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
|
// SPDX-License-Identifier: GPL-3.0-or-later
#include "rcc/CodeGen/MachineShrinkWrapping.h"
#include "rcc/CodeGen/InstructionDescriptor.h"
#include "rcc/CodeGen/MachineAnalyses.h"
#include "rcc/CodeGen/MachineBasicBlock.h"
#include "rcc/CodeGen/MachineFrameInfo.h"
#include "rcc/CodeGen/MachineFunction.h"
#include "rcc/CodeGen/MachineInstr.h"
#include "rcc/CodeGen/MachineMemOperand.h"
#include "rcc/CodeGen/MachineOperand.h"
#include "rcc/CodeGen/TargetDescription.h"
#include "rcc/CodeGen/TargetFrameLowering.h"
#include <algorithm>
#include <cstddef>
#include <optional>
#include <ranges>
#include <unordered_set>
#include <vector>
namespace rcc {
namespace {
[[nodiscard]] const MachinePassContract &shrinkWrappingContract() {
static const MachinePassContract Contract = [] {
MachinePassContract Value{
.Name = "machine-shrink-wrapping",
.Requires = {MachineFunctionProperty::NoVRegs},
.Sets = {},
.Clears = {},
.RequiredAnalyses = {MachineFunctionAnalysisManager::id<MachineDominatorTreeAnalysis>(),
MachineFunctionAnalysisManager::id<MachineLoopAnalysis>()},
.VerificationStage = PipelineStage::RegisterAllocated,
};
Value.ThreadSafety = PassThreadSafety::ThreadSafe;
Value.DeclaredChanges = {MachinePassChange::Frame};
return Value;
}();
return Contract;
}
[[nodiscard]] bool requiresEntryFrame(const MachineFrameState &State) noexcept {
return State.IsFrameAddressTaken || State.IsReturnAddressTaken || State.HasStackMap ||
State.HasPatchPoint || State.HasOpaqueSPAdjustment || State.HasVAStart ||
State.HasMustTailInVarArgFunc || State.HasTailCall;
}
[[nodiscard]] bool containsEpilogueTerminator(const MachineBasicBlock &Block,
const TargetFrameLowering &Info,
const TargetDescription &Target) noexcept {
for (const MachineInstr *Instruction = Block.firstInstruction(); Instruction != nullptr;
Instruction = Instruction->next()) {
if (Info.isEpilogueTerminator(*Instruction, Target))
return true;
}
return false;
}
} // namespace
const MachinePassContract &MachineShrinkWrappingPass::contract() const noexcept {
return shrinkWrappingContract();
}
Expected<MachinePassResult>
MachineShrinkWrappingPass::run(MachineFunction &Function, const TargetDescription &Target,
MachineFunctionAnalysisManager &Analyses) {
if (Function.frameInfo().isFrozen()) {
return makeUnexpected(ErrorCode::FrameLayoutFailed,
"shrink wrapping must run before frame layout freeze");
}
if (Function.blockCount() > Options.MaximumAnalyzedBlocks) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
const MachineFrameState &OriginalState = Function.frameInfo().state();
if (!OriginalState.SavePoints.empty() || !OriginalState.RestorePoints.empty()) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
MachineBasicBlock *Entry = Function.firstBlock();
if (Entry == nullptr || requiresEntryFrame(OriginalState)) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
auto Dominators = Analyses.getResult<MachineDominatorTreeAnalysis>(Function, Target);
if (!Dominators)
return std::unexpected(Dominators.error());
auto Loops = Analyses.getResult<MachineLoopAnalysis>(Function, Target);
if (!Loops)
return std::unexpected(Loops.error());
std::vector<MachineBasicBlock *> RequiredBlocks;
std::unordered_set<FrameIndex> ReferencedObjects;
for (MachineBasicBlock *Block = Function.firstBlock(); Block != nullptr; Block = Block->next()) {
bool Required = false;
for (const MachineInstr *Instruction = Block->firstInstruction(); Instruction != nullptr;
Instruction = Instruction->next()) {
const InstructionDescriptor *Descriptor = Target.instructionDescriptor(Instruction->opcode());
if (Descriptor == nullptr) {
return makeUnexpected(ErrorCode::VerificationError,
"shrink wrapping encountered an unknown opcode");
}
Required |= Descriptor->Flags.has(InstructionFlag::Call);
for (const MachineOperand &Operand : Instruction->operands()) {
if (const auto *Frame = Operand.getIf<FrameIndexOperand>()) {
ReferencedObjects.insert(Frame->Index);
Required = true;
}
const Register *Reg = Operand.getIf<Register>();
const std::optional<PhysicalRegister> Physical =
Reg == nullptr ? std::nullopt : Reg->physicalRegister();
if (Physical && Operand.isDef() &&
Info->isCalleeSavedRegister(*Physical, Function, Target)) {
Required = true;
}
}
for (const MachineMemOperand *Memory : Instruction->memOperands()) {
const std::optional<FrameIndex> Frame =
Memory == nullptr ? std::nullopt : Memory->description().Base.frameIndex();
if (Frame) {
ReferencedObjects.insert(*Frame);
Required = true;
}
}
}
if (Required)
RequiredBlocks.push_back(Block);
}
for (const StackObject &Object : Function.frameInfo().objects()) {
const StackObjectDesc *Description = Object.description();
if (Description == nullptr || Description->IsDead)
continue;
if (!ReferencedObjects.contains(Object.index())) {
RequiredBlocks.push_back(Entry);
break;
}
}
if (RequiredBlocks.empty()) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
const MachineBasicBlock *Save = RequiredBlocks.front();
if (!(*Dominators)->isReachable(*Save))
Save = Entry;
for (MachineBasicBlock *Block : RequiredBlocks) {
if (!(*Dominators)->isReachable(*Block)) {
Save = Entry;
break;
}
const MachineBasicBlock *Common = (*Dominators)->nearestCommonDominator(*Save, *Block);
if (Common == nullptr) {
Save = Entry;
break;
}
Save = Common;
}
if (Save == Entry || Save->predecessors().size() != 1 || (*Loops)->loopDepth(*Save) != 0 ||
(*Loops)->isIrreducible(*Save)) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
std::vector<MachineBasicBlock *> RestoreBlocks;
for (MachineBasicBlock *Block = Function.firstBlock(); Block != nullptr; Block = Block->next()) {
if (!(*Dominators)->dominates(*Save, *Block))
continue;
for (const MachineSuccessor &Successor : Block->successors()) {
if (Successor.Block == nullptr || !(*Dominators)->dominates(*Save, *Successor.Block)) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
}
if (!Block->successors().empty())
continue;
if (!containsEpilogueTerminator(*Block, *Info, Target)) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
RestoreBlocks.push_back(Block);
}
if (RestoreBlocks.empty()) {
MachinePassResult Result;
Result.Preserved = PreservedAnalyses::all();
return Result;
}
MachineFrameState Planned = OriginalState;
Planned.SavePoints.push_back({Save->stableID(), {}});
std::ranges::sort(RestoreBlocks, {},
[](const MachineBasicBlock *Block) { return Block->stableID().value(); });
for (const MachineBasicBlock *Block : RestoreBlocks)
Planned.RestorePoints.push_back({Block->stableID(), {}});
auto Updated = Function.frameInfo().setState(std::move(Planned));
if (!Updated)
return std::unexpected(Updated.error());
MachinePassResult Result;
Result.Changed = true;
Result.Changes = {MachinePassChange::Frame};
Result.Preserved.preserve<MachineDominatorTreeAnalysis>();
Result.Preserved.preserve<MachineLoopAnalysis>();
Result.Preserved.preserve<MachineBranchProbabilityAnalysis>();
Result.Preserved.preserve<MachineBlockFrequencyAnalysis>();
return Result;
}
} // namespace rcc
|
