Add flag --support_debugger, controls emitting single stepping checks. Disable in --noopt, 6% gain.

Add flag --support_debugger, controls emitting single stepping checks. Disable in --noopt,  6% gain.

R=fschneider@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45641

[srdjan, 2015-05-05 15:17:44]

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

[hausner, 2015-05-05 15:59:15]

hausner@google.com changed reviewers:
+ hausner@google.com

[hausner, 2015-05-05 15:59:15]

DBC

https://codereview.chromium.org/1127523004/diff/1/runtime/vm/flow_graph_build...
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/1127523004/diff/1/runtime/vm/flow_graph_build...
runtime/vm/flow_graph_builder.cc:38: DEFINE_FLAG(bool, support_debugger, true,
"Emit code needed for debugging");
Would be nice to use the --debug command line option for this, but unfortunately
that lives in the embedder. Maybe you can at least programmatically set this
flag when --debug is used? Otherwise we force users to remember and type several
flags when they want to debug a program.

[Florian Schneider, 2015-05-05 16:16:05]

The single-step checks in the stub code should also be controlled by this flag.
This would give even better performance with --noopt.

[srdjan, 2015-05-06 21:02:48]

On 2015/05/05 16:16:05, Florian Schneider wrote:
> The single-step checks in the stub code should also be controlled by this
flag.
> This would give even better performance with --noopt.

Yes, will do that. Will ping you when I am ready with additional changes

[srdjan, 2015-05-06 21:02:54]

https://codereview.chromium.org/1127523004/diff/1/runtime/vm/flow_graph_build...
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/1127523004/diff/1/runtime/vm/flow_graph_build...
runtime/vm/flow_graph_builder.cc:38: DEFINE_FLAG(bool, support_debugger, true,
"Emit code needed for debugging");
On 2015/05/05 15:59:15, hausner wrote:
> Would be nice to use the --debug command line option for this, but
unfortunately
> that lives in the embedder. Maybe you can at least programmatically set this
> flag when --debug is used? Otherwise we force users to remember and type
several
> flags when they want to debug a program.

This flag should not be used by user, the flag will be set only when running
with --noopt, for precompilation, when no debugging is supported. Right now we
can also use it internally for measuring overheade by debugging code.

[srdjan, 2015-05-08 08:50:19]

PTAL

[Florian Schneider, 2015-05-08 10:05:09]

lgtm

[srdjan, 2015-05-08 10:33:31]

Committed patchset #5 (id:70001) manually as r45641 (presubmit successful).