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dart2js cps: Change type tests to null tests when applicable.

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When null is the only value that might fail a type test we can
rewrite it to just compare against null.

R=kmillikin@google.com, sra@google.com

Review URL: https://codereview.chromium.org//1306773005 .
This commit is contained in:
Asger Feldthaus 2015-09-21 13:33:16 +02:00
parent 2bbf0c61ae
commit 29dedfa97e
1 changed files with 21 additions and 1 deletions
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22
pkg/compiler/lib/src/cps_ir/type_propagation.dart
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@ -43,12 +43,15 @@ class ConstantPropagationLattice {
final ConstantSystem constantSystem;
final types.DartTypes dartTypes;
final AbstractValue anything;
final AbstractValue nullValue;
ConstantPropagationLattice(TypeMaskSystem typeSystem,
this.constantSystem,
this.dartTypes)
: this.typeSystem = typeSystem,
anything = new AbstractValue.nonConstant(typeSystem.dynamicType);
anything = new AbstractValue.nonConstant(typeSystem.dynamicType),
nullValue = new AbstractValue.constantValue(
new NullConstantValue(), new TypeMask.empty());
final AbstractValue nothing = new AbstractValue.nothing();
@ -1830,6 +1833,23 @@ class TransformingVisitor extends LeafVisitor {
<Primitive>[prim],
node.sourceInformation);
}
AbstractBool isNullableSubtype =
lattice.isSubtypeOf(value, node.dartType, allowNull: true);
AbstractBool isNullPassingTest =
lattice.isSubtypeOf(lattice.nullValue, node.dartType);
if (isNullableSubtype == AbstractBool.True &&
isNullPassingTest == AbstractBool.False) {
// Null is the only value not satisfying the type test.
// Replace the type test with a null-check.
// This has lower priority than the 'typeof'-based tests because
// 'typeof' expressions might give the VM some more useful information.
Primitive nullConst = makeConstantPrimitive(new NullConstantValue());
insertLetPrim(node.parent, nullConst);
return new ApplyBuiltinOperator(
BuiltinOperator.LooseNeq,
<Primitive>[prim, nullConst],
node.sourceInformation);
}
return null;
}