dart2js cps: Do not propagate uses of loop variables past their update.

dart2js cps: Do not propagate uses of loop variables past their update.

Also some documentation specifying the SSA-like assumptions we make
about the input to StatementRewriter.

BUG=
R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/01d2d2cb7309a758da46414ec4e5f9956df02526

[asgerf, 2015-07-01 11:37:20]

asgerf@google.com changed reviewers:
+ kmillikin@google.com

[Kevin Millikin (Google), 2015-07-01 13:48:04]

LGTM.

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
File pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart (right):

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart:11: *
Translates out of SSA form into direct-style.
I would not contrast direct-style and SSA, they are orthogonal.  I don't really
know a good name for non-SSA, so maybe just:

"Translates out of SSA."

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart:17: * must be
non-complex. A [VariableUse] and [This] is a non-complex expression.
non-complex == simple.  In CPS, sometimes the terms are "trivial" and "serious".

[asgerf, 2015-07-01 14:04:17]

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
File pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart (right):

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart:11: *
Translates out of SSA form into direct-style.
On 2015/07/01 13:48:04, Kevin Millikin (Google) wrote:
> I would not contrast direct-style and SSA, they are orthogonal.  I don't
really
> know a good name for non-SSA, so maybe just:
> 
> "Translates out of SSA."

Yeah that was wrong. I changed it to say direct-style, since that's the actual
job of this phase.

It's not clear what "out of SSA" means when there were no phi nodes to being
with.

For a while I've wanted to rename this phase to DirectStyleRewriter. The current
name is horrible.

https://codereview.chromium.org/1215503012/diff/40001/pkg/compiler/lib/src/tr...
pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart:17: * must be
non-complex. A [VariableUse] and [This] is a non-complex expression.
On 2015/07/01 13:48:04, Kevin Millikin (Google) wrote:
> non-complex == simple.  In CPS, sometimes the terms are "trivial" and
"serious".

Done.

[asgerf, 2015-07-02 13:15:08]

Committed patchset #5 (id:80001) manually as
01d2d2cb7309a758da46414ec4e5f9956df02526 (presubmit successful).