On 09/29/11 16:43, Rahul Kharche wrote: > >> insn 882 : cc <- compare (r684, 0) >> jump_insn 883 : if (cc != 0) goto insn 46 >> insn 49 : r291 <- r684 >> ...... >> insn 46 >> >> cc contains the result of subtracting 0 from r684; control flow goes to >> insn_49 only if (cc == 0), which implies (r684 == 0). >> Then at insn_49 we have conditional const propagation "r684 <- 0", is it >> right? >> > > I believe, the optimization you may be referring to is value range > propagation which does predication of values based on predicates of > conditions. GCC definitely applies VRP at the tree stage, I am not > sure if there is an RTL pass to do the same.
ISTR cse.c has some support for this. Bernd
