2011/5/19 Richard Guenther <richard.guent...@gmail.com>: > On Thu, May 19, 2011 at 3:08 PM, Kai Tietz <ktiet...@googlemail.com> wrote: >> 2011/5/19 Richard Guenther <richard.guent...@gmail.com>: >>> On Thu, May 19, 2011 at 2:59 PM, Kai Tietz <ktiet...@googlemail.com> wrote: >>>> 2011/5/19 Richard Guenther <richard.guent...@gmail.com>: >>>>> On Thu, May 19, 2011 at 2:48 PM, Kai Tietz <ktiet...@googlemail.com> >>>>> wrote: >>>>>> Hello, >>>>>> >>>>>> This patch improves reassociation folding for comparision. It expands >>>>>> expressions within binary-AND/OR expression like (X | Y) == 0 to (X == >>>>>> 0 && Y == 0) >>>>>> and (X | Y) != 0 to (X != 0 || Y != 0). This is necessary to allow >>>>>> better reassociation >>>>>> on weak pre-folded logical expressions. This unfolding gets undone >>>>>> anyway later by pass, >>>>>> so no disadvantage gets introduced. >>>>>> Also while going through BB-list, it tries to do some little >>>>>> type-sinking for SSA sequences >>>>>> like "D1 = (type) bool1; D2 = (type) bool2; D3 = D1 & D2;' to 'D1 = >>>>>> bool1 & bool2; D2 = (type) D1;'. >>>>>> This folding has the advantage to see better through intermediate >>>>>> results with none-boolean type. >>>>>> The function eliminate_redundant_comparison () got reworded so, that >>>>>> doesn't break in all cases. >>>>>> It now continues to find duplicates and tries to find inverse variant >>>>>> (folded to constant). By this >>>>>> change we don't combine possible weak optimizations too fast, before >>>>>> we can find and handle >>>>>> inverse or duplicates. >>>>> >>>>> sinking casting belongs not here but instead to tree-ssa-forwprop. >>>>> I'm not sure that a != 0 | b != 0 is the better canonical variant than >>>>> a | b != 0 though. >>>>> >>>>> is_boolean_compatible_type_p looks like a strange remanent. >>>>> >>>>> Richard. >>>> >>>> Well, a | b != 0 is for sure more optimal, but for reassociation we >>>> need to see the unfolded variant temporary. This is necessary as >>>> fold-const can't see through SSA statements. But this kind of >>>> expansion should be reversed then by pass to the form (a | b) != 0 >>>> back. >>> >>> ? fold-const shouldn't deal with this at all as we are in gimple and in >>> SSA form. Surely re-association comes to play only with chains of >>> the above with more than two operands. >>> >>> Richard. >>> >>>> >>>> Regards, >>>> Kai >>>> >>> >> >> The issue you can see by testcase binop_tor4.c, as here are the >> intermediate variables d and e (with int type) are destroying the >> reassociation pass. This testcase for example needs this sinking. > > hoisting would work equally well
Well, but just if then all operands in combined BIT_AND/OR block are getting hoisting. And well, there might be still some cases where we wouldn't find the equivalent. As hoisting leads to following sequences, eg: D1 = a != 0; D2 = b != 0; D3 = a == 0; D4 = b == 0; D5 = (long) D1 D6 = (long) D2 D7 = (long) D3 D8 = (long) D4 D9 = D5 & D6; D10 = D8 & D9 D11 = D9 & D10; which means that comparision folding will never will happen as the statement passed to fold algorithm is a cast to a comparison and not the comparison itself. So sinking looks more sane IMHO. Regards, Kai
