[turbofan] Eliminate redundant masking operations for word8/word16 stores.

[turbofan] Eliminate redundant masking operations for word8/word16 stores.

There's no need to apply 0xff when storing 8-bit values or 0xffff when
storing 16-bit values.

TEST=unittests
R=titzer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=24492

[Benedikt Meurer, 2014-10-09 10:51:28]

bmeurer@chromium.org changed reviewers:
+ titzer@chromium.org

[Benedikt Meurer, 2014-10-09 10:51:28]

PTAL

[titzer, 2014-10-09 10:54:47]

https://codereview.chromium.org/642033002/diff/1/src/compiler/machine-operato...
File src/compiler/machine-operator-reducer.cc (right):

https://codereview.chromium.org/642033002/diff/1/src/compiler/machine-operato...
src/compiler/machine-operator-reducer.cc:484: (rep == kRepWord16 &&
(m.right().Value() & 0xffff) == 0xffff))) {
We could generalize this to 64-bits as well, but probably not worth it. Can you
drop a TODO(turbofan) here?

[titzer, 2014-10-09 10:55:19]

lgtm

[Benedikt Meurer, 2014-10-09 12:20:57]

Committed patchset #2 (id:20001) manually as 24492 (presubmit successful).