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
|
/*
* Copyright 2017 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <wasm.h>
#include <pass.h>
#include <ir/properties.h>
namespace wasm {
// Adjust load signedness based on usage. If a load only has uses that sign or
// unsign it anyhow, then it could be either, and picking the popular one can
// help remove the most sign/unsign operations
// unsigned, then it could be either
struct PickLoadSigns : public WalkerPass<ExpressionStackWalker<PickLoadSigns>> {
bool isFunctionParallel() override { return true; }
Pass* create() override { return new PickLoadSigns; }
struct Usage {
Index signedUsages = 0;
Index signedBits;
Index unsignedUsages = 0;
Index unsignedBits;
Index totalUsages = 0;
};
std::vector<Usage> usages; // local index => usage
std::unordered_map<Load*, Index> loads; // loads that write to a local => the local
void doWalkFunction(Function* func) {
// prepare
usages.resize(func->getNumLocals());
// walk
ExpressionStackWalker<PickLoadSigns>::doWalkFunction(func);
// optimize
optimize();
}
void visitGetLocal(GetLocal* curr) {
// this is a use. check from the context what it is, signed or unsigned, etc.
auto& usage = usages[curr->index];
usage.totalUsages++;
if (expressionStack.size() >= 2) {
auto* parent = expressionStack[expressionStack.size() - 2];
if (Properties::getZeroExtValue(parent)) {
auto bits = Properties::getZeroExtBits(parent);
if (usage.unsignedUsages == 0) {
usage.unsignedBits = bits;
} else if (usage.unsignedBits != bits) {
usage.unsignedBits = 0;
}
usage.unsignedUsages++;
} else if (expressionStack.size() >= 3) {
auto* grandparent = expressionStack[expressionStack.size() - 3];
if (Properties::getSignExtValue(grandparent)) {
auto bits = Properties::getSignExtBits(grandparent);
if (usage.signedUsages == 0) {
usage.signedBits = bits;
} else if (usage.signedBits != bits) {
usage.signedBits = 0;
}
usage.signedUsages++;
}
}
}
}
void visitSetLocal(SetLocal* curr) {
if (curr->isTee()) {
// we can't modify a tee, the value is used elsewhere
return;
}
if (auto* load = curr->value->dynCast<Load>()) {
loads[load] = curr->index;
}
}
void optimize() {
// optimize based on the info we saw
for (auto& pair : loads) {
auto* load = pair.first;
auto index = pair.second;
auto& usage = usages[index];
// if we can't optimize, give up
if (usage.totalUsages == 0 || // no usages, so no idea
usage.signedUsages + usage.unsignedUsages != usage.totalUsages || // non-sign/unsigned usages, so cannot change
(usage.signedUsages != 0 && usage.signedBits != load->bytes * 8) || // sign usages exist but the wrong size
(usage.unsignedUsages != 0 && usage.unsignedBits != load->bytes * 8)) { // unsigned usages exist but the wrong size
continue;
}
// we can pick the optimal one. our hope is to remove 2 items per
// signed use (two shifts), so we factor that in
load->signed_ = usage.signedUsages * 2 >= usage.unsignedUsages;
}
}
};
Pass *createPickLoadSignsPass() {
return new PickLoadSigns();
}
} // namespace wasm
|
