VM: Better type propagation for string objects.

VM: Better type propagation for string objects.

For strings we can't propagate the class-id because of externalization,
but we still can record the compile-type (String). This is for example useful
for eliminating number-checks with identical-comparisons.

R=vegorov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=44133

[Florian Schneider, 2015-03-02 10:46:28]

fschneider@google.com changed reviewers:
+ vegorov@google.com

[Vyacheslav Egorov (Google), 2015-03-02 12:52:53]

LGTM with MaybeNumber fixed.

Condition in MaybeNumber in intermediate_language.cc needs to take Object into
account. We arrived to the repro, please add it as well.

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
File runtime/vm/flow_graph_type_propagator.cc (right):

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:185: if (cid == kOneByteStringCid ||
cid == kTwoByteStringCid) {
(cid == ...) || (cid == ...)

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:293: // TODO(vegorov): If check is
affected by side-effect we can still propagate
You can add similar code here :)

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:305: // TODO(vegorov): If check is
affected by side-effect we can still propagate
You can add similar code here :)

[Florian Schneider, 2015-03-02 13:16:13]

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
File runtime/vm/flow_graph_type_propagator.cc (right):

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:185: if (cid == kOneByteStringCid ||
cid == kTwoByteStringCid) {
On 2015/03/02 12:52:53, Vyacheslav Egorov (Google) wrote:
> (cid == ...) || (cid == ...)

Done.

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:293: // TODO(vegorov): If check is
affected by side-effect we can still propagate
On 2015/03/02 12:52:52, Vyacheslav Egorov (Google) wrote:
> You can add similar code here :)

Acknowledged.

https://codereview.chromium.org/966773002/diff/1/runtime/vm/flow_graph_type_p...
runtime/vm/flow_graph_type_propagator.cc:305: // TODO(vegorov): If check is
affected by side-effect we can still propagate
On 2015/03/02 12:52:52, Vyacheslav Egorov (Google) wrote:
> You can add similar code here :)

Acknowledged.

[Florian Schneider, 2015-03-02 16:10:36]

Committed patchset #2 (id:20001) manually as r44133 (presubmit successful).