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
|
//===------------------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/DropUnnecessaryAssumes.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
using namespace llvm::PatternMatch;
static bool affectedValuesAreEphemeral(ArrayRef<Value *> Affected) {
// Check whether all the uses are ephemeral, i.e. recursively only used
// by assumes. In that case, the assume does not provide useful information.
// Note that additional users may appear as a result of inlining and CSE,
// so we should only make this assumption late in the optimization pipeline.
SmallSetVector<Instruction *, 32> Worklist;
auto AddUsers = [&](Value *V) {
for (User *U : V->users()) {
// Bail out if we need to inspect too many users.
if (Worklist.size() >= 32)
return false;
Worklist.insert(cast<Instruction>(U));
}
return true;
};
for (Value *V : Affected) {
// Do not handle assumes on globals for now. The use list for them may
// contain uses in other functions.
if (!isa<Instruction, Argument>(V))
return false;
if (!AddUsers(V))
return false;
}
for (unsigned Idx = 0; Idx < Worklist.size(); ++Idx) {
Instruction *I = Worklist[Idx];
// Use in assume is ephemeral.
if (isa<AssumeInst>(I))
continue;
// Use in side-effecting instruction is non-ephemeral.
if (I->mayHaveSideEffects() || I->isTerminator())
return false;
// Otherwise, recursively look at the users.
if (!AddUsers(I))
return false;
}
return true;
}
PreservedAnalyses
DropUnnecessaryAssumesPass::run(Function &F, FunctionAnalysisManager &FAM) {
AssumptionCache &AC = FAM.getResult<AssumptionAnalysis>(F);
bool Changed = false;
for (const WeakVH &Elem : AC.assumptions()) {
auto *Assume = cast_or_null<AssumeInst>(Elem);
if (!Assume)
continue;
if (Assume->hasOperandBundles()) {
// Handle operand bundle assumptions.
SmallVector<WeakTrackingVH> DeadBundleArgs;
SmallVector<OperandBundleDef> KeptBundles;
unsigned NumBundles = Assume->getNumOperandBundles();
for (unsigned I = 0; I != NumBundles; ++I) {
auto IsDead = [](OperandBundleUse Bundle) {
// "ignore" operand bundles are always dead.
if (Bundle.getTagName() == "ignore")
return true;
// Bundles without arguments do not affect any specific values.
// Always keep them for now.
if (Bundle.Inputs.empty())
return false;
SmallVector<Value *> Affected;
AssumptionCache::findValuesAffectedByOperandBundle(
Bundle, [&](Value *A) { Affected.push_back(A); });
return affectedValuesAreEphemeral(Affected);
};
OperandBundleUse Bundle = Assume->getOperandBundleAt(I);
if (IsDead(Bundle))
append_range(DeadBundleArgs, Bundle.Inputs);
else
KeptBundles.emplace_back(Bundle);
}
if (KeptBundles.size() != NumBundles) {
if (KeptBundles.empty()) {
// All operand bundles are dead, remove the whole assume.
Assume->eraseFromParent();
} else {
// Otherwise only drop the dead operand bundles.
CallBase *NewAssume =
CallBase::Create(Assume, KeptBundles, Assume->getIterator());
AC.registerAssumption(cast<AssumeInst>(NewAssume));
Assume->eraseFromParent();
}
RecursivelyDeleteTriviallyDeadInstructionsPermissive(DeadBundleArgs);
Changed = true;
}
continue;
}
Value *Cond = Assume->getArgOperand(0);
// Don't drop type tests, which have special semantics.
if (match(Cond, m_Intrinsic<Intrinsic::type_test>()))
continue;
SmallVector<Value *> Affected;
findValuesAffectedByCondition(Cond, /*IsAssume=*/true,
[&](Value *A) { Affected.push_back(A); });
if (!affectedValuesAreEphemeral(Affected))
continue;
Assume->eraseFromParent();
RecursivelyDeleteTriviallyDeadInstructions(Cond);
Changed = true;
}
if (Changed) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
return PreservedAnalyses::all();
}
|
