Split the AST LoopStatement type into separate types for do/while,...

Split the AST LoopStatement type into separate types for do/while,
while, and for loops.

Previously they were distinguished by a type field, which required
runtime asserts to avoid invalid nodes (since not all loop types have
the same internal structure).  Now they C++ type system is used to
require well-formed loop ASTs.

Because they do not share compilation code, we had very large
functions in the code generators that merely did a runtime dispatch to
a specific implementation based on the type.

Committed: http://code.google.com/p/v8/source/detail?r=3048

[William Hesse, 2009-10-12 11:45:35]

LGTM.

http://codereview.chromium.org/269049/diff/1/15
File src/parser.cc (right):

http://codereview.chromium.org/269049/diff/1/15#newcode2613
Line 2613: Statement* Parser::ParseForStatement(ZoneStringList* labels, bool*
ok) {
Perhaps there should be a comment saying that this returns a ForStatement or a
ForInStatement.

http://codereview.chromium.org/269049/diff/1/2
File src/prettyprinter.cc (right):

http://codereview.chromium.org/269049/diff/1/2#newcode181
Line 181: Visit(node->next());  // prints extra ';', unfortunately
I don't understand this comment.

[fschneider, 2009-10-12 12:10:21]

LGTM.