-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 09/29/11 09:26, Bernd Schmidt wrote: > 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. cprop.c -- see references to implicit_sets.
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