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Re: dangerous cleverness? ppc int<->float conversions, subreg


>>>>> Dale Johannesen writes:

Dale> We've noticed this on Darwin too.  I'm not sure anybody's mentioned
Dale> this point:  the alignment requirements for "double" memrefs can be
Dale> more restrictive than those for (non-double-containing) structs.  A
Dale> misaligned FP load/store may be much slower than two int load/stores,
Dale> or may fail completely.  I don't think there's anyplace in the code
Dale> that's checking this.

	See SLOW_UNALIGNED_ACCESS macro in rs6000.h.  It is checking.
There may be something wrong with the alignment it calculates.

	FPR use for moves decreased after this change.  This is why I know
that FPR use can be prevented completely with the right cost model in the
move_by_pieces tuning.  The important point is don't assume that one
*always* wants to avoid FPRs for DImode moves, in other words don't
hard-code a high cost. 

David


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