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 >
