Make return statements single steppable

Make return statements single steppable

Replace the code smashing breakpoints at function returns with a call
to a runtime stub that checks whether the debugger is single stepping.
The call to the stub is only emitted in unoptimized code.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31435

[hausner, 2014-01-02 20:30:08]

Happy New Year! :-)

[srdjan, 2014-01-02 21:24:56]

LGTM

https://codereview.chromium.org/106053011/diff/1/runtime/vm/intermediate_lang...
File runtime/vm/intermediate_language.h (right):

https://codereview.chromium.org/106053011/diff/1/runtime/vm/intermediate_lang...
runtime/vm/intermediate_language.h:3431: virtual EffectSet Effects() const {
return EffectSet::None(); }
This may need to be EffectSet::All, as each single step could modify any object.
It does not matter in its currently used context, but is probably right thing to
specify.

[hausner, 2014-01-02 23:32:02]

Committed patchset #2 manually as r31435 (presubmit successful).

[hausner, 2014-01-03 00:43:29]

Done. Also added a Canonicalize method to the new Instruction as discussed
offline to address the performance issues we detected.

https://codereview.chromium.org/106053011/diff/1/runtime/vm/intermediate_lang...
File runtime/vm/intermediate_language.h (right):

https://codereview.chromium.org/106053011/diff/1/runtime/vm/intermediate_lang...
runtime/vm/intermediate_language.h:3431: virtual EffectSet Effects() const {
return EffectSet::None(); }
On 2014/01/02 21:24:56, srdjan wrote:
> This may need to be EffectSet::All, as each single step could modify any
object.
> It does not matter in its currently used context, but is probably right thing
to
> specify.

Done.