Add HLoadRoot hydrogen instruction.

Add HLoadRoot hydrogen instruction.

R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16807

[Benedikt Meurer, 2013-09-17 09:35:02]

Hey danno,
Here's the new HLoadRoot instruction which is required for the
NumberToStringStub hydrogen version. It simply translates to the LoadRoot macro
assembler instruction.
It's using kDependsOnCalls as suggested by mstarzinger@ because we cannot add
anymore GVN flags right now w/o going to int64_t for the flags field, and we
don't need the kDependsOnRoots until we actually add the HStoreRoot instruction.
PTAL
-- Benedikt

[Sven Panne, 2013-09-19 06:06:19]

lgtm

[Benedikt Meurer, 2013-09-19 06:08:26]

Committed patchset #1 manually as r16807 (presubmit successful).

[titzer, 2013-09-19 16:33:47]

On 2013/09/19 06:08:26, Benedikt Meurer wrote:
> Committed patchset #1 manually as r16807 (presubmit successful).

I don't like the idea of another instruction modeling a direct load. We already
have 3 types of loads as it is: HLoadNamedField, HLoadKeyed, and
HLoadGlobalCell. I think at least one of them should be capable of modeling a
load from the root set.

[Benedikt Meurer, 2013-09-20 05:32:45]

On 2013/09/19 16:33:47, titzer wrote:
> On 2013/09/19 06:08:26, Benedikt Meurer wrote:
> > Committed patchset #1 manually as r16807 (presubmit successful).
> 
> I don't like the idea of another instruction modeling a direct load. We
already
> have 3 types of loads as it is: HLoadNamedField, HLoadKeyed, and
> HLoadGlobalCell. I think at least one of them should be capable of modeling a
> load from the root set.

I was talking to danno about this, but the other instructions are already way
too complex, and danno recommended to add a new one instead.