Compute the swap temporary to not clash with parameter names.

Compute the swap temporary to not clash with parameter names.
Committed: https://code.google.com/p/dart/source/detail?r=8385

[Lasse Reichstein Nielsen, 2012-06-07 08:53:21]

This CL doesn't seem to have a patch for tracer.dart?

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
File dart/lib/compiler/implementation/ssa/variable_allocator.dart (right):

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:360: Set<String>
parameters = new Set<String>.from(parameterNames.getValues());
Can't you use this.names somehow, since it's initialized with the parameter
names? I guess we don't want to conflict with any name, not just parameters.
That would also avoid having an extra field for parameterNames.

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:426: while
(usedNames.contains(name)) name = 't${i++}';
This looks like something that has quadratic performance in the number of
allocated temporaries. How about storing i between calls?

[ngeoffray, 2012-06-07 09:10:41]

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
File dart/lib/compiler/implementation/ssa/variable_allocator.dart (right):

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:360: Set<String>
parameters = new Set<String>.from(parameterNames.getValues());
On 2012/06/07 08:53:21, Lasse Reichstein Nielsen wrote:
> Can't you use this.names somehow, since it's initialized with the parameter
> names? I guess we don't want to conflict with any name, not just parameters.
> That would also avoid having an extra field for parameterNames.

As discussed, there is no extra field in this class. And parameterNames is used
by VariableNames and VariableNamer.

https://chromiumcodereview.appspot.com/10543050/diff/1/dart/lib/compiler/impl...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:426: while
(usedNames.contains(name)) name = 't${i++}';
On 2012/06/07 08:53:21, Lasse Reichstein Nielsen wrote:
> This looks like something that has quadratic performance in the number of
> allocated temporaries. How about storing i between calls?

Good point. Done.

[floitsch, 2012-06-07 09:27:32]

LGTM.

https://chromiumcodereview.appspot.com/10543050/diff/2002/dart/lib/compiler/i...
File dart/lib/compiler/implementation/ssa/variable_allocator.dart (right):

https://chromiumcodereview.appspot.com/10543050/diff/2002/dart/lib/compiler/i...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:425: String name =
't${temporaryIndex++}';
I thought we wanted to avoid this, because variables can become free.

[ngeoffray, 2012-06-07 09:33:45]

Thanks Florian and Lasse.

https://chromiumcodereview.appspot.com/10543050/diff/2002/dart/lib/compiler/i...
File dart/lib/compiler/implementation/ssa/variable_allocator.dart (right):

https://chromiumcodereview.appspot.com/10543050/diff/2002/dart/lib/compiler/i...
dart/lib/compiler/implementation/ssa/variable_allocator.dart:425: String name =
't${temporaryIndex++}';
On 2012/06/07 09:27:32, floitsch wrote:
> I thought we wanted to avoid this, because variables can become free.

It's ok on one instance of a VariableNamer because there is one VariableNamer
per block.