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Re: Tiny combine tweek
Jan Hubicka <jh@suse.cz> writes:
>> Wouldn't it be better to notice that the pair of shifts is a noop at
>> the time the IF_THEN_ELSE construct would otherwise be generated?
>
> That code is somewhat generic (what it does is to recursivly walk the
> RTL and try to convert these into if_then_elses - so it first creates if
> then else form of "a", then "a<<1" and so on).
>
> It would be possible to reorder the optimizations so first the normal
> simplification of shifts is done and later we do this trick, but it
> needs more changes too (the combine_simplify_rtx would need to not
> return out of each case of the large switch separately) and doing so
> this way can possibly catch some extra cases where such a noop
> if_then_else is constructed for different reasons...
Okay, in that case I'm willing to approve this patch. Please try to
come up with a test case that can be put into the testsuite; I realize
this is difficult.
zw