Re: [PATCH] Complex move by parts (PR rtl-optimization/20306)

[David Edelsohn <dje at watson dot ibm dot com>]

>>>>> Roger Sayle writes:

Roger> The issue is that different processors have different preferences,
Roger> even for the mem->mem case.  On PowerPC, apparently it's faster to
Roger> block move an array of doubles via FP registers than via integer
Roger> registers, as the peak FPU<->MEM bandwidth is higher than the peak
Roger> CPU<->MEM bandwidth.  Clearly, this isn't the case on IA-32 for
Roger> memory to memory moves, which are most efficiently implemented by
Roger> using integer load/stores and/or IA-32's block move instructions.

	To expand on this further, the current algorithm will set try_int
to true for the many of the complex float cases of interest.

	I can make block_move conditional on try_int and add another test
to the decision tree setting try_int to false for MODE_FLOAT, but the
question is whether this generic cost model is correct for all targets.
Do we still need a target hook to force try_into to false instead of a
generic MODE_FLOAT test?

David