2011/7/8 Richard Guenther <richard.guent...@gmail.com>: > On Thu, Jul 7, 2011 at 6:28 PM, Kai Tietz <ktiet...@googlemail.com> wrote: >> 2011/7/7 Paolo Bonzini <bonz...@gnu.org>: >>> On 07/07/2011 06:07 PM, Kai Tietz wrote: >>>> >>>> + /* We redo folding here one time for allowing to inspect more >>>> + complex reductions. */ >>>> + substitute_and_fold (op_with_constant_singleton_value_range, >>>> + vrp_fold_stmt, false); >>>> + /* We need to mark this second pass to avoid re-entering of same >>>> + edges for switch statments. */ >>>> + in_second_pass = true; >>>> substitute_and_fold (op_with_constant_singleton_value_range, >>>> vrp_fold_stmt, false); >>>> + in_second_pass = false; >>> >>> This needs a much better explanation. >>> >>> Paolo >> >> Well, I can work on a better comment. The complex reduction I mean >> here are cases like >> >> int x; >> int y; >> _Bool D1; >> _Bool D2; >> _Bool D3; >> int R; >> >> D1 = x[0..1] != 0; >> D2 = y[0..1] != 0; >> D3 = D1 & D2 >> R = (int) D3 >> >> (testcase is already present. See tree-ssa/vrp47.c). >> >> As VRP in first pass produces (and replaces) to: >> >> D1 = (_Bool) x[0..1]; >> D2 = (_Bool) y[0..1]; >> D3 = D1 & D2 >> R = (int) D3 >> >> Just in the second pass the reduction >> >> R = x[0..1] & y[0..1] > > So why wouldn't that happen during the first pass? The first > pass could change the IL to > > D1 = x[0..1] != 0; > D2 = y[0..1] != 0; > D3 = D1 & D2; > R = x & y; > > if D3 only has a single use. > >> can happen. In general it is sad that VRP can't insert during pass >> new statements right now. This would cause issues in range-tables, >> which aren't designed for insertations. As otherwise, we could do >> also simplify things like >> >> D1 = x[0..1] != 0; >> D2 = y[0..1] == 0; >> D3 = D1 & D2 >> R = (int) D3 >> >> to >> R = x[0..1] & (y[0..1] ^ 1) > > Why that ^ 1? And why does that confuse the range tables > if you re-use R?
Because (y[0..1] ^1) has a type change. All present SSA-nodes have boolean type, but (y[0..1] ^ 1) is an integer one. We have just the cast def, which has final type. See code of vrp_stmt truth and you will notice that for X with range 0..1 it converts X == 0 -> X ^ 1. But here we have possible type change as a comparison is boolean and X might not. Kai >> Regards, >> Kai >> >
