VM: Use current isolate as immediate in per-isolate stubs.

VM: Use current isolate as immediate operand in per-isolate stub code.

There is no need to load it from the context, if the stub
is per-isolate. This makes those stubs not rely on having a context in CTX,
and avoids loading the isolate pointer from memory.

This CL is part of the effort to free up CTX for general
allocation. Stubs that don't depend on a context in CTX
won't require storing the current context before calling
them.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=40428

[Florian Schneider, 2014-09-17 18:53:52]

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

[srdjan, 2014-09-17 20:41:56]

lgtm

[Florian Schneider, 2014-09-18 10:14:05]

Committed patchset #3 (id:40001) manually as r40428 (presubmit successful).

[Ivan Posva, 2014-09-18 17:31:12]

-Ivan

https://codereview.chromium.org/581703003/diff/40001/runtime/vm/isolate.h
File runtime/vm/isolate.h (right):

https://codereview.chromium.org/581703003/diff/40001/runtime/vm/isolate.h#new...
runtime/vm/isolate.h:117: static inline uword CurrentAddress() {
This is a rather unfortunate name as the function does not return the address of
Current (see Scavenger::TopAddress for an example).

I will rename this to CurrentAsWord() if we need it.

https://codereview.chromium.org/581703003/diff/40001/runtime/vm/stub_code_arm.cc
File runtime/vm/stub_code_arm.cc (right):

https://codereview.chromium.org/581703003/diff/40001/runtime/vm/stub_code_arm...
runtime/vm/stub_code_arm.cc:769: __ LoadImmediate(R8,
Isolate::CurrentAddress());
On second thought I will add a LoadIsolate() to the macro assemblers and remove
CurrentAddress().