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. Regards, Kai
