Support double allocations when folding allocation.

Support double allocations when folding allocation.

BUG=
R=mstarzinger@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=15839

[Michael Starzinger, 2013-07-22 19:46:56]

This change does not do what you think it's doing. There is a thinko about
compile-time vs. run-time (see comment in the lithium-codegen-ia32.cc file).

I think a much easier approach would be to make sure the underlying allocation
is aligned at runtime and then just making sure that the offsets used by LEA are
aligned. Thereby you end up with aligned segments and there is no need to adapt
LEA instructions at all.

https://codereview.chromium.org/19956002/diff/5001/src/ia32/lithium-codegen-i...
File src/ia32/lithium-codegen-ia32.cc (right):

https://codereview.chromium.org/19956002/diff/5001/src/ia32/lithium-codegen-i...
src/ia32/lithium-codegen-ia32.cc:4342: __ j(zero, &aligned, Label::kNear);
This is a NOP. The jump at runtime does not affect the modification of offset at
compile time. Also a test+jump seems like overkill.

[Hannes Payer (out of office), 2013-07-22 20:23:13]

This change was ways to complicated, thanks for pointing that out. Handling this
on the higher level is better.

[Michael Starzinger, 2013-07-23 11:24:14]

LGTM with one comment.

https://codereview.chromium.org/19956002/diff/31001/src/hydrogen-instructions.cc
File src/hydrogen-instructions.cc (right):

https://codereview.chromium.org/19956002/diff/31001/src/hydrogen-instructions...
src/hydrogen-instructions.cc:3214: if (!GuaranteedInNewSpace() ||
MustAllocateDoubleAligned() ||
The predicates need to be removed from this early return.

[Hannes Payer (out of office), 2013-07-23 19:26:37]

https://codereview.chromium.org/19956002/diff/31001/src/hydrogen-instructions.cc
File src/hydrogen-instructions.cc (right):

https://codereview.chromium.org/19956002/diff/31001/src/hydrogen-instructions...
src/hydrogen-instructions.cc:3214: if (!GuaranteedInNewSpace() ||
MustAllocateDoubleAligned() ||
On 2013/07/23 11:24:14, Michael Starzinger wrote:
> The predicates need to be removed from this early return.

Done.

[Hannes Payer (out of office), 2013-07-23 19:27:06]

Committed patchset #5 manually as r15839 (presubmit successful).