[turbofan] Optimize silent hole checks on legacy const context slots.

[turbofan] Optimize silent hole checks on legacy const context slots.

Currently we always generate a diamond in the graph builder for every
legacy const context slot, which we cannot get rid of until late control
reduction, even if we know after context specialization that the slot is
already initialized.

Now we generate a select instead, which the CommonOperatorReducer
happily removes during typed lowering. This greatly speeds up asm.js
code generated by Emscripten with the new POINTER_MASKING mode.

R=mstarzinger@chromium.org

Committed: https://crrev.com/35f6c0fdbf7814428d9fdec65cb24c8d4ed17452
Cr-Commit-Position: refs/heads/master@{#27739}

[Benedikt Meurer, 2015-04-10 08:55:53]

Hey Michi,

This is the fix for the hole checks with pointer masking. Please take a look.

Thanks,
Benedikt

[Michael Starzinger, 2015-04-10 09:32:39]

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
File src/compiler/common-operator-reducer.cc (right):

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
src/compiler/common-operator-reducer.cc:115: if (mcond.Is(
We should be able to use the following here ...

Handle<Object> object = HeapObjectMatcher<HeapObject>(cond).Value().handle();
return Replace(object->BooleanValue() ? vtrue : vfalse);

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
src/compiler/common-operator-reducer.cc:197: Factory*
CommonOperatorReducer::factory() const {
If the above suggestion works, then the factory getter here and in the header
file are obsolete.

[Benedikt Meurer, 2015-04-10 09:39:38]

Done, thanks. PTAL

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
File src/compiler/common-operator-reducer.cc (right):

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
src/compiler/common-operator-reducer.cc:115: if (mcond.Is(
On 2015/04/10 09:32:39, Michael Starzinger wrote:
> We should be able to use the following here ...
> 
> Handle<Object> object = HeapObjectMatcher<HeapObject>(cond).Value().handle();
> return Replace(object->BooleanValue() ? vtrue : vfalse);

Done.

https://codereview.chromium.org/1072353002/diff/1/src/compiler/common-operato...
src/compiler/common-operator-reducer.cc:197: Factory*
CommonOperatorReducer::factory() const {
On 2015/04/10 09:32:39, Michael Starzinger wrote:
> If the above suggestion works, then the factory getter here and in the header
> file are obsolete.

Done.

[Michael Starzinger, 2015-04-10 09:56:49]

LGTM.

[Benedikt Meurer, 2015-04-10 10:20:51]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-04-10 10:21:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1072353002/20001

[commit-bot: I haz the power, 2015-04-10 10:28:10]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-10 10:28:27]

Patchset 2 (id:??) landed as
https://crrev.com/35f6c0fdbf7814428d9fdec65cb24c8d4ed17452
Cr-Commit-Position: refs/heads/master@{#27739}