Introduce a nesting stack to the flow graph builder.

Introduce a nesting stack to the flow graph builder.

Statically track nested blocks, loops, and switches while constructing
the flow graph.  Use the nesting stack as a mapping from source labels
(class SourceLabel) to their flow-graph targets (class JoinEntryInstr).

This removes the indirect dependence of the AST on the intermediate
language and the mutable compiler state from the AST.

R=fschneider@google.com, srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=30336

[Kevin Millikin (Google), 2013-11-13 16:54:20]

This removes a longstanding TODO.  There is some unnecessary wartiness with
switch/case nodes but I'm leery of changing the AST or parser.

[srdjan, 2013-11-13 17:17:08]

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder.h
File runtime/vm/flow_graph_builder.h (right):

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.h:109: class NestedStatement;
Typically all forward class declarations are done in the beginning.

[Florian Schneider, 2013-11-13 17:42:58]

LGTM.

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder.cc
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.cc:1967: if (node->kind() == Token::kBREAK) {
For less duplicated code maybe move this condition inside the loop:

NestedStatement* current = owner()->nesting_stack();
while (current != NULL) {
  jump_target = node->kind() == Token::kBREAK
      ? current->BreakTargetFor(node->label())
      : current->ContinueTargetFor(node->label());
  if (jump_target != NULL) break;
  current = current->outer();
}

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder.h
File runtime/vm/flow_graph_builder.h (right):

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.h:226: class NestedStatement : public ValueObject
{
Do you actually need to declare NestedStatement here? If a forward decl is
enough, you could move the declaration to the .cc file where the subclasses
already are.

[Kevin Millikin (Google), 2013-11-13 17:47:21]

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder.cc
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.cc:1967: if (node->kind() == Token::kBREAK) {
On 2013/11/13 17:42:58, Florian Schneider wrote:
> For less duplicated code maybe move this condition inside the loop:
> 
> NestedStatement* current = owner()->nesting_stack();
> while (current != NULL) {
>   jump_target = node->kind() == Token::kBREAK
>       ? current->BreakTargetFor(node->label())
>       : current->ContinueTargetFor(node->label());
>   if (jump_target != NULL) break;
>   current = current->outer();
> }

That sounds good to me.  I'll do it.

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder.h
File runtime/vm/flow_graph_builder.h (right):

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.h:109: class NestedStatement;
On 2013/11/13 17:17:08, srdjan wrote:
> Typically all forward class declarations are done in the beginning. 

I'll move it.

https://codereview.chromium.org/71703002/diff/1/runtime/vm/flow_graph_builder...
runtime/vm/flow_graph_builder.h:226: class NestedStatement : public ValueObject
{
On 2013/11/13 17:42:58, Florian Schneider wrote:
> Do you actually need to declare NestedStatement here? If a forward decl is
> enough, you could move the declaration to the .cc file where the subclasses
> already are.

It does look like a forward declaration is enough.  I'll move it.

[srdjan, 2013-11-13 17:51:41]

lgtm

[Kevin Millikin (Google), 2013-11-18 11:39:22]

Committed patchset #1 manually as r30336 (presubmit successful).