Initial support for marking live code.

Initial support for marking live code.

As part of aggressive dead code elimination, we initially assume all
flow-graph instructions are not live.  We mark those that are critical
and recursively all their children.  The children of variable
references (VariableProxies occurring as rvalues) include all their
reaching definitions.

Committed: http://code.google.com/p/v8/source/detail?r=4246

[Kevin Millikin (Chromium), 2010-03-23 13:55:55]

As we discussed, control dependencies are not yet handled.  We need to find a
cheap way to do so.

[fschneider, 2010-03-23 16:14:46]

First round of comments.

http://codereview.chromium.org/1159005/diff/1/2
File src/ast.cc (right):

http://codereview.chromium.org/1159005/diff/1/2#newcode647
src/ast.cc:647: return expression()->IsPrimitive();
This should be 

return !expression()->IsPrimitive();

right?

http://codereview.chromium.org/1159005/diff/1/3
File src/ast.h (right):

http://codereview.chromium.org/1159005/diff/1/3#newcode292
src/ast.h:292: int is_live() const { return LiveField::decode(bitfields_); }
This should return a bool.

http://codereview.chromium.org/1159005/diff/1/5
File src/data-flow.cc (right):

http://codereview.chromium.org/1159005/diff/1/5#newcode2082
src/data-flow.cc:2082: List<AstNode*> stack;
Maybe set an initial size to avoid resizing too often?

[Kevin Millikin (Chromium), 2010-03-24 07:50:45]

http://codereview.chromium.org/1159005/diff/1/2
File src/ast.cc (right):

http://codereview.chromium.org/1159005/diff/1/2#newcode647
src/ast.cc:647: return expression()->IsPrimitive();
On 2010/03/23 16:14:46, fschneider wrote:
> This should be 
> 
> return !expression()->IsPrimitive();
> 
> right?

Yes, good catch.

http://codereview.chromium.org/1159005/diff/1/5
File src/data-flow.cc (right):

http://codereview.chromium.org/1159005/diff/1/5#newcode2082
src/data-flow.cc:2082: List<AstNode*> stack;
On 2010/03/23 16:14:46, fschneider wrote:
> Maybe set an initial size to avoid resizing too often?

OK, I gave it 20.

[fschneider, 2010-03-24 09:27:28]

LGTM.