Improve code generation for bounds checks.

Improve code generation for bounds checks.

R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=20872

[Benedikt Meurer, 2014-04-22 08:16:09]

PTAL

[Sven Panne, 2014-04-22 08:25:34]

lgtm

[Benedikt Meurer, 2014-04-22 08:28:27]

Committed patchset #1 manually as r20872 (presubmit successful).

[jbramley, 2014-04-22 08:43:56]

Interesting! I had been looking at this too, but I'd been been distracted by an
interesting corner-case: Sometimes, HBoundsChecks have two constant operands. Is
that intentional? I would have thought that the check would be folded out before
it gets to Lithium, but apparently it doesn't.

[Benedikt Meurer, 2014-04-22 08:45:02]

On 2014/04/22 08:43:56, jbramley wrote:
> Interesting! I had been looking at this too, but I'd been been distracted by
an
> interesting corner-case: Sometimes, HBoundsChecks have two constant operands.
Is
> that intentional? I would have thought that the check would be folded out
before
> it gets to Lithium, but apparently it doesn't.

Yeah, ideally, this should be done at the Hydrogen level, but currently, we
don't get this right in bounds check elimination.