1/*
2 * Copyright (C) 2014-2016 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#if ENABLE(DFG_JIT)
29
30namespace JSC { namespace DFG {
31
32class AtTailAbstractState;
33class Graph;
34struct Node;
35
36// A *very* conservative approximation of whether or not a node could possibly exit. Usually
37// returns true except in cases where we obviously don't expect an exit.
38
39enum ExitMode {
40 // The node does not exit at all. This means that it's legal to eliminate the first store in a
41 // program like:
42 //
43 // global = 1 // first store
44 // DoesNotExit(); // let's assume that this also doesn't read "global"
45 // global = 2 // second store
46 //
47 // It's legal to eliminate the first one since nobody will see it; the second store is always
48 // executed right after.
49 DoesNotExit,
50
51 // The node will exit, but only by properly throwing exceptions. A proper exception throw will
52 // divert execution to the matching op_catch and will not reexecute the exit origin. This means
53 // that the store elimination optimization above would be illegal, but the following would be OK:
54 //
55 // SideEffect(..., exit: bc#42)
56 // ExitsForExceptions(..., exit: #bc42, ExitInvalid)
57 //
58 // In particular, it's OK for a node that reports ExitsForExceptions to be executed in a context
59 // where !Node::origin.exitOK. That's because this node will not exit in a manner that could lead
60 // to the reexecution of SideEffect().
61 ExitsForExceptions,
62
63 // The node will exit to the exit origin. This means that we cannot do store elimination like for
64 // DoesNotExit and also we cannot place this node in an ExitInvalid context, since this will exit
65 // in a manner that will cause the reexecution of all previous operations within this exit origin.
66 Exits
67};
68
69// FIXME: This currently consumes the Check: flag produced by AI, and will claim that something doesn't
70// exit if the Check: flag was cleared. This makes it hard to use mayExit() for things like hoisting
71// (for example in LICM), since that wants to know if the node would exit if it was moved somewhere
72// else.
73// https://bugs.webkit.org/show_bug.cgi?id=148545
74
75ExitMode mayExit(Graph&, Node*);
76
77// Like mayExit(), but instead of using the Check: flag to determine if something exits, it
78// evaluates whether it will exit based on the tail state. This is useful for LICM. This *may* also
79// use the AtTailAbstractState to return more precise answers for other nodes.
80ExitMode mayExit(Graph&, Node*, AtTailAbstractState&);
81
82} } // namespace JSC::DFG
83
84namespace WTF {
85
86class PrintStream;
87
88void printInternal(PrintStream&, JSC::DFG::ExitMode);
89
90} // namespace WTF
91
92#endif // ENABLE(DFG_JIT)
93