Repository navigation
Expand file tree
/
Copy pathB3HoistLoopInvariantValues.cpp
More file actions
251 lines (214 loc) · 9.72 KB
/
Copy pathB3HoistLoopInvariantValues.cpp
File metadata and controls
251 lines (214 loc) · 9.72 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
/*
* Copyright (C) 2017 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "B3HoistLoopInvariantValues.h"
#if ENABLE(B3_JIT)
#include "B3BackwardsDominators.h"
#include "B3Dominators.h"
#include "B3EnsureLoopPreHeaders.h"
#include "B3NaturalLoops.h"
#include "B3PhaseScope.h"
#include "B3ProcedureInlines.h"
#include "B3ValueInlines.h"
#include <wtf/RangeSet.h>
namespace JSC { namespace B3 {
// A load that can trap reports exitsSideways, which normally disqualifies it from hoisting. The
// fault is its only escaping effect, so it can still move to a point where it is certain to run and
// where nothing observable precedes it. WasmGC field and length loads depend on this: their null
// check is a trap rather than a branch, which would otherwise be all that blocks hoisting them.
static bool isTrappingLoad(const Value* value)
{
if (!value->traps())
return false;
switch (value->opcode()) {
case Load8Z:
case Load8S:
case Load16Z:
case Load16S:
case Load:
// A fenced load also orders memory, which is an effect that cannot move.
return !value->as<MemoryValue>()->hasFence();
case WasmStructGet:
case WasmArrayLength:
return true;
default:
return false;
}
}
static bool isReachedWithoutTrapBarrier(const NaturalLoops& loops, const NaturalLoop& loop, BasicBlock* block, const IndexSet<BasicBlock*>& blockBarriers)
{
if (block == loop.header())
return true;
// Tracing ancestors from the block. If any blocks belonging to this loop has a trap,
// then we cannot hoist since that trap needs to be executed before the hoisted value causes
// a trap at a pre-header block.
Vector<BasicBlock*, 8> worklist;
IndexSet<BasicBlock*> seen;
auto push = [&](BasicBlock* predecessor) {
if (loops.belongsTo(predecessor, loop)) {
if (seen.add(predecessor)) {
// Every value in these blocks runs before the one being hoisted.
if (blockBarriers.contains(predecessor))
return false;
// Stopping at the header is enough even though earlier iterations run other blocks:
// callers only reach here for a value whose block backwards-dominates the pre-header,
// and backwards dominance counts a back edge as a way for the procedure to end, so
// such a value always runs before any iteration completes.
if (predecessor == loop.header())
return true;
worklist.append(predecessor);
}
}
return true;
};
for (BasicBlock* predecessor : block->predecessors()) {
if (!push(predecessor))
return false;
}
while (!worklist.isEmpty()) {
BasicBlock* current = worklist.takeLast();
for (BasicBlock* predecessor : current->predecessors()) {
if (!push(predecessor))
return false;
}
}
return true;
}
bool hoistLoopInvariantValues(Procedure& proc)
{
PhaseScope phaseScope(proc, "hoistLoopInvariantValues"_s);
ensureLoopPreHeaders(proc);
NaturalLoops& loops = proc.naturalLoops();
if (!loops.numLoops())
return false;
proc.resetValueOwners();
Dominators& dominators = proc.dominators();
BackwardsDominators& backwardsDominators = proc.backwardsDominators();
// FIXME: We should have a reusable B3::EffectsSet data structure.
// https://bugs.webkit.org/show_bug.cgi?id=174762
struct LoopData {
RangeSet<HeapRange> writes;
bool writesLocalState { false };
bool writesPinned { false };
bool exitsSideways { false };
BasicBlock* preHeader { nullptr };
};
IndexMap<NaturalLoop, LoopData> data(loops.numLoops());
IndexSet<BasicBlock*> blockBarriers;
for (unsigned loopIndex = loops.numLoops(); loopIndex--;) {
const NaturalLoop& loop = loops.loop(loopIndex);
for (BasicBlock* predecessor : loop.header()->predecessors()) {
if (loops.belongsTo(predecessor, loop))
continue;
RELEASE_ASSERT(!data[loop].preHeader);
data[loop].preHeader = predecessor;
}
}
for (BasicBlock* block : proc) {
const NaturalLoop* loop = loops.innerMostLoopOf(block);
if (!loop)
continue;
for (Value* value : *block) {
Effects effects = value->effects();
data[*loop].writes.add(effects.writes);
data[*loop].writesLocalState |= effects.writesLocalState;
data[*loop].writesPinned |= effects.writesPinned;
data[*loop].exitsSideways |= effects.exitsSideways;
if (effects.isTrapBarrier())
blockBarriers.add(block);
}
}
for (unsigned loopIndex = loops.numLoops(); loopIndex--;) {
const NaturalLoop& loop = loops.loop(loopIndex);
for (const NaturalLoop* current = loops.innerMostOuterLoop(loop); current; current = loops.innerMostOuterLoop(*current)) {
data[*current].writes.addAll(data[loop].writes);
data[*current].writesLocalState |= data[loop].writesLocalState;
data[*current].writesPinned |= data[loop].writesPinned;
data[*current].exitsSideways |= data[loop].exitsSideways;
}
}
bool changed = false;
// Pre-order ensures that we visit our dominators before we visit ourselves. Otherwise we'd miss some
// hoisting opportunities in complex CFGs.
for (BasicBlock* block : proc.blocksInPreOrder()) {
Vector<const NaturalLoop*> blockLoops = loops.loopsOf(block);
if (blockLoops.isEmpty())
continue;
// Values that stay in this block run before everything later in it, so once one of them is a
// trap barrier nothing after it can be hoisted out on the strength of trapping first.
bool trapBarrierInBlock = false;
for (Value*& value : *block) {
Effects effects = value->effects();
bool trappingLoad = isTrappingLoad(value);
bool hoisted = false;
// We never hoist write effects or control constructs. A trapping load is allowed
// through. The fault it reports as a side exit is its own, and the checks below decide
// whether it may move.
if (!effects.mustExecute() || trappingLoad) {
// Try outermost loop first.
for (unsigned i = blockLoops.size(); i--;) {
const NaturalLoop& loop = *blockLoops[i];
bool ok = true;
for (Value* child : value->children()) {
if (!dominators.dominates(child->owner, data[loop].preHeader)) {
ok = false;
break;
}
}
if (!ok)
continue;
if (effects.controlDependent || trappingLoad) {
// The block is backward-dominating the pre-header.
// The value needs to be guaranteed to run on every iteration.
if (!backwardsDominators.dominates(block, data[loop].preHeader))
continue;
if (data[loop].exitsSideways) {
// Even if the loop can exit (after this value for example), if we do not have
// any exit between pre-header to this value, we can still hoist a value because
// this can be a first value causing a trap.
if (trapBarrierInBlock || !isReachedWithoutTrapBarrier(loops, loop, block, blockBarriers))
continue;
}
}
if (effects.readsPinned && data[loop].writesPinned)
continue;
if (effects.readsLocalState && data[loop].writesLocalState)
continue;
if (data[loop].writes.overlaps(effects.reads))
continue;
data[loop].preHeader->appendNonTerminal(value);
value = proc.add<Value>(Nop, Void, value->origin());
changed = true;
hoisted = true;
}
}
if (!hoisted)
trapBarrierInBlock |= effects.isTrapBarrier();
}
}
return changed;
}
} } // namespace JSC::B3
#endif // ENABLE(B3_JIT)