Eli, Could you have a look at ChooseConstraint in LLVM and confirm whether or not it is choosing multiple alternative constraints? It seems to me that the backend is in a better position to choose them. Having studied ChooseConstraintTuple, I was in the process of trying something similar in the front end, when my boss suggested that the back end was a better place, leading me to have a look inside LLVM. It looks like there is some basic support for it, though not all constraint types are supported. I even saw a comment somewhere about "|" being used in the constrainst, though I didn't see any support for it, but it suggested to me that it might have been considered as a means for separating the alternative constraints. One thing I also noticed is that the back-end doesn't consider multiple constraints in parallel, as ChooseConstraintTuple does, but it seems like it should be okay, as long as the backend can find suitable instrustions.
-John On Thu, Aug 5, 2010 at 6:08 PM, Eli Friedman <[email protected]> wrote: > On Thu, Aug 5, 2010 at 5:40 PM, John Thompson > <[email protected]> wrote: > > May I check this in? > > No, it's wrong; the correct approach is > http://llvm.org/bugs/show_bug.cgi?id=7338#c6 . I think you're not > understanding the part of multi-alternative constraints that requires > only one alternative to be selected. > > -Eli > -- John Thompson [email protected]
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