MIPS: Cleanup handling of shifts: SHR can deoptimize only when its a shift by 0, all other shift ne…

MIPS: Cleanup handling of shifts: SHR can deoptimize only when its a shift by 0, all other shift never deoptimize.

Port r12373 (9fdde2ad)

Original commit message:
Fix DoDeferredNumberTagU to keep the value in xmm1 instead of xmm0 on x64.

xmm0 is not saved across runtime call on x64 because MacroAssembler::EnterExitFrameEpilogue preserves only allocatable XMM registers unlike on ia32 where it preserves all registers.

Cleanup handling of shifts: SHR can deoptimize only when its a shift by 0, all other shift never deoptimize.

Fix type inference for i-to-t change instruction. On X64 this ensures that write-barrier is generated correctly.

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=12831

[palfia, 2012-08-23 23:07:15]

This patch requires the following CL to be landed first:
https://chromiumcodereview.appspot.com/10874047

[palfia, 2012-08-30 22:37:52]

Rebased on r12414

[danno, 2012-10-29 15:08:38]

lgtm