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llvm-6502/lib/CodeGen/UnreachableBlockElim.cpp
Chandler Carruth 0b8c9a80f2 Move all of the header files which are involved in modelling the LLVM IR
into their new header subdirectory: include/llvm/IR. This matches the
directory structure of lib, and begins to correct a long standing point
of file layout clutter in LLVM.

There are still more header files to move here, but I wanted to handle
them in separate commits to make tracking what files make sense at each
layer easier.

The only really questionable files here are the target intrinsic
tablegen files. But that's a battle I'd rather not fight today.

I've updated both CMake and Makefile build systems (I think, and my
tests think, but I may have missed something).

I've also re-sorted the includes throughout the project. I'll be
committing updates to Clang, DragonEgg, and Polly momentarily.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171366 91177308-0d34-0410-b5e6-96231b3b80d8
2013-01-02 11:36:10 +00:00

216 lines
7.3 KiB
C++

//===-- 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/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
namespace {
class UnreachableBlockElim : public FunctionPass {
virtual bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
UnreachableBlockElim() : FunctionPass(ID) {
initializeUnreachableBlockElimPass(*PassRegistry::getPassRegistry());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<DominatorTree>();
AU.addPreserved<ProfileInfo>();
}
};
}
char UnreachableBlockElim::ID = 0;
INITIALIZE_PASS(UnreachableBlockElim, "unreachableblockelim",
"Remove unreachable blocks from the CFG", false, false)
FunctionPass *llvm::createUnreachableBlockEliminationPass() {
return new UnreachableBlockElim();
}
bool UnreachableBlockElim::runOnFunction(Function &F) {
SmallPtrSet<BasicBlock*, 8> Reachable;
// Mark all reachable blocks.
for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > 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.
ProfileInfo *PI = getAnalysisIfAvailable<ProfileInfo>();
for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
if (PI) PI->removeBlock(DeadBlocks[i]);
DeadBlocks[i]->eraseFromParent();
}
return DeadBlocks.size();
}
namespace {
class UnreachableMachineBlockElim : public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
MachineModuleInfo *MMI;
public:
static char ID; // Pass identification, replacement for typeid
UnreachableMachineBlockElim() : MachineFunctionPass(ID) {}
};
}
char UnreachableMachineBlockElim::ID = 0;
INITIALIZE_PASS(UnreachableMachineBlockElim, "unreachable-mbb-elimination",
"Remove unreachable machine basic blocks", false, false)
char &llvm::UnreachableMachineBlockElimID = UnreachableMachineBlockElim::ID;
void UnreachableMachineBlockElim::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
SmallPtrSet<MachineBasicBlock*, 8> Reachable;
bool ModifiedPHI = false;
MMI = getAnalysisIfAvailable<MachineModuleInfo>();
MachineDominatorTree *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
MachineLoopInfo *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
// Mark all reachable blocks.
for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
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) {
MachineBasicBlock *BB = I;
// Test for deadness.
if (!Reachable.count(BB)) {
DeadBlocks.push_back(BB);
// Update dominator and loop info.
if (MLI) MLI->removeBlock(BB);
if (MDT && MDT->getNode(BB)) MDT->eraseNode(BB);
while (BB->succ_begin() != BB->succ_end()) {
MachineBasicBlock* succ = *BB->succ_begin();
MachineBasicBlock::iterator start = succ->begin();
while (start != succ->end() && start->isPHI()) {
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);
}
start++;
}
BB->removeSuccessor(BB->succ_begin());
}
}
}
// Actually remove the blocks now.
for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
DeadBlocks[i]->eraseFromParent();
// Cleanup PHI nodes.
for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
MachineBasicBlock *BB = I;
// Prune unneeded PHI entries.
SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
BB->pred_end());
MachineBasicBlock::iterator phi = BB->begin();
while (phi != BB->end() && phi->isPHI()) {
for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
if (!preds.count(phi->getOperand(i).getMBB())) {
phi->RemoveOperand(i);
phi->RemoveOperand(i-1);
ModifiedPHI = true;
}
if (phi->getNumOperands() == 3) {
unsigned Input = phi->getOperand(1).getReg();
unsigned Output = phi->getOperand(0).getReg();
MachineInstr* temp = phi;
++phi;
temp->eraseFromParent();
ModifiedPHI = true;
if (Input != Output) {
MachineRegisterInfo &MRI = F.getRegInfo();
MRI.constrainRegClass(Input, MRI.getRegClass(Output));
MRI.replaceRegWith(Output, Input);
}
continue;
}
++phi;
}
}
F.RenumberBlocks();
return (DeadBlocks.size() || ModifiedPHI);
}