Eliminate branches on constant conditions during codegen.

Eliminate branches on constant conditions during codegen.

Committed: https://code.google.com/p/dart/source/detail?r=6033

[ahe, 2012-03-30 12:48:50]

Saves 10% output size of stress test (only 4% without speculative
optimizations).

[Lasse Reichstein Nielsen, 2012-03-30 12:56:02]

LGTM

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
File dart/lib/compiler/implementation/ssa/codegen.dart (right):

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:906: int preVisitedBlocks = 1;
I'd actually prefer to initialize it to zero, and only set it to 1 or 2 (or
increment it) after *actually* visiting the block.

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:909: if (false &&
condition.isConstant()) {
"false &&"?

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:912:
visitSubGraph(info.thenGraph);
Increment preVisitedBlocks here, or set it to 1, or do that in an else branch of
the following 'if'.

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:917: preVisitedBlocks = 2;
Here you set it to 1 (possibly with comment about skipping the then-branch).

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:918:
visitSubGraph(info.elseGraph);
And to 2 after visiting the else-part.

[ahe, 2012-03-30 13:15:52]

Thank you, Lasse.

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
File dart/lib/compiler/implementation/ssa/codegen.dart (right):

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:906: int preVisitedBlocks = 1;
On 2012/03/30 12:56:02, Lasse Reichstein Nielsen wrote:
> I'd actually prefer to initialize it to zero, and only set it to 1 or 2 (or
> increment it) after *actually* visiting the block.

Done.

https://chromiumcodereview.appspot.com/9950014/diff/1/dart/lib/compiler/imple...
dart/lib/compiler/implementation/ssa/codegen.dart:909: if (false &&
condition.isConstant()) {
On 2012/03/30 12:56:02, Lasse Reichstein Nielsen wrote:
> "false &&"?

Done.