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>

Review URL: https://codereview.chromium.org/19248002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15782 ce2b1a6d-e550-0410-aec6-3dcde31c8c00