Currently, if the size of two cmp or test operands is a byte or a word, we sign-extend or zero-extend each of them into a 32-bit register before doing the comparison, even when the conditions for the use of a memory operand are met.

This CL makes it possible to load only one of them into a register and address the other as a memory operand.

The tricky bit is that, unlike as in the x64 counterpart http://crrev.com/1780193003, not all registers can be accessed as bytes.

BUG=

Review URL: https://codereview.chromium.org/1845603002

Cr-Commit-Position: refs/heads/master@{#35199}