1 // Copyright 2015 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/tail-call-optimization.h"
6
7 #include "src/compiler/common-operator.h"
8 #include "src/compiler/graph.h"
9 #include "src/compiler/linkage.h"
10 #include "src/compiler/node-properties.h"
11
12 namespace v8 {
13 namespace internal {
14 namespace compiler {
15
Reduce(Node * node)16 Reduction TailCallOptimization::Reduce(Node* node) {
17 if (node->opcode() != IrOpcode::kReturn) return NoChange();
18 // The value which is returned must be the result of a potential tail call,
19 // there must be no try/catch/finally around the Call, and there must be no
20 // other effect between the Call and the Return nodes.
21 Node* const call = NodeProperties::GetValueInput(node, 0);
22 if (call->opcode() == IrOpcode::kCall &&
23 OpParameter<CallDescriptor const*>(call)->SupportsTailCalls() &&
24 NodeProperties::GetEffectInput(node) == call &&
25 !NodeProperties::IsExceptionalCall(call)) {
26 Node* const control = NodeProperties::GetControlInput(node);
27 if (control->opcode() == IrOpcode::kIfSuccess &&
28 call->OwnedBy(node, control) && control->OwnedBy(node)) {
29 // Furthermore, control has to flow via an IfSuccess from the Call, so
30 // the Return node value and effect depends directly on the Call node,
31 // and indirectly control depends on the Call via an IfSuccess.
32
33 // Value1 ... ValueN Effect Control
34 // ^ ^ ^ ^
35 // | | | |
36 // | +--+ +-+ |
37 // +----------+ | | +------+
38 // \ | | /
39 // Call[Descriptor]
40 // ^ ^ ^
41 // | | |
42 // +-+ | |
43 // | | |
44 // | +-+ |
45 // | | IfSuccess
46 // | | ^
47 // | | |
48 // Return
49 // ^
50 // |
51
52 // The resulting graph looks like this:
53
54 // Value1 ... ValueN Effect Control
55 // ^ ^ ^ ^
56 // | | | |
57 // | +--+ +-+ |
58 // +----------+ | | +------+
59 // \ | | /
60 // TailCall[Descriptor]
61 // ^
62 // |
63
64 DCHECK_EQ(call, NodeProperties::GetControlInput(control, 0));
65 DCHECK_EQ(3, node->InputCount());
66 node->ReplaceInput(0, NodeProperties::GetEffectInput(call));
67 node->ReplaceInput(1, NodeProperties::GetControlInput(call));
68 node->RemoveInput(2);
69 for (int index = 0; index < call->op()->ValueInputCount(); ++index) {
70 node->InsertInput(graph()->zone(), index,
71 NodeProperties::GetValueInput(call, index));
72 }
73 NodeProperties::ChangeOp(
74 node, common()->TailCall(OpParameter<CallDescriptor const*>(call)));
75 return Changed(node);
76 }
77 }
78 return NoChange();
79 }
80
81 } // namespace compiler
82 } // namespace internal
83 } // namespace v8
84