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Re: [PATCH] Fix PR37053: Move tweaks of commutative precedence to target hook



I always assumed that one of the main uses of "%" was precisely to allow
regs and mems to be swapped in order to satisfy constraints (which if I've
understood correctly is all that m68k seems to be trying to do).  Declaring
a non-pointer reg + a pointer mem to be noncanonical rtl seems far too strong
at any stage of compilation.  I know 28690 was a serious performance problem,
but I think we need to consider handling this in another way, separating out
"try to achieve this" from "non-canonical".

Also FWIW, this is exactly how I feel. I don't have big problems with Maxim's second patch, but only because '%' is basically unused except for some optimizations within reload. As Maxim taught me (either I remembered wrong or I was really convinced this was not the case), % is not used for matching, so it only really applies whenever two things have the same precedence in the first place.


A third patch could be to extend the usage of '%' but that's probably not a good idea either (what happens if the inverted pair does not satisfy the predicates?) and would require considerably more surgery.

I wonder how much of the performance can be kept on Power6 if you just attack PR28690 within md_reorg. The only problem would be if the index was allocated in r0.

Paolo


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