Only assign environments when they are actually needed. (ARM and ARM64 only)

Only assign environments when they are actually needed. (ARM and ARM64 only)

Twin of https://codereview.chromium.org/210783003/ and https://codereview.chromium.org/211153003/.

Cleaned up DoChange a bit on the way, making things more uniform across platforms, removed useless comments etc.

R=yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=20376

[Sven Panne, 2014-03-31 12:18:06]

Added ARM64, too, plus some minor unification of things in DoChange. PTAL...

[Yang, 2014-04-01 06:56:01]

lgtm.

https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc
File src/arm/lithium-arm.cc (right):

https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc#n...
src/arm/lithium-arm.cc:1917: LOperand* value = UseRegisterAtStart(val);
Is moving this line into each one of the three if/else-block intended?

[Sven Panne, 2014-04-01 07:05:56]

https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc
File src/arm/lithium-arm.cc (right):

https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc#n...
src/arm/lithium-arm.cc:1917: LOperand* value = UseRegisterAtStart(val);
On 2014/04/01 06:56:01, Yang wrote:
> Is moving this line into each one of the three if/else-block intended?

Yes, I find this much more readable when the register constraints are close
together. It is just by accident that "value" has the same constraint in all
three branches. Therefore lifting it out seems to give it some meaning that it
doesn't really have. Imagine if e.g. LNumberTagI needed some other constraint:
Then you would have to do this refactoring, anyway.

Put another way: Combining totally random stuff to save 2 lines is bad... :-)

[Yang, 2014-04-01 07:06:49]

On 2014/04/01 07:05:56, Sven Panne wrote:
> https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc
> File src/arm/lithium-arm.cc (right):
> 
>
https://codereview.chromium.org/214613004/diff/20001/src/arm/lithium-arm.cc#n...
> src/arm/lithium-arm.cc:1917: LOperand* value = UseRegisterAtStart(val);
> On 2014/04/01 06:56:01, Yang wrote:
> > Is moving this line into each one of the three if/else-block intended?
> 
> Yes, I find this much more readable when the register constraints are close
> together. It is just by accident that "value" has the same constraint in all
> three branches. Therefore lifting it out seems to give it some meaning that it
> doesn't really have. Imagine if e.g. LNumberTagI needed some other constraint:
> Then you would have to do this refactoring, anyway.
> 
> Put another way: Combining totally random stuff to save 2 lines is bad... :-)

alright. lgtm.

[Sven Panne, 2014-04-01 07:21:42]

Committed patchset #3 manually as r20376 (presubmit successful).