LLVM 19.0.0git
FlattenCFGPass.cpp
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1//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements flattening of CFG.
10//
11//===----------------------------------------------------------------------===//
12
14#include "llvm/IR/PassManager.h"
15#include "llvm/IR/ValueHandle.h"
17#include "llvm/Pass.h"
21
22using namespace llvm;
23
24#define DEBUG_TYPE "flatten-cfg"
25
26namespace {
27struct FlattenCFGLegacyPass : public FunctionPass {
28 static char ID; // Pass identification, replacement for typeid
29public:
30 FlattenCFGLegacyPass() : FunctionPass(ID) {
32 }
33 bool runOnFunction(Function &F) override;
34
35 void getAnalysisUsage(AnalysisUsage &AU) const override {
37 }
38
39private:
40 AliasAnalysis *AA;
41};
42
43/// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function,
44/// iterating until no more changes are made.
45bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) {
46 bool Changed = false;
47 bool LocalChange = true;
48
49 // Use block handles instead of iterating over function blocks directly
50 // to avoid using iterators invalidated by erasing blocks.
51 std::vector<WeakVH> Blocks;
52 Blocks.reserve(F.size());
53 for (auto &BB : F)
54 Blocks.push_back(&BB);
55
56 while (LocalChange) {
57 LocalChange = false;
58
59 // Loop over all of the basic blocks and try to flatten them.
60 for (WeakVH &BlockHandle : Blocks) {
61 // Skip blocks erased by FlattenCFG.
62 if (auto *BB = cast_or_null<BasicBlock>(BlockHandle))
63 if (FlattenCFG(BB, AA))
64 LocalChange = true;
65 }
66 Changed |= LocalChange;
67 }
68 return Changed;
69}
70} // namespace
71
72char FlattenCFGLegacyPass::ID = 0;
73
74INITIALIZE_PASS_BEGIN(FlattenCFGLegacyPass, "flattencfg", "Flatten the CFG",
75 false, false)
77INITIALIZE_PASS_END(FlattenCFGLegacyPass, "flattencfg", "Flatten the CFG",
79
80// Public interface to the FlattenCFG pass
82 return new FlattenCFGLegacyPass();
83}
84
85bool FlattenCFGLegacyPass::runOnFunction(Function &F) {
86 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
87 bool EverChanged = false;
88 // iterativelyFlattenCFG can make some blocks dead.
89 while (iterativelyFlattenCFG(F, AA)) {
91 EverChanged = true;
92 }
93 return EverChanged;
94}
95
98 bool EverChanged = false;
100 // iterativelyFlattenCFG can make some blocks dead.
101 while (iterativelyFlattenCFG(F, AA)) {
103 EverChanged = true;
104 }
105 return EverChanged ? PreservedAnalyses::none() : PreservedAnalyses::all();
106}
DenseMap< Block *, BlockRelaxAux > Blocks
Definition: ELF_riscv.cpp:507
Flatten the CFG
flattencfg
#define F(x, y, z)
Definition: MD5.cpp:55
This header defines various interfaces for pass management in LLVM.
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:55
#define INITIALIZE_PASS_END(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:59
#define INITIALIZE_PASS_BEGIN(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:52
A manager for alias analyses.
A wrapper pass to provide the legacy pass manager access to a suitably prepared AAResults object.
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:500
Represent the analysis usage information of a pass.
AnalysisUsage & addRequired()
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:311
virtual bool runOnFunction(Function &F)=0
runOnFunction - Virtual method overriden by subclasses to do the per-function processing of the pass.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
virtual void getAnalysisUsage(AnalysisUsage &) const
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
Definition: Pass.cpp:98
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
static PreservedAnalyses none()
Convenience factory function for the empty preserved set.
Definition: Analysis.h:112
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:115
A nullable Value handle that is nullable.
Definition: ValueHandle.h:144
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
FunctionPass * createFlattenCFGPass()
bool FlattenCFG(BasicBlock *BB, AAResults *AA=nullptr)
This function is used to flatten a CFG.
Definition: FlattenCFG.cpp:533
void initializeFlattenCFGLegacyPassPass(PassRegistry &)
bool removeUnreachableBlocks(Function &F, DomTreeUpdater *DTU=nullptr, MemorySSAUpdater *MSSAU=nullptr)
Remove all blocks that can not be reached from the function's entry.
Definition: Local.cpp:3162
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)