Optimize one byte string comparisons.

Optimize string length one comparisons by comparing char codes only. Implemented for one byte strings only at the moment. Will add other string types/mixed compares later.

R=fschneider@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31347

[Florian Schneider, 2013-12-20 09:29:12]

LGTM.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1533: new
ConstantInstr(Smi::ZoneHandle(Smi::New(str.CharAt(0))));
Use flow_graph()->GetConstant(Smi::Handle(Smi::New(str.CharAt(0)))) instead.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1584: ConstantInstr* null = new
ConstantInstr(Instance::ZoneHandle());
Use flow_grah()->constant_null().

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1590: ConstantInstr* null = new
ConstantInstr(Instance::ZoneHandle());
Use flow_grah()->constant_null().

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:6809: const intptr_t result = (str.Length()
== 1) ? str.CharAt(0) : -1;
Can the case of Length() > 1 occur at all?

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language.h (right):

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/intermediate_...
runtime/vm/intermediate_language.h:3669: class StringCharCodeInstr : public
TemplateDefinition<1> {
Why packing two different instructions into one? I'd rather have ToCharCode and
FromCharCode as separate instructions. They don't seem to share much code
anyway.

[srdjan, 2013-12-20 19:48:02]

Thanks.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1533: new
ConstantInstr(Smi::ZoneHandle(Smi::New(str.CharAt(0))));
On 2013/12/20 09:29:12, Florian Schneider wrote:
> Use flow_graph()->GetConstant(Smi::Handle(Smi::New(str.CharAt(0)))) instead.


Done, and using ZoneHandle since the handle escapes this scope. Also removed
InsertBefore below, as I do not need to add constants in the list, and it does
not work for shared constant instructions.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1584: ConstantInstr* null = new
ConstantInstr(Instance::ZoneHandle());
On 2013/12/20 09:29:12, Florian Schneider wrote:
> Use flow_grah()->constant_null().

Done.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:1590: ConstantInstr* null = new
ConstantInstr(Instance::ZoneHandle());
On 2013/12/20 09:29:12, Florian Schneider wrote:
> Use flow_grah()->constant_null().

Done.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/flow_graph_op...
runtime/vm/flow_graph_optimizer.cc:6809: const intptr_t result = (str.Length()
== 1) ? str.CharAt(0) : -1;
On 2013/12/20 09:29:12, Florian Schneider wrote:
> Can the case of Length() > 1 occur at all?

Yes, length 0 as well. StringToCharCode has as its input any string and returns
-1 if the string is not of length one, thus it will not match/equal to a string
of length 1.

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language.h (right):

https://codereview.chromium.org/105143011/diff/40001/runtime/vm/intermediate_...
runtime/vm/intermediate_language.h:3669: class StringCharCodeInstr : public
TemplateDefinition<1> {
On 2013/12/20 09:29:12, Florian Schneider wrote:
> Why packing two different instructions into one? I'd rather have ToCharCode
and
> FromCharCode as separate instructions. They don't seem to share much code
> anyway.

Split it up in two instructions.

[srdjan, 2013-12-20 20:11:46]

Committed patchset #5 manually as r31347 (presubmit successful).