Save more memory by compacting LocalVarDescriptors

Save more memory by compacting LocalVarDescriptors

Instead of allocating an array for the names of local variables,
store the names in the LocalVarDescriptors structure directly.

Using dart2js to compile a small dart program results in about 7200
LVDs on the heap.

Retained memory before: 568KB
Retained memory after: 432KB (75%)

R=asiva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=40228

[hausner, 2014-09-12 20:27:57]

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

[siva, 2014-09-12 22:08:39]

LGTM with one suggestion.

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc#newcode...
runtime/vm/object.cc:10801: return raw_ptr()->names()[var_index];
return raw_ptr()->nameAt(var_index);

(see raw_object.h).

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc#newcode...
runtime/vm/object.cc:10809: StorePointer(raw_ptr()->names() + var_index,
name.raw());
StorePointer(&(raw_ptr()->nameAt(var_index)), name.raw());

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h
File runtime/vm/raw_object.h (right):

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h#newc...
runtime/vm/raw_object.h:1108: }
For better readability I think it would make sense to have a method
RawString* nameAt(intptr_t index) const {
  return names()[index];
}

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h#newc...
runtime/vm/raw_object.h:1110: return
reinterpret_cast<RawObject**>(&ptr()->names()[num_entries - 1]);
return reinterpret_cast<RawObject**>(&nameAt(num_enties - 1));

[hausner, 2014-09-12 23:48:04]

PTAL

Added the assertion you suggested offline, and cleaned up usage of raw() and
raw_ptr().

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc#newcode...
runtime/vm/object.cc:10801: return raw_ptr()->names()[var_index];
On 2014/09/12 22:08:39, siva wrote:
> return raw_ptr()->nameAt(var_index);
> 
> (see raw_object.h).

Done.

https://codereview.chromium.org/566053002/diff/1/runtime/vm/object.cc#newcode...
runtime/vm/object.cc:10809: StorePointer(raw_ptr()->names() + var_index,
name.raw());
On 2014/09/12 22:08:39, siva wrote:
> StorePointer(&(raw_ptr()->nameAt(var_index)), name.raw());

Done.

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h
File runtime/vm/raw_object.h (right):

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h#newc...
runtime/vm/raw_object.h:1108: }
On 2014/09/12 22:08:39, siva wrote:
> For better readability I think it would make sense to have a method
> RawString* nameAt(intptr_t index) const {
>   return names()[index];
> }

Added a function to return the address of name[i].

https://codereview.chromium.org/566053002/diff/1/runtime/vm/raw_object.h#newc...
runtime/vm/raw_object.h:1110: return
reinterpret_cast<RawObject**>(&ptr()->names()[num_entries - 1]);
On 2014/09/12 22:08:39, siva wrote:
> return reinterpret_cast<RawObject**>(&nameAt(num_enties - 1));

You can't take the address of a return value.

[siva, 2014-09-12 23:50:48]

lgtm

[hausner, 2014-09-12 23:53:10]

Committed patchset #2 (id:20001) manually as r40228 (presubmit successful).