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//===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass is an extremely simple version of the SimplifyCFG pass. Its sole
// job is to delete LLVM basic blocks that are not reachable from the entry
// node. To do this, it performs a simple depth first traversal of the CFG,
// then deletes any unvisited nodes.
//
// Note that this pass is really a hack. In particular, the instruction
// selectors for various targets should just not generate code for unreachable
// blocks. Until LLVM has a more systematic way of defining instruction
// selectors, however, we cannot really expect them to handle additional
// complexity.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/Constant.h"
#include "llvm/Instructions.h"
#include "llvm/Function.h"
#include "llvm/Pass.h"
#include "llvm/Type.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/ADT/DepthFirstIterator.h"
using namespace llvm;
namespace {
class VISIBILITY_HIDDEN UnreachableBlockElim : public FunctionPass {
virtual bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
UnreachableBlockElim() : FunctionPass((intptr_t)&ID) {}
};
}
char UnreachableBlockElim::ID = 0;
static RegisterPass<UnreachableBlockElim>
X("unreachableblockelim", "Remove unreachable blocks from the CFG");
FunctionPass *llvm::createUnreachableBlockEliminationPass() {
return new UnreachableBlockElim();
}
bool UnreachableBlockElim::runOnFunction(Function &F) {
std::set<BasicBlock*> Reachable;
// Mark all reachable blocks.
for (df_ext_iterator<Function*> I = df_ext_begin(&F, Reachable),
E = df_ext_end(&F, Reachable); I != E; ++I)
/* Mark all reachable blocks */;
// Loop over all dead blocks, remembering them and deleting all instructions
// in them.
std::vector<BasicBlock*> DeadBlocks;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (!Reachable.count(I)) {
BasicBlock *BB = I;
DeadBlocks.push_back(BB);
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
BB->getInstList().pop_front();
}
for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
(*SI)->removePredecessor(BB);
BB->dropAllReferences();
}
// Actually remove the blocks now.
for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
DeadBlocks[i]->eraseFromParent();
return DeadBlocks.size();
}
namespace {
class VISIBILITY_HIDDEN UnreachableMachineBlockElim :
public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &F);
public:
static char ID; // Pass identification, replacement for typeid
UnreachableMachineBlockElim() : MachineFunctionPass((intptr_t)&ID) {}
};
}
char UnreachableMachineBlockElim::ID = 0;
static RegisterPass<UnreachableMachineBlockElim>
Y("unreachable-mbb-elimination",
"Remove unreachable machine basic blocks");
const PassInfo *const llvm::UnreachableMachineBlockElimID = &Y;
bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
std::set<MachineBasicBlock*> Reachable;
// Mark all reachable blocks.
for (df_ext_iterator<MachineFunction*> I = df_ext_begin(&F, Reachable),
E = df_ext_end(&F, Reachable); I != E; ++I)
/* Mark all reachable blocks */;
// Loop over all dead blocks, remembering them and deleting all instructions
// in them.
std::vector<MachineBasicBlock*> DeadBlocks;
for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (!Reachable.count(I)) {
MachineBasicBlock *BB = I;
DeadBlocks.push_back(BB);
while (BB->succ_begin() != BB->succ_end()) {
MachineBasicBlock* succ = *BB->succ_begin();
MachineBasicBlock::iterator start = succ->begin();
while (start != succ->end() &&
start->getOpcode() == TargetInstrInfo::PHI) {
for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
if (start->getOperand(i).isMBB() &&
start->getOperand(i).getMBB() == BB) {
start->RemoveOperand(i);
start->RemoveOperand(i-1);
}
if (start->getNumOperands() == 3) {
MachineInstr* phi = start;
unsigned Input = phi->getOperand(1).getReg();
unsigned Output = phi->getOperand(0).getReg();
start++;
phi->eraseFromParent();
if (Input != Output)
F.getRegInfo().replaceRegWith(Output, Input);
} else
start++;
}
BB->removeSuccessor(BB->succ_begin());
}
}
// Actually remove the blocks now.
for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
DeadBlocks[i]->eraseFromParent();
F.RenumberBlocks();
return DeadBlocks.size();
}
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