[turbofan] Use register for instruction operands when SameAsFirst is specified.

[turbofan] Use register for instruction operands when SameAsFirst is specified.

As the register allocator cannot reuse spill slots, SameAsFirst
constraint means that we would have to do an expensive move to a
differen spill slot if we choose to spill. Forcing the operand
to a register is cheaper.

In zlib, we get >10% speed-up for ia32, >25% for x64.

BUG=
R=bmeurer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24580

[Jarin, 2014-10-13 15:14:59]

jarin@chromium.org changed reviewers:
+ bmeurer@chromium.org, mstarzinger@chromium.org

[Jarin, 2014-10-13 15:17:39]

Could you take a look, please?

[Benedikt Meurer, 2014-10-13 18:27:35]

lgtm

[Jarin, 2014-10-14 08:34:29]

Committed patchset #1 (id:1) manually as 24580 (presubmit successful).