On 17/11/15 12:10, Bernd Schmidt wrote:
On 11/17/2015 10:08 AM, Kyrill Tkachov wrote:
Yes, I had considered that as well. It should be equivalent. I didn't
use !reg_used_between_p because I thought
it'd be more expensive than checking reg_overlap_mentioned_p since we
must iterate over a number of instructions
and call reg_overlap_mentioned_p on each one. But I suppose this case is
rare enough that it wouldn't make any
measurable difference.
Would you prefer to use !reg_used_between_p here?
I would but apparently it doesn't work, so that's kind of neither here nor
there.
The added comment could lead to some confusion since it's placed in
front of an existing if statement that also tests a different
condition. Also, if we go with your fix,
+ || !reg_overlap_mentioned_p (tmp_reg, SET_SRC (PATTERN
(cand->insn))))
Shouldn't this really be !rtx_equal_p?
Maybe, will it behave the right way if the two regs have different modes
or when subregs are involved?
It would return false, in which case we'll conservatively fail here. I think
that's desirable?
Well, I think the statement we want to make is
"return false from this function if the two expressions contain the same register
number".
if (!rtx_equal_p (..., ...))
return false;
will only return false if the two expressions are the same REG with the same
mode.
if (!reg_overlap_mentioned_p (..., ...))
return false;
should return false even if the modes are different or one is a subreg, which
is what we want.
I did not see any codegen regressions using reg_overlap_mentioned_p on aarch64,
so I don't think
it will restrict any legitimate cases.
Thanks,
Kyrill
Bernd
