Quotes should be printed before private prefix; some code clean up.
[llvm/msp430.git] / lib / CodeGen / UnreachableBlockElim.cpp
blobc3b213cebe9543a95020d13b26a95c215e91661d
1 //===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass is an extremely simple version of the SimplifyCFG pass. Its sole
11 // job is to delete LLVM basic blocks that are not reachable from the entry
12 // node. To do this, it performs a simple depth first traversal of the CFG,
13 // then deletes any unvisited nodes.
15 // Note that this pass is really a hack. In particular, the instruction
16 // selectors for various targets should just not generate code for unreachable
17 // blocks. Until LLVM has a more systematic way of defining instruction
18 // selectors, however, we cannot really expect them to handle additional
19 // complexity.
21 //===----------------------------------------------------------------------===//
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/Constant.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/Function.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Type.h"
29 #include "llvm/CodeGen/MachineFunctionPass.h"
30 #include "llvm/CodeGen/MachineModuleInfo.h"
31 #include "llvm/CodeGen/MachineRegisterInfo.h"
32 #include "llvm/Support/CFG.h"
33 #include "llvm/Support/Compiler.h"
34 #include "llvm/Target/TargetInstrInfo.h"
35 #include "llvm/ADT/DepthFirstIterator.h"
36 #include "llvm/ADT/SmallPtrSet.h"
37 using namespace llvm;
39 namespace {
40 class VISIBILITY_HIDDEN UnreachableBlockElim : public FunctionPass {
41 virtual bool runOnFunction(Function &F);
42 public:
43 static char ID; // Pass identification, replacement for typeid
44 UnreachableBlockElim() : FunctionPass(&ID) {}
47 char UnreachableBlockElim::ID = 0;
48 static RegisterPass<UnreachableBlockElim>
49 X("unreachableblockelim", "Remove unreachable blocks from the CFG");
51 FunctionPass *llvm::createUnreachableBlockEliminationPass() {
52 return new UnreachableBlockElim();
55 bool UnreachableBlockElim::runOnFunction(Function &F) {
56 SmallPtrSet<BasicBlock*, 8> Reachable;
58 // Mark all reachable blocks.
59 for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > I =
60 df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); I != E; ++I)
61 /* Mark all reachable blocks */;
63 // Loop over all dead blocks, remembering them and deleting all instructions
64 // in them.
65 std::vector<BasicBlock*> DeadBlocks;
66 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
67 if (!Reachable.count(I)) {
68 BasicBlock *BB = I;
69 DeadBlocks.push_back(BB);
70 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
71 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
72 BB->getInstList().pop_front();
74 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
75 (*SI)->removePredecessor(BB);
76 BB->dropAllReferences();
79 // Actually remove the blocks now.
80 for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
81 DeadBlocks[i]->eraseFromParent();
83 return DeadBlocks.size();
87 namespace {
88 class VISIBILITY_HIDDEN UnreachableMachineBlockElim :
89 public MachineFunctionPass {
90 virtual bool runOnMachineFunction(MachineFunction &F);
91 MachineModuleInfo *MMI;
92 public:
93 static char ID; // Pass identification, replacement for typeid
94 UnreachableMachineBlockElim() : MachineFunctionPass(&ID) {}
97 char UnreachableMachineBlockElim::ID = 0;
99 static RegisterPass<UnreachableMachineBlockElim>
100 Y("unreachable-mbb-elimination",
101 "Remove unreachable machine basic blocks");
103 const PassInfo *const llvm::UnreachableMachineBlockElimID = &Y;
105 bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
106 SmallPtrSet<MachineBasicBlock*, 8> Reachable;
108 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
110 // Mark all reachable blocks.
111 for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
112 I = df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable);
113 I != E; ++I)
114 /* Mark all reachable blocks */;
116 // Loop over all dead blocks, remembering them and deleting all instructions
117 // in them.
118 std::vector<MachineBasicBlock*> DeadBlocks;
119 for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
120 MachineBasicBlock *BB = I;
122 // Test for deadness.
123 if (!Reachable.count(BB)) {
124 DeadBlocks.push_back(BB);
126 while (BB->succ_begin() != BB->succ_end()) {
127 MachineBasicBlock* succ = *BB->succ_begin();
129 MachineBasicBlock::iterator start = succ->begin();
130 while (start != succ->end() &&
131 start->getOpcode() == TargetInstrInfo::PHI) {
132 for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
133 if (start->getOperand(i).isMBB() &&
134 start->getOperand(i).getMBB() == BB) {
135 start->RemoveOperand(i);
136 start->RemoveOperand(i-1);
139 start++;
142 BB->removeSuccessor(BB->succ_begin());
147 // Actually remove the blocks now.
148 for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
149 MachineBasicBlock *MBB = DeadBlocks[i];
150 // If there are any labels in the basic block, unregister them from
151 // MachineModuleInfo.
152 if (MMI && !MBB->empty()) {
153 for (MachineBasicBlock::iterator I = MBB->begin(),
154 E = MBB->end(); I != E; ++I) {
155 if (I->isLabel())
156 // The label ID # is always operand #0, an immediate.
157 MMI->InvalidateLabel(I->getOperand(0).getImm());
160 MBB->eraseFromParent();
163 // Cleanup PHI nodes.
164 for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
165 MachineBasicBlock *BB = I;
166 // Prune unneeded PHI entries.
167 SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
168 BB->pred_end());
169 MachineBasicBlock::iterator phi = BB->begin();
170 while (phi != BB->end() &&
171 phi->getOpcode() == TargetInstrInfo::PHI) {
172 for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
173 if (!preds.count(phi->getOperand(i).getMBB())) {
174 phi->RemoveOperand(i);
175 phi->RemoveOperand(i-1);
178 if (phi->getNumOperands() == 3) {
179 unsigned Input = phi->getOperand(1).getReg();
180 unsigned Output = phi->getOperand(0).getReg();
182 MachineInstr* temp = phi;
183 ++phi;
184 temp->eraseFromParent();
186 if (Input != Output)
187 F.getRegInfo().replaceRegWith(Output, Input);
189 continue;
192 ++phi;
196 F.RenumberBlocks();
198 return DeadBlocks.size();