Fix buggy computations in value ranges, spotted by floitsch@.

Fix buggy computations in value ranges, spotted by floitsch@.
Committed: https://code.google.com/p/dart/source/detail?r=13344

[floitsch, 2012-10-02 09:32:28]

FYI.
Please add a test for negative bit-ands.

http://codereview.chromium.org/11042002/diff/4001/lib/compiler/implementation...
File lib/compiler/implementation/ssa/value_range_analyzer.dart (right):

http://codereview.chromium.org/11042002/diff/4001/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:293: // Only operate
on simple operations, ie when one of the range is
There is no need to make this restriction.
if this.isPositive && other.isPositive: [0 .. max(upper, other.upper)];
if (this.isPositive): [0 .. upper]
if (other.isPositive): [0 .. other.upper]
You could also get better ranges when the ranges are negative, but I'm not sure
it's worth it. For example:
if this.isNegative && other.isNegative: [-infinity, max(upper, other.upper)].
And there is probably a way to make the -infinity go away.

http://codereview.chromium.org/11042002/diff/4001/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:297: else if
(isNegative()) return new Range(lower, const IntValue(0));
This is wrong: -1 & 5 -> 5

[ngeoffray, 2012-10-05 12:48:42]

I added a unit test for testing range operations. Soren, could you please take a
look since Florian is OOO?

[Søren Gjesse, 2012-10-08 06:49:38]

lgtm

[floitsch, 2012-10-10 15:19:59]

FYI.

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
File lib/compiler/implementation/ssa/value_range_analyzer.dart (right):

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:56: return new
OperationValue(this, other, const SubtractOperation());
you shouldn't use the operations directly but fetch them from the correct
system.

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:64: if
(other.isPositive()) return new IntValue(-value);
I don't think this is true.
-1 & FF => FF and not 1

[ngeoffray, 2012-10-15 12:17:23]

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
File lib/compiler/implementation/ssa/value_range_analyzer.dart (right):

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:56: return new
OperationValue(this, other, const SubtractOperation());
On 2012/10/10 15:19:59, floitsch wrote:
> you shouldn't use the operations directly but fetch them from the correct
> system.

I removed this code, so it's not a problem anymore.

http://codereview.chromium.org/11042002/diff/2002/lib/compiler/implementation...
lib/compiler/implementation/ssa/value_range_analyzer.dart:64: if
(other.isPositive()) return new IntValue(-value);
On 2012/10/10 15:19:59, floitsch wrote:
> I don't think this is true.
> -1 & FF => FF and not 1

Well spotted. Actually I think this is dead code, let me check and update the
code.