Update and extend context specialization.

Update and extend context specialization.

* Add store-chain folding to context specialization.
* Replace all uses of context with constant and then use
  a visitor to find the places to optimize.

BUG=
R=mstarzinger@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=22993

[Michael Starzinger, 2014-08-08 10:00:17]

LGTM (only nits to address).

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
File src/compiler/js-context-specialization.cc (right):

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.cc:88:
static_cast<Operator1<ContextAccess>*>(node->op())->parameter();
nit: I know this wasn't changed by your CL, but there is a helper for this
casting magic that we could use here instead ...

ContextAccess = OpParameter<ContextAccess>(node);

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.cc:137:
static_cast<Operator1<ContextAccess>*>(node->op())->parameter();
nit: Likewise.

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
File src/compiler/js-context-specialization.h (right):

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.h:18: // some {LoadContext} nodes.
nit: Comment is outdated, let's add "... or strength reducing some
{StoreContext} nodes." here.

https://codereview.chromium.org/440053002/diff/1/test/cctest/compiler/test-js...
File test/cctest/compiler/test-js-context-specialization.cc (right):

https://codereview.chromium.org/440053002/diff/1/test/cctest/compiler/test-js...
test/cctest/compiler/test-js-context-specialization.cc:161: // Immutable slot,
constant context => do nothing.
nit: maybe add "[...], depth = 0 [...]" here.

[sigurds, 2014-08-08 11:00:12]

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
File src/compiler/js-context-specialization.cc (right):

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.cc:88:
static_cast<Operator1<ContextAccess>*>(node->op())->parameter();
On 2014/08/08 10:00:17, Michael Starzinger wrote:
> nit: I know this wasn't changed by your CL, but there is a helper for this
> casting magic that we could use here instead ...
> 
> ContextAccess = OpParameter<ContextAccess>(node);

Done.

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.cc:137:
static_cast<Operator1<ContextAccess>*>(node->op())->parameter();
On 2014/08/08 10:00:17, Michael Starzinger wrote:
> nit: Likewise.

Done.

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
File src/compiler/js-context-specialization.h (right):

https://codereview.chromium.org/440053002/diff/1/src/compiler/js-context-spec...
src/compiler/js-context-specialization.h:18: // some {LoadContext} nodes.
On 2014/08/08 10:00:17, Michael Starzinger wrote:
> nit: Comment is outdated, let's add "... or strength reducing some
> {StoreContext} nodes." here.

Done.

https://codereview.chromium.org/440053002/diff/1/test/cctest/compiler/test-js...
File test/cctest/compiler/test-js-context-specialization.cc (right):

https://codereview.chromium.org/440053002/diff/1/test/cctest/compiler/test-js...
test/cctest/compiler/test-js-context-specialization.cc:161: // Immutable slot,
constant context => do nothing.
On 2014/08/08 10:00:17, Michael Starzinger wrote:
> nit: maybe add "[...], depth = 0 [...]" here.

Done.

[sigurds, 2014-08-08 11:05:38]

Committed patchset #2 manually as 22993 (presubmit successful).