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Improve condition strengthening for last test in short-circuit.

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This strengthens

   t1 = s == null || t == null;
   if (t1) return;
   known-here:  t != null

There are not many hits since the 'interesting' tests are usually
earlier in the short-circuit expression.

R=sigmund@google.com

Review URL: https://codereview.chromium.org/2438543004 .
This commit is contained in:
Stephen Adams 2016-10-25 04:48:35 -07:00
parent 6e6ff496ed
commit 7eaad70e2f
1 changed files with 41 additions and 32 deletions
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73
pkg/compiler/lib/src/ssa/optimize.dart
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@ -2110,29 +2110,22 @@ class SsaTypeConversionInserter extends HBaseVisitor
return;
}
List<HInstruction> ifUsers = <HInstruction>[];
List<HInstruction> notIfUsers = <HInstruction>[];
List<HBasicBlock> trueTargets = <HBasicBlock>[];
List<HBasicBlock> falseTargets = <HBasicBlock>[];
collectIfUsers(instruction, ifUsers, notIfUsers);
collectTargets(instruction, trueTargets, falseTargets);
if (ifUsers.isEmpty && notIfUsers.isEmpty) return;
if (trueTargets.isEmpty && falseTargets.isEmpty) return;
TypeMask convertedType =
new TypeMask.nonNullSubtype(element, compiler.closedWorld);
HInstruction input = instruction.expression;
for (HIf ifUser in ifUsers) {
insertTypePropagationForDominatedUsers(
ifUser.thenBlock, input, convertedType);
// TODO(ngeoffray): Also change uses for the else block on a type
// that knows it is not of a specific type.
}
for (HIf ifUser in notIfUsers) {
insertTypePropagationForDominatedUsers(
ifUser.elseBlock, input, convertedType);
// TODO(ngeoffray): Also change uses for the then block on a type
// that knows it is not of a specific type.
for (HBasicBlock block in trueTargets) {
insertTypePropagationForDominatedUsers(block, input, convertedType);
}
// TODO(sra): Also strengthen uses for when the condition is known
// false. Avoid strengthening to `null`.
}
void visitIdentity(HIdentity instruction) {
@ -2151,34 +2144,50 @@ class SsaTypeConversionInserter extends HBaseVisitor
if (!input.instructionType.isNullable) return;
List<HInstruction> ifUsers = <HInstruction>[];
List<HInstruction> notIfUsers = <HInstruction>[];
List<HBasicBlock> trueTargets = <HBasicBlock>[];
List<HBasicBlock> falseTargets = <HBasicBlock>[];
collectIfUsers(instruction, ifUsers, notIfUsers);
collectTargets(instruction, trueTargets, falseTargets);
if (ifUsers.isEmpty && notIfUsers.isEmpty) return;
if (trueTargets.isEmpty && falseTargets.isEmpty) return;
TypeMask nonNullType = input.instructionType.nonNullable();
for (HIf ifUser in ifUsers) {
insertTypePropagationForDominatedUsers(
ifUser.elseBlock, input, nonNullType);
// Uses in thenBlock are `null`, but probably not common.
}
for (HIf ifUser in notIfUsers) {
insertTypePropagationForDominatedUsers(
ifUser.thenBlock, input, nonNullType);
// Uses in elseBlock are `null`, but probably not common.
for (HBasicBlock block in falseTargets) {
insertTypePropagationForDominatedUsers(block, input, nonNullType);
}
// We don't strengthen the known-true references. It doesn't happen often
// and we don't want "if (x==null) return x;" to convert between JavaScript
// 'null' and 'undefined'.
}
collectIfUsers(HInstruction instruction, List<HInstruction> ifUsers,
List<HInstruction> notIfUsers) {
collectTargets(HInstruction instruction, List<HBasicBlock> trueTargets,
List<HBasicBlock> falseTargets) {
for (HInstruction user in instruction.usedBy) {
if (user is HIf) {
ifUsers.add(user);
trueTargets?.add(user.thenBlock);
falseTargets?.add(user.elseBlock);
} else if (user is HNot) {
collectIfUsers(user, notIfUsers, ifUsers);
collectTargets(user, falseTargets, trueTargets);
} else if (user is HPhi) {
List<HInstruction> inputs = user.inputs;
if (inputs.length == 2) {
assert(inputs.contains(instruction));
HInstruction other = inputs[(inputs[0] == instruction) ? 1 : 0];
if (other.isConstantTrue()) {
// The condition flows to a HPhi(true, user), which means that a
// downstream HIf has true-branch control flow that does not depend
// on the original instruction, so stop collecting [trueTargets].
collectTargets(user, null, falseTargets);
} else if (other.isConstantFalse()) {
// Ditto for false.
collectTargets(user, trueTargets, null);
}
}
} else if (user is HBoolify) {
// We collect targets for strictly boolean operations so HBoolify cannot
// change the result.
collectTargets(user, trueTargets, falseTargets);
}
}
}