Initial implementation of an edge-labeled instruction flow graph.

Initial implementation of an edge-labeled instruction flow graph.

The flow graph is built by walking the AST.  Edges are labeled with
instructions (AST nodes).  Normal nodes have a single predecessor edge and a
single (labeled) successor edge.  Branch nodes are explicit, they have a
single predecessor edge and a pair of (unlabeled) successor edges.  Merge
nodes are explicit, they have a pair of predecessor edges and a single
(unlabeled) successor edge.

There is a distinguished (normal) entry node and a distinguished (special)
exit node with arbitrarily many predecessor edges and no successor edges.

The graph is intended to support graph-based analysis and transformation.

Committed: http://code.google.com/p/v8/source/detail?r=4051

[Kevin Millikin (Chromium), 2010-03-03 12:51:09]

Includes partial work-in-progress support for simple printing.

[Kevin Millikin (Chromium), 2010-03-05 13:43:08]

Please take a look.

[fschneider, 2010-03-08 12:14:26]

LGTM.

http://codereview.chromium.org/660449/diff/3007/3010
File src/data-flow.cc (right):

http://codereview.chromium.org/660449/diff/3007/3010#newcode736
src/data-flow.cc:736: prop->obj()->set_num(AstNode::kNoNumber);
We should remove depending on certain nodes having no number as a separate
change.

http://codereview.chromium.org/660449/diff/3007/3011
File src/data-flow.h (right):

http://codereview.chromium.org/660449/diff/3007/3011#newcode116
src/data-flow.h:116: void Append(AstNode* instruction);
I'm not sure if overloading the name Append helps readability. I'd prefer using
AppendInstruction, AppendNode, AppendFlowGraph.

http://codereview.chromium.org/660449/diff/3007/3011#newcode125
src/data-flow.h:125: // and merged, so the graph remains single-entry,
single-exit.
Maybe mentions that left is always the true-branch and right is the false
branch.

http://codereview.chromium.org/660449/diff/3007/3011#newcode165
src/data-flow.h:165: void MarkWith(bool mark) { mark_ = mark; }
Name this functions consistently with other accessors mark() and set_mark()