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