Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame^] | 1 | // Copyright 2014 the V8 project authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #include "src/compiler/common-operator.h" |
| 6 | #include "src/compiler/generic-node-inl.h" |
| 7 | #include "src/compiler/graph-inl.h" |
| 8 | #include "src/compiler/js-context-specialization.h" |
| 9 | #include "src/compiler/js-operator.h" |
| 10 | #include "src/compiler/node-aux-data-inl.h" |
| 11 | #include "src/compiler/node-matchers.h" |
| 12 | #include "src/compiler/node-properties-inl.h" |
| 13 | |
| 14 | namespace v8 { |
| 15 | namespace internal { |
| 16 | namespace compiler { |
| 17 | |
| 18 | class ContextSpecializationVisitor : public NullNodeVisitor { |
| 19 | public: |
| 20 | explicit ContextSpecializationVisitor(JSContextSpecializer* spec) |
| 21 | : spec_(spec) {} |
| 22 | |
| 23 | GenericGraphVisit::Control Post(Node* node) { |
| 24 | switch (node->opcode()) { |
| 25 | case IrOpcode::kJSLoadContext: { |
| 26 | Reduction r = spec_->ReduceJSLoadContext(node); |
| 27 | if (r.Changed() && r.replacement() != node) { |
| 28 | NodeProperties::ReplaceWithValue(node, r.replacement()); |
| 29 | node->RemoveAllInputs(); |
| 30 | } |
| 31 | break; |
| 32 | } |
| 33 | case IrOpcode::kJSStoreContext: { |
| 34 | Reduction r = spec_->ReduceJSStoreContext(node); |
| 35 | if (r.Changed() && r.replacement() != node) { |
| 36 | NodeProperties::ReplaceWithValue(node, r.replacement()); |
| 37 | node->RemoveAllInputs(); |
| 38 | } |
| 39 | break; |
| 40 | } |
| 41 | default: |
| 42 | break; |
| 43 | } |
| 44 | return GenericGraphVisit::CONTINUE; |
| 45 | } |
| 46 | |
| 47 | private: |
| 48 | JSContextSpecializer* spec_; |
| 49 | }; |
| 50 | |
| 51 | |
| 52 | void JSContextSpecializer::SpecializeToContext() { |
| 53 | NodeProperties::ReplaceWithValue(context_, |
| 54 | jsgraph_->Constant(info_->context())); |
| 55 | |
| 56 | ContextSpecializationVisitor visitor(this); |
| 57 | jsgraph_->graph()->VisitNodeInputsFromEnd(&visitor); |
| 58 | } |
| 59 | |
| 60 | |
| 61 | Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) { |
| 62 | DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode()); |
| 63 | |
| 64 | HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0)); |
| 65 | // If the context is not constant, no reduction can occur. |
| 66 | if (!m.HasValue()) { |
| 67 | return Reducer::NoChange(); |
| 68 | } |
| 69 | |
| 70 | ContextAccess access = OpParameter<ContextAccess>(node); |
| 71 | |
| 72 | // Find the right parent context. |
| 73 | Context* context = *m.Value().handle(); |
| 74 | for (int i = access.depth(); i > 0; --i) { |
| 75 | context = context->previous(); |
| 76 | } |
| 77 | |
| 78 | // If the access itself is mutable, only fold-in the parent. |
| 79 | if (!access.immutable()) { |
| 80 | // The access does not have to look up a parent, nothing to fold. |
| 81 | if (access.depth() == 0) { |
| 82 | return Reducer::NoChange(); |
| 83 | } |
| 84 | const Operator* op = jsgraph_->javascript()->LoadContext( |
| 85 | 0, access.index(), access.immutable()); |
| 86 | node->set_op(op); |
| 87 | Handle<Object> context_handle = Handle<Object>(context, info_->isolate()); |
| 88 | node->ReplaceInput(0, jsgraph_->Constant(context_handle)); |
| 89 | return Reducer::Changed(node); |
| 90 | } |
| 91 | Handle<Object> value = |
| 92 | Handle<Object>(context->get(access.index()), info_->isolate()); |
| 93 | |
| 94 | // Even though the context slot is immutable, the context might have escaped |
| 95 | // before the function to which it belongs has initialized the slot. |
| 96 | // We must be conservative and check if the value in the slot is currently the |
| 97 | // hole or undefined. If it is neither of these, then it must be initialized. |
| 98 | if (value->IsUndefined() || value->IsTheHole()) { |
| 99 | return Reducer::NoChange(); |
| 100 | } |
| 101 | |
| 102 | // Success. The context load can be replaced with the constant. |
| 103 | // TODO(titzer): record the specialization for sharing code across multiple |
| 104 | // contexts that have the same value in the corresponding context slot. |
| 105 | return Reducer::Replace(jsgraph_->Constant(value)); |
| 106 | } |
| 107 | |
| 108 | |
| 109 | Reduction JSContextSpecializer::ReduceJSStoreContext(Node* node) { |
| 110 | DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode()); |
| 111 | |
| 112 | HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0)); |
| 113 | // If the context is not constant, no reduction can occur. |
| 114 | if (!m.HasValue()) { |
| 115 | return Reducer::NoChange(); |
| 116 | } |
| 117 | |
| 118 | ContextAccess access = OpParameter<ContextAccess>(node); |
| 119 | |
| 120 | // The access does not have to look up a parent, nothing to fold. |
| 121 | if (access.depth() == 0) { |
| 122 | return Reducer::NoChange(); |
| 123 | } |
| 124 | |
| 125 | // Find the right parent context. |
| 126 | Context* context = *m.Value().handle(); |
| 127 | for (int i = access.depth(); i > 0; --i) { |
| 128 | context = context->previous(); |
| 129 | } |
| 130 | |
| 131 | const Operator* op = jsgraph_->javascript()->StoreContext(0, access.index()); |
| 132 | node->set_op(op); |
| 133 | Handle<Object> new_context_handle = Handle<Object>(context, info_->isolate()); |
| 134 | node->ReplaceInput(0, jsgraph_->Constant(new_context_handle)); |
| 135 | |
| 136 | return Reducer::Changed(node); |
| 137 | } |
| 138 | |
| 139 | } // namespace compiler |
| 140 | } // namespace internal |
| 141 | } // namespace v8 |