//===- ADCE.cpp - Code to perform aggressive dead code elimination --------===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// This file implements "aggressive" dead code elimination. ADCE is DCe where
-// values are assumed to be dead until proven otherwise. This is similar to
+// values are assumed to be dead until proven otherwise. This is similar to
// SCCP, except applied to the liveness of values.
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "adce"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Compiler.h"
#include <algorithm>
using namespace llvm;
-namespace {
- Statistic<> NumBlockRemoved("adce", "Number of basic blocks removed");
- Statistic<> NumInstRemoved ("adce", "Number of instructions removed");
- Statistic<> NumCallRemoved ("adce", "Number of calls and invokes removed");
+STATISTIC(NumBlockRemoved, "Number of basic blocks removed");
+STATISTIC(NumInstRemoved , "Number of instructions removed");
+STATISTIC(NumCallRemoved , "Number of calls removed");
+namespace {
//===----------------------------------------------------------------------===//
// ADCE Class
//
// This class does all of the work of Aggressive Dead Code Elimination.
// It's public interface consists of a constructor and a doADCE() method.
//
-class ADCE : public FunctionPass {
+class VISIBILITY_HIDDEN ADCE : public FunctionPass {
Function *Func; // The function that we are working on
std::vector<Instruction*> WorkList; // Instructions that just became live
std::set<Instruction*> LiveSet; // The set of live instructions
// The public interface for this class
//
public:
+ static char ID; // Pass identification, replacement for typeid
+ ADCE() : FunctionPass((intptr_t)&ID) {}
+
// Execute the Aggressive Dead Code Elimination Algorithm
//
virtual bool runOnFunction(Function &F) {
inline void markInstructionLive(Instruction *I) {
if (!LiveSet.insert(I).second) return;
- DEBUG(std::cerr << "Insn Live: " << *I);
+ DOUT << "Insn Live: " << *I;
WorkList.push_back(I);
}
inline void markTerminatorLive(const BasicBlock *BB) {
- DEBUG(std::cerr << "Terminator Live: " << *BB->getTerminator());
+ DOUT << "Terminator Live: " << *BB->getTerminator();
markInstructionLive(const_cast<TerminatorInst*>(BB->getTerminator()));
}
};
- RegisterOpt<ADCE> X("adce", "Aggressive Dead Code Elimination");
+ char ADCE::ID = 0;
+ RegisterPass<ADCE> X("adce", "Aggressive Dead Code Elimination");
} // End of anonymous namespace
FunctionPass *llvm::createAggressiveDCEPass() { return new ADCE(); }
if (It != CDG.end()) {
// Get the blocks that this node is control dependent on...
const PostDominanceFrontier::DomSetType &CDB = It->second;
- for_each(CDB.begin(), CDB.end(), // Mark all their terminators as live
- bind_obj(this, &ADCE::markTerminatorLive));
+ for (PostDominanceFrontier::DomSetType::const_iterator I =
+ CDB.begin(), E = CDB.end(); I != E; ++I)
+ markTerminatorLive(*I); // Mark all their terminators as live
}
-
+
// If this basic block is live, and it ends in an unconditional branch, then
// the branch is alive as well...
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
/// successors it goes to. This eliminate a use of the condition as well.
///
TerminatorInst *ADCE::convertToUnconditionalBranch(TerminatorInst *TI) {
- BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI);
+ BranchInst *NB = BranchInst::Create(TI->getSuccessor(0), TI);
BasicBlock *BB = TI->getParent();
// Remove entries from PHI nodes to avoid confusing ourself later...
for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
TI->getSuccessor(i)->removePredecessor(BB);
-
+
// Delete the old branch itself...
BB->getInstList().erase(TI);
return NB;
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
- // Iterate over all invokes in the function, turning invokes into calls if
- // they cannot throw.
- for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB)
- if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
- if (Function *F = II->getCalledFunction())
- if (AA.onlyReadsMemory(F)) {
- // The function cannot unwind. Convert it to a call with a branch
- // after it to the normal destination.
- std::vector<Value*> Args(II->op_begin()+3, II->op_end());
- std::string Name = II->getName(); II->setName("");
- Instruction *NewCall = new CallInst(F, Args, Name, II);
- II->replaceAllUsesWith(NewCall);
- new BranchInst(II->getNormalDest(), II);
-
- // Update PHI nodes in the unwind destination
- II->getUnwindDest()->removePredecessor(BB);
- BB->getInstList().erase(II);
-
- if (NewCall->use_empty()) {
- BB->getInstList().erase(NewCall);
- ++NumCallRemoved;
- }
- }
-
// Iterate over all of the instructions in the function, eliminating trivially
- // dead instructions, and marking instructions live that are known to be
+ // dead instructions, and marking instructions live that are known to be
// needed. Perform the walk in depth first order so that we avoid marking any
// instructions live in basic blocks that are unreachable. These blocks will
// be eliminated later, along with the instructions inside.
for (BasicBlock::iterator II = BB->begin(), EI = BB->end(); II != EI; ) {
Instruction *I = II++;
if (CallInst *CI = dyn_cast<CallInst>(I)) {
- Function *F = CI->getCalledFunction();
- if (F && AA.onlyReadsMemory(F)) {
+ if (AA.onlyReadsMemory(CI)) {
if (CI->use_empty()) {
BB->getInstList().erase(CI);
++NumCallRemoved;
isa<UnwindInst>(I) || isa<UnreachableInst>(I)) {
// FIXME: Unreachable instructions should not be marked intrinsically
// live here.
- markInstructionLive(I);
+ markInstructionLive(I);
} else if (isInstructionTriviallyDead(I)) {
// Remove the instruction from it's basic block...
BB->getInstList().erase(I);
// function which unwinds, exits or has side-effects, we don't want to delete
// the infinite loop or those blocks leading up to it.
for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
- if (DT[I] == 0)
+ if (DT[I] == 0 && ReachableBBs.count(I))
for (pred_iterator PI = pred_begin(I), E = pred_end(I); PI != E; ++PI)
markInstructionLive((*PI)->getTerminator());
- DEBUG(std::cerr << "Processing work list\n");
+ DOUT << "Processing work list\n";
// AliveBlocks - Set of basic blocks that we know have instructions that are
// alive in them...
// defined in the predecessor nodes of this block, meaning that the PHI
// makes the predecessors alive.
//
- if (PHINode *PN = dyn_cast<PHINode>(I))
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- if (AliveBlocks.insert(PN->getIncomingBlock(i)).second)
- markBlockAlive(PN->getIncomingBlock(i)); // Block is newly ALIVE!
-
- // Loop over all of the operands of the live instruction, making sure that
- // they are known to be alive as well.
- //
- for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
- if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
- markInstructionLive(Operand);
+ if (PHINode *PN = dyn_cast<PHINode>(I)) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ // If the incoming edge is clearly dead, it won't have control
+ // dependence information. Do not mark it live.
+ BasicBlock *PredBB = PN->getIncomingBlock(i);
+ if (ReachableBBs.count(PredBB)) {
+ // FIXME: This should mark the control dependent edge as live, not
+ // necessarily the predecessor itself!
+ if (AliveBlocks.insert(PredBB).second)
+ markBlockAlive(PN->getIncomingBlock(i)); // Block is newly ALIVE!
+ if (Instruction *Op = dyn_cast<Instruction>(PN->getIncomingValue(i)))
+ markInstructionLive(Op);
+ }
+ }
+ } else {
+ // Loop over all of the operands of the live instruction, making sure that
+ // they are known to be alive as well.
+ //
+ for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
+ if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
+ markInstructionLive(Operand);
+ }
}
DEBUG(
- std::cerr << "Current Function: X = Live\n";
+ DOUT << "Current Function: X = Live\n";
for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I){
- std::cerr << I->getName() << ":\t"
- << (AliveBlocks.count(I) ? "LIVE\n" : "DEAD\n");
+ DOUT << I->getName() << ":\t"
+ << (AliveBlocks.count(I) ? "LIVE\n" : "DEAD\n");
for (BasicBlock::iterator BI = I->begin(), BE = I->end(); BI != BE; ++BI){
- if (LiveSet.count(BI)) std::cerr << "X ";
- std::cerr << *BI;
+ if (LiveSet.count(BI)) DOUT << "X ";
+ DOUT << *BI;
}
});
return MadeChanges;
}
-
+
// If the entry node is dead, insert a new entry node to eliminate the entry
// node as a special case.
//
if (!AliveBlocks.count(&Func->front())) {
- BasicBlock *NewEntry = new BasicBlock();
- new BranchInst(&Func->front(), NewEntry);
+ BasicBlock *NewEntry = BasicBlock::Create();
+ BranchInst::Create(&Func->front(), NewEntry);
Func->getBasicBlockList().push_front(NewEntry);
AliveBlocks.insert(NewEntry); // This block is always alive!
LiveSet.insert(NewEntry->getTerminator()); // The branch is live
}
-
+
// Loop over all of the alive blocks in the function. If any successor
// blocks are not alive, we adjust the outgoing branches to branch to the
// first live postdominator of the live block, adjusting any PHI nodes in
if (AliveBlocks.count(I)) {
BasicBlock *BB = I;
TerminatorInst *TI = BB->getTerminator();
-
+
// If the terminator instruction is alive, but the block it is contained
// in IS alive, this means that this terminator is a conditional branch on
// a condition that doesn't matter. Make it an unconditional branch to
// Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction
- // here because we may remove them if we don't have a postdominator...
+ // here because we may remove them if we don't have a postdominator.
//
for (unsigned i = 0; i != TI->getNumSuccessors(); ++i)
if (!AliveBlocks.count(TI->getSuccessor(i))) {
// postdominator that is alive, and the last postdominator that is
// dead...
//
- PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)];
+ DomTreeNode *LastNode = DT[TI->getSuccessor(i)];
+ DomTreeNode *NextNode = 0;
+
+ if (LastNode) {
+ NextNode = LastNode->getIDom();
+ while (!AliveBlocks.count(NextNode->getBlock())) {
+ LastNode = NextNode;
+ NextNode = NextNode->getIDom();
+ if (NextNode == 0) {
+ LastNode = 0;
+ break;
+ }
+ }
+ }
// There is a special case here... if there IS no post-dominator for
- // the block we have no owhere to point our branch to. Instead,
- // convert it to a return. This can only happen if the code branched
- // into an infinite loop. Note that this may not be desirable,
- // because we _are_ altering the behavior of the code. This is a well
- // known drawback of ADCE, so in the future if we choose to revisit
- // the decision, this is where it should be.
+ // the block we have nowhere to point our branch to. Instead, convert
+ // it to a return. This can only happen if the code branched into an
+ // infinite loop. Note that this may not be desirable, because we
+ // _are_ altering the behavior of the code. This is a well known
+ // drawback of ADCE, so in the future if we choose to revisit the
+ // decision, this is where it should be.
//
if (LastNode == 0) { // No postdominator!
- // Call RemoveSuccessor to transmogrify the terminator instruction
- // to not contain the outgoing branch, or to create a new terminator
- // if the form fundamentally changes (i.e., unconditional branch to
- // return). Note that this will change a branch into an infinite
- // loop into a return instruction!
- //
- RemoveSuccessor(TI, i);
+ if (!isa<InvokeInst>(TI)) {
+ // Call RemoveSuccessor to transmogrify the terminator instruction
+ // to not contain the outgoing branch, or to create a new
+ // terminator if the form fundamentally changes (i.e.,
+ // unconditional branch to return). Note that this will change a
+ // branch into an infinite loop into a return instruction!
+ //
+ RemoveSuccessor(TI, i);
+
+ // RemoveSuccessor may replace TI... make sure we have a fresh
+ // pointer.
+ //
+ TI = BB->getTerminator();
+
+ // Rescan this successor...
+ --i;
+ } else {
- // RemoveSuccessor may replace TI... make sure we have a fresh
- // pointer... and e variable.
- //
- TI = BB->getTerminator();
-
- // Rescan this successor...
- --i;
- } else {
- PostDominatorTree::Node *NextNode = LastNode->getIDom();
-
- while (!AliveBlocks.count(NextNode->getBlock())) {
- LastNode = NextNode;
- NextNode = NextNode->getIDom();
}
-
+ } else {
// Get the basic blocks that we need...
BasicBlock *LastDead = LastNode->getBlock();
BasicBlock *NextAlive = NextNode->getBlock();
int OldIdx = PN->getBasicBlockIndex(LastDead);
assert(OldIdx != -1 &&"LastDead is not a pred of NextAlive!");
Value *InVal = PN->getIncomingValue(OldIdx);
-
+
// Add an incoming value for BB now...
PN->addIncoming(InVal, BB);
}
projects / oota-llvm.git / blobdiff