loose information in FE. Therefore I didn't added it to fold_const. I can rework the patch so that it works without the other one. Regards, Kai
