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Re: missing conditional propagation in cprop.c pass

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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.

jeff
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