Fix unaligned accesses in back_edge tables.

Fix unaligned accesses in back_edge tables.

This patch fixes the step size of masm->pc_ in back_edge tables to words (4 bytes) to ensure 4 bytes alignment for read/write operations. Read and write of words (4 bytes) data from aligned space (address % 4 == 0) is more efficient on all platforms and especially on MIPS where without this alignment fix a kernel exception handler is used for every unaligned access.

This patch increases the size of back_edge tables by 3 bytes in every row. By the test it seem the back_edge table quite small in every/most cases (maximal length is 18 so in that case there are only 54 additional bytes with this patch).

BUG=

Patch from Douglas Leung <Douglas.Leung@imgtec.com>;

[kisg, 2013-07-18 15:46:52]

https://codereview.chromium.org/19248002/diff/1/src/deoptimizer.cc
File src/deoptimizer.cc (right):

https://codereview.chromium.org/19248002/diff/1/src/deoptimizer.cc#newcode2434
src/deoptimizer.cc:2434: int32_t loop_depth = Memory::int32_at(back_edge_cursor
+ 2 * kIntSize);
Instead of int32_t, use uint32_t and static_cast<int> in the CHECK to fix debug
builds

[kisg, 2013-07-18 18:12:03]

LGTM

[kilvadyb, 2013-07-18 18:22:43]

https://codereview.chromium.org/19248002/diff/1/src/deoptimizer.cc
File src/deoptimizer.cc (right):

https://codereview.chromium.org/19248002/diff/1/src/deoptimizer.cc#newcode2434
src/deoptimizer.cc:2434: int32_t loop_depth = Memory::int32_at(back_edge_cursor
+ 2 * kIntSize);
On 2013/07/18 15:46:52, kisg wrote:
> Instead of int32_t, use uint32_t and static_cast<int> in the CHECK to fix
debug
> builds

Done.

[Jakob Kummerow, 2013-07-19 12:58:44]

lgtm

[palfia, 2013-07-19 14:47:19]

Committed as r15782.