Bug fix in load elimination, constant propagation for LoadClassId.

Bug fix in load elimination,  constant propagation for LoadClassId.

Handle LoadClassId in constant propagation. This helps with eliminating
unreachable code after polymorphic inlining. It exposed a bug which is
also fixed in this CL.

Redefinitions of values have to be considered for load/store forwarding:
Loads/stores to an object defined by a RedefinitionInstr (inserted by
polymorphic inlining) must be treated properly as loads/stores to the
original object.

R=kmillikin@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28159

[Kevin Millikin (Google), 2013-10-02 12:36:19]

LGTM.

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:4305: static Definition* Unwrap(Definition*
defn) {
Even though it's only used locally, this name is too generic.  Try something
snazzy like OriginalDefinitionOf or RealDefinitionOf.

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:6295: SetValue(instr, non_constant_);
You could also try this: if instr->object() has a constant value that is an
instance (I guess it should be), then set this instruction's constant value to
that one's class ID.

[Florian Schneider, 2013-10-02 12:58:41]

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:4305: static Definition* Unwrap(Definition*
defn) {
On 2013/10/02 12:36:19, kmillikin wrote:
> Even though it's only used locally, this name is too generic.  Try something
> snazzy like OriginalDefinitionOf or RealDefinitionOf.

Done.

https://codereview.chromium.org/25640004/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:6295: SetValue(instr, non_constant_);
On 2013/10/02 12:36:19, kmillikin wrote:
> You could also try this: if instr->object() has a constant value that is an
> instance (I guess it should be), then set this instruction's constant value to
> that one's class ID.

Done.

[Florian Schneider, 2013-10-02 13:30:17]

Committed patchset #3 manually as r28159 (presubmit successful).