On 2013/11/12 15:32:10, Weiliang wrote:
On 2013/11/12 10:14:56, Yang wrote:
> On 2013/11/12 09:02:02, Jakob wrote:
> > Nope.
> >
> > var double_one = Math.cos(0);
> >
> > function add(a, b) {
> > return a + b;
> > }
> >
> > assertEquals(1, 1/add(double_one, 0));
> > assertEquals(1, 1/add(0, double_one));
> > %OptimizeFunctionOnNextCall(add);
> > assertEquals(1/(-0 + -0), 1/add(-0, -0));
>
> I suggest adding both tests to minus-zero.js to increase coverage and
prevent
> future mistakes.
Seems the optimization only applys to SMI. so the logic may change to
below
if (representation().IsSmi() || type().IsSmi()) {
result->set_can_be_minus_zero(false);
} else {
result->set_can_be_minus_zero(!to().IsInteger32() ||
!CheckFlag(kAllUsesTruncatingToInt32));
}
Is is reasonable?
There is no fundamental difference between Smi and Integer32 representation
here: both can't explicitly store -0, but might be used for values that
have an
actual value of -0, and must hence check for cases where the difference is
observable.
I'm not sure whether it's possible right now to create a Smi-mode
instruction
where the inputs don't go through a whatever-to-smi change that would deopt
on
inputs that would later create a -0 result, but either way basing further
optimizations on this happenstance would be way too brittle. (And as CL
author
it's your job to convince the reviewer that the change in question can't
possibly go wrong, not the other way round!)
Types are different in that they actually provide some guarantees about
ranges
themselves. However, the current HType system is both inconsistent and
deprecated. I would be highly reluctant to apply any micro-optimizations to
it
at this point -- the next big thing in this area will be consistent use of
the
new "Type" classes we've recently introduced. I think they will
fundamentally
change the whole Range inference system.
https://codereview.chromium.org/61893018/
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