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| 1 // Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file | |
| 2 // for details. All rights reserved. Use of this source code is governed by a | |
| 3 // BSD-style license that can be found in the LICENSE file. | |
| 4 library dart2js.cps_ir.duplicate_branch; // FIXME: Rename file. | |
| 5 | |
| 6 import 'cps_ir_nodes.dart'; | |
| 7 import 'optimizers.dart'; | |
| 8 import 'cps_fragment.dart'; | |
| 9 import '../js_backend/js_backend.dart'; | |
| 10 import '../constants/values.dart'; | |
| 11 import '../elements/elements.dart'; | |
| 12 import '../universe/selector.dart'; | |
| 13 import '../types/types.dart'; | |
| 14 import 'type_mask_system.dart'; | |
| 15 | |
| 16 /// Optimizations based on intraprocedural forward dataflow analysis, taking | |
| 17 /// into account path information that is not expressed by [Refinement] nodes. | |
| 18 /// | |
| 19 /// --- | |
| 20 /// | |
| 21 /// Removes branches that branch on the same value as a previously seen branch. | |
| 22 /// For example: | |
| 23 /// | |
| 24 /// if (x == y) { | |
| 25 /// if (x == y) TRUE else FALSE | |
| 26 /// } | |
| 27 /// | |
| 28 /// ==> ([GVN] pass merges identical expressions) | |
| 29 /// | |
| 30 /// var b = (x == y) | |
| 31 /// if (b) { | |
| 32 /// if (b) TRUE else FALSE | |
| 33 /// } | |
| 34 /// | |
| 35 /// ==> (this pass removes the duplicate branch) | |
| 36 /// | |
| 37 /// var b = (x == y) | |
| 38 /// if (b) { | |
| 39 /// TRUE | |
| 40 /// } | |
| 41 /// | |
| 42 /// --- | |
| 43 /// | |
| 44 /// Removes interceptors for method calls whose receiver is known to be a | |
| 45 /// self-interceptor. For example: | |
| 46 /// | |
| 47 /// x.foo$1(); | |
| 48 /// getInterceptor(x).$eq(x, y); | |
| 49 /// | |
| 50 /// ==> (`x` is a self-interceptor, remove the `getInterceptor` call) | |
| 51 /// | |
| 52 /// x.foo$1(); | |
| 53 /// x.$eq(0, y); | |
| 54 /// | |
| 55 /// Although there is a [Refinement] node after the call to `x.foo$1()`, the | |
| 56 /// refined type cannot always be represented exactly, and type propagation | |
| 57 /// may therefore not see that `x` is a self-interceptor. | |
| 58 // | |
| 59 // TODO(asgerf): A kind of redundant join can arise where a branching condition | |
| 60 // is known to be true/false on all but one predecessor for a branch. We could | |
| 61 // try to reduce those. | |
| 62 // | |
| 63 // TODO(asgerf): Could be more precise if GVN shared expressions that are not | |
| 64 // in direct scope of one another, e.g. by using phis pass the shared value. | |
| 65 // | |
| 66 class PathBasedOptimizer extends TrampolineRecursiveVisitor | |
| 67 implements Pass { | |
| 68 String get passName => 'Path-based optimizations'; | |
| 69 | |
| 70 // Classification of all values. | |
| 71 static const int TRUE = 1 << 0; | |
| 72 static const int SELF_INTERCEPTOR = 1 << 1; | |
| 73 static const int INTERCEPTED_TRUTHY = 1 << 2; | |
| 74 static const int FALSE = 1 << 3; | |
| 75 static const int OTHER_FALSY = 1 << 4; | |
| 76 | |
| 77 static const int TRUTHY = TRUE | SELF_INTERCEPTOR | INTERCEPTED_TRUTHY; | |
| 78 static const int FALSY = FALSE | OTHER_FALSY; | |
| 79 static const int ANY = TRUTHY | FALSY; | |
| 80 | |
| 81 final JavaScriptBackend backend; | |
| 82 final TypeMaskSystem typeSystem; | |
| 83 | |
| 84 PathBasedOptimizer(this.backend, this.typeSystem); | |
| 85 | |
| 86 /// The possible values of the given primitive (or ANY if absent) at the | |
| 87 /// current traversal position. | |
| 88 Map<Primitive, int> valueOf = <Primitive, int>{}; | |
| 89 | |
| 90 /// The possible values of each primitive at the entry to a continuation. | |
| 91 /// | |
| 92 /// Unreachable continuations are absent from the map. | |
| 93 final Map<Continuation, Map<Primitive, int>> valuesAt = | |
| 94 <Continuation, Map<Primitive, int>>{}; | |
| 95 | |
| 96 void rewrite(FunctionDefinition node) { | |
| 97 visit(node); | |
| 98 } | |
| 99 | |
| 100 Map<Primitive, int> copy(Map<Primitive, int> map) { | |
| 101 return new Map<Primitive, int>.from(map); | |
| 102 } | |
| 103 | |
| 104 Expression traverseLetHandler(LetHandler node) { | |
| 105 valuesAt[node.handler] = copy(valueOf); | |
| 106 push(node.handler); | |
| 107 return node.body; | |
| 108 } | |
| 109 | |
| 110 Expression traverseContinuation(Continuation cont) { | |
| 111 valueOf = valuesAt[cont]; | |
| 112 if (valueOf == null) { | |
| 113 // Do not go into unreachable code. | |
| 114 destroyAndReplace(cont.body, new Unreachable()); | |
| 115 } | |
| 116 return cont.body; | |
| 117 } | |
| 118 | |
| 119 void visitInvokeContinuation(InvokeContinuation node) { | |
| 120 Continuation cont = node.continuation.definition; | |
| 121 if (cont.isReturnContinuation) return; | |
| 122 if (node.isRecursive) return; | |
| 123 Map<Primitive, int> target = valuesAt[cont]; | |
| 124 if (target == null) { | |
| 125 valuesAt[cont] = valueOf; | |
| 126 } else { | |
| 127 for (Primitive prim in target.keys) { | |
| 128 target[prim] |= valueOf[prim] ?? ANY; | |
| 129 } | |
| 130 } | |
| 131 } | |
| 132 | |
| 133 visitBranch(Branch node) { | |
| 134 Primitive condition = node.condition.definition.effectiveDefinition; | |
| 135 Continuation trueCont = node.trueContinuation.definition; | |
| 136 Continuation falseCont = node.falseContinuation.definition; | |
| 137 if (condition.hasExactlyOneUse) { | |
| 138 // Handle common case specially. Do not add [condition] to the map if | |
| 139 // there are no other uses. | |
| 140 valuesAt[trueCont] = copy(valueOf); | |
| 141 valuesAt[falseCont] = valueOf; | |
| 142 return; | |
| 143 } | |
| 144 int values = valueOf[condition] ?? ANY; | |
| 145 int positiveValues = node.isStrictCheck ? TRUE : TRUTHY; | |
| 146 int negativeValues = (~positiveValues) & ANY; | |
| 147 if (values & positiveValues == 0) { | |
| 148 destroyAndReplace(node, new InvokeContinuation(falseCont, [])); | |
| 149 valuesAt[falseCont] = valueOf; | |
| 150 } else if (values & negativeValues == 0) { | |
| 151 destroyAndReplace(node, new InvokeContinuation(trueCont, [])); | |
| 152 valuesAt[trueCont] = valueOf; | |
| 153 } else { | |
| 154 valuesAt[trueCont] = copy(valueOf)..[condition] = values & positiveValues; | |
| 155 valuesAt[falseCont] = valueOf..[condition] = values & negativeValues; | |
| 156 } | |
| 157 } | |
| 158 | |
| 159 void visitInvokeMethod(InvokeMethod node) { | |
| 160 int receiverValue = valueOf[node.dartReceiver] ?? ANY; | |
| 161 if (!backend.isInterceptedSelector(node.selector)) { | |
| 162 // Only self-interceptors can respond to a non-intercepted selector. | |
| 163 valueOf[node.dartReceiver] = receiverValue & SELF_INTERCEPTOR; | |
| 164 } else if (receiverValue & ~SELF_INTERCEPTOR == 0 && | |
| 165 node.callingConvention == CallingConvention.Intercepted) { | |
| 166 // This is an intercepted call whose receiver is definitely a | |
| 167 // self-interceptor. | |
| 168 // TODO(25646): If TypeMasks could represent "any self-interceptor" this | |
| 169 // optimization should be subsumed by type propagation. | |
| 170 node.receiver.changeTo(node.dartReceiver); | |
| 171 | |
| 172 // Replace the extra receiver argument with a dummy value if the | |
| 173 // target definitely does not use it. | |
| 174 if (typeSystem.targetIgnoresReceiverArgument(node.dartReceiver.type, | |
| 175 node.selector)) { | |
| 176 Constant dummy = new Constant(new IntConstantValue(0)) | |
| 177 ..type = typeSystem.intType; | |
| 178 new LetPrim(dummy).insertAbove(node.parent); | |
| 179 node.arguments[0].changeTo(dummy); | |
| 180 node.callingConvention = CallingConvention.DummyIntercepted; | |
| 181 } | |
| 182 } | |
| 183 } | |
| 184 } | |
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Chromium Code Reviews
Issue 1709623002:
dart2js cps: Rename duplicate_branch.dart to match the new pass name. (Closed)
Base URL: git@github.com:dart-lang/sdk.git@master