[turbofan] Optimize variable loads in DYNAMIC_GLOBAL mode.

[turbofan] Optimize variable loads in DYNAMIC_GLOBAL mode.

This adds a mechanism to the AstGraphBuilder which allows us to build
optimized graphs that respect VariableMode hints for variables bound
to Variable::LOOKUP locations. So far we only use the DYNAMIC_GLOBAL
mode for variable loads.

R=bmeurer@chromium.org

[Michael Starzinger, 2015-05-27 12:08:58]

PTAL. Please be very thorough about style with this CL. Thanks.

[titzer, 2015-05-27 14:06:20]

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

[titzer, 2015-05-27 14:06:22]

https://codereview.chromium.org/1158183002/diff/1/src/compiler/ast-graph-buil...
File src/compiler/ast-graph-builder.cc (right):

https://codereview.chromium.org/1158183002/diff/1/src/compiler/ast-graph-buil...
src/compiler/ast-graph-builder.cc:3233: Node*
AstGraphBuilder::TryVariableLoadDynamicGlobal(
The ordering of the words is kind of mixed up here. Not sure what the best name
is, but I find this one confusing.

[Michael Starzinger, 2015-05-27 14:10:28]

https://codereview.chromium.org/1158183002/diff/1/src/compiler/ast-graph-buil...
File src/compiler/ast-graph-builder.cc (right):

https://codereview.chromium.org/1158183002/diff/1/src/compiler/ast-graph-buil...
src/compiler/ast-graph-builder.cc:3233: Node*
AstGraphBuilder::TryVariableLoadDynamicGlobal(
On 2015/05/27 14:06:21, titzer wrote:
> The ordering of the words is kind of mixed up here. Not sure what the best
name
> is, but I find this one confusing.

Done. True, the name is confusing, changed it to TryDynamicGlobalVariableLoad
which follows the naming convention of the rest of the methods.

[Michael Starzinger, 2015-06-01 17:10:06]

Closing. Superseded by: https://codereview.chromium.org/1150723005/