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Re: subreg against register allocation?
Bernd Schmidt <email@example.com> writes:
> On 06/15/2010 12:06 AM, Ian Lance Taylor wrote:
>> Well, as you know, subregs have two meanings which look similar but
>> are in fact entirely different. It's valid to set subregs of the same
>> pseudo in parallel if the subregs represent different hard registers.
>> It's not valid if the subregs represent different pieces of the same
>> hard register.
> Are you aware of any examples of this in the compiler? The explanation
> is of course plausible, but do we know that we handle this correctly
Hmmm, you could be right. I wrote and tested some examples when
working on lower-subreg, but I never committed them. The current
define_splits in i386.md which can do parallel sets only run if
reload_completed is true, when simplify_gen_subreg will return
different hard registers. While I don't know of any reason that it
wouldn't work, I guess I don't know for sure that it is safe.