On Fri, Dec 20, 2013 at 09:26:10AM -0700, Jeff Law wrote:
> >Thanks for working on this, the only thing I'd worry about are
> >HARD_REGNO_NREGS > 1 registers if the two hard regs might overlap.
> The reg_set_between_p and reg_used_between_p calls when you dig down
> into them eventually use reg_overlap_mentioned_p which should do the
> right thing in this regard.
>
> I'll audit ree for problems of this nature.
The two reg_*_between_p functions check only insns in between the two, but
not the insns themselves. What I meant is if it e.g. couldn't be possible
to have HARD_REGNO_NREGS == 2 registers say 1 and 2, where the first insn
would load into the low half of 1, then one insn that say sign extends
1 into {2,3}, then perhaps {2,3} is used and finally 1 is zero extended
into {1,2} and that is used later on. For little endian this would work,
while after the transformation which sign extends the memory into {2,3}
and then copies that into {1,2} (thus overwriting content of low half of
{2,3} with the high half of it). Perhaps the RA will never allow this.
Jakub
