//===- TailRecursionElimination.cpp - Eliminate Tail Calls ----------------===//
-//
+//
// 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 transforms calls of the current function (self recursion) followed
// transformation from taking place, though currently the analysis cannot
// support moving any really useful instructions (only dead ones).
// 2. This pass transforms functions that are prevented from being tail
-// recursive by an associative expression to use an accumulator variable,
-// thus compiling the typical naive factorial or 'fib' implementation into
-// efficient code.
+// recursive by an associative and commutative expression to use an
+// accumulator variable, thus compiling the typical naive factorial or
+// 'fib' implementation into efficient code.
// 3. TRE is performed if the function returns void, if the return
// returns the result returned by the call, or if the function returns a
// run-time constant on all exits from the function. It is possible, though
// unlikely, that the return returns something else (like constant 0), and
// can still be TRE'd. It can be TRE'd if ALL OTHER return instructions in
// the function return the exact same value.
+// 4. If it can prove that callees do not access their caller stack frame,
+// they are marked as eligible for tail call elimination (by the code
+// generator).
//
// There are several improvements that could be made:
//
// evaluated each time through the tail recursion. Safely keeping allocas
// in the entry block requires analysis to proves that the tail-called
// function does not read or write the stack object.
-// 2. Tail recursion is only performed if the call immediately preceeds the
+// 2. Tail recursion is only performed if the call immediately precedes the
// return instruction. It's possible that there could be a jump between
// the call and the return.
// 3. There can be intervening operations between the call and the return that
// requires some substantial analysis (such as with DSA) to prove safe to
// move ahead of the call, but doing so could allow many more TREs to be
// performed, for example in TreeAdd/TreeAlloc from the treeadd benchmark.
+// 4. The algorithm we use to detect if callees access their caller stack
+// frames is very primitive.
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "tailcallelim"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/InlineCost.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
-#include "Support/Statistic.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ValueHandle.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
-namespace {
- Statistic<> NumEliminated("tailcallelim", "Number of tail calls removed");
- Statistic<> NumAccumAdded("tailcallelim","Number of accumulators introduced");
+STATISTIC(NumEliminated, "Number of tail calls removed");
+STATISTIC(NumRetDuped, "Number of return duplicated");
+STATISTIC(NumAccumAdded, "Number of accumulators introduced");
+namespace {
struct TailCallElim : public FunctionPass {
+ const TargetTransformInfo *TTI;
+
+ static char ID; // Pass identification, replacement for typeid
+ TailCallElim() : FunctionPass(ID) {
+ initializeTailCallElimPass(*PassRegistry::getPassRegistry());
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+
virtual bool runOnFunction(Function &F);
private:
+ CallInst *FindTRECandidate(Instruction *I,
+ bool CannotTailCallElimCallsMarkedTail);
+ bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
+ BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail);
+ bool FoldReturnAndProcessPred(BasicBlock *BB,
+ ReturnInst *Ret, BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail);
bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry,
- std::vector<PHINode*> &ArgumentPHIs);
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail);
bool CanMoveAboveCall(Instruction *I, CallInst *CI);
Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI);
};
- RegisterOpt<TailCallElim> X("tailcallelim", "Tail Call Elimination");
}
+char TailCallElim::ID = 0;
+INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim",
+ "Tail Call Elimination", false, false)
+INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_END(TailCallElim, "tailcallelim",
+ "Tail Call Elimination", false, false)
+
// Public interface to the TailCallElimination pass
FunctionPass *llvm::createTailCallEliminationPass() {
return new TailCallElim();
}
+void TailCallElim::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<TargetTransformInfo>();
+}
+
+/// CanTRE - Scan the specified basic block for alloca instructions.
+/// If it contains any that are variable-sized or not in the entry block,
+/// returns false.
+static bool CanTRE(AllocaInst *AI) {
+ // Because of PR962, we don't TRE allocas outside the entry block.
+
+ // If this alloca is in the body of the function, or if it is a variable
+ // sized allocation, we cannot tail call eliminate calls marked 'tail'
+ // with this mechanism.
+ BasicBlock *BB = AI->getParent();
+ return BB == &BB->getParent()->getEntryBlock() &&
+ isa<ConstantInt>(AI->getArraySize());
+}
+
+namespace {
+struct AllocaCaptureTracker : public CaptureTracker {
+ AllocaCaptureTracker() : Captured(false) {}
+
+ void tooManyUses() LLVM_OVERRIDE { Captured = true; }
+
+ bool shouldExplore(Use *U) LLVM_OVERRIDE {
+ Value *V = U->getUser();
+ if (isa<CallInst>(V) || isa<InvokeInst>(V))
+ UsesAlloca.insert(V);
+ return true;
+ }
+
+ bool captured(Use *U) LLVM_OVERRIDE {
+ if (isa<ReturnInst>(U->getUser()))
+ return false;
+ Captured = true;
+ return true;
+ }
+
+ bool Captured;
+ SmallPtrSet<const Value *, 16> UsesAlloca;
+};
+} // end anonymous namespace
bool TailCallElim::runOnFunction(Function &F) {
+ if (skipOptnoneFunction(F))
+ return false;
+
// If this function is a varargs function, we won't be able to PHI the args
// right, so don't even try to convert it...
if (F.getFunctionType()->isVarArg()) return false;
+ TTI = &getAnalysis<TargetTransformInfo>();
BasicBlock *OldEntry = 0;
- std::vector<PHINode*> ArgumentPHIs;
+ bool TailCallsAreMarkedTail = false;
+ SmallVector<PHINode*, 8> ArgumentPHIs;
bool MadeChange = false;
- // Loop over the function, looking for any returning blocks...
- for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
- if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator()))
- MadeChange |= ProcessReturningBlock(Ret, OldEntry, ArgumentPHIs);
-
+ // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
+ // marked with the 'tail' attribute, because doing so would cause the stack
+ // size to increase (real TRE would deallocate variable sized allocas, TRE
+ // doesn't).
+ bool CanTRETailMarkedCall = true;
+
+ // Find calls that can be marked tail.
+ AllocaCaptureTracker ACT;
+ for (Function::iterator BB = F.begin(), EE = F.end(); BB != EE; ++BB) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
+ CanTRETailMarkedCall &= CanTRE(AI);
+ PointerMayBeCaptured(AI, &ACT);
+ // If any allocas are captured, exit.
+ if (ACT.Captured)
+ return false;
+ }
+ }
+ }
+
+ // Second pass, change any tail recursive calls to loops.
+ //
+ // FIXME: The code generator produces really bad code when an 'escaping
+ // alloca' is changed from being a static alloca to being a dynamic alloca.
+ // Until this is resolved, disable this transformation if that would ever
+ // happen. This bug is PR962.
+ if (ACT.UsesAlloca.empty()) {
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+ if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
+ bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
+ ArgumentPHIs, !CanTRETailMarkedCall);
+ if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
+ Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
+ TailCallsAreMarkedTail, ArgumentPHIs,
+ !CanTRETailMarkedCall);
+ MadeChange |= Change;
+ }
+ }
+ }
+
// If we eliminated any tail recursions, it's possible that we inserted some
// silly PHI nodes which just merge an initial value (the incoming operand)
// with themselves. Check to see if we did and clean up our mess if so. This
// occurs when a function passes an argument straight through to its tail
// call.
if (!ArgumentPHIs.empty()) {
- unsigned NumIncoming = ArgumentPHIs[0]->getNumIncomingValues();
for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) {
PHINode *PN = ArgumentPHIs[i];
- Value *V = 0;
- for (unsigned op = 0, e = NumIncoming; op != e; ++op) {
- Value *Op = PN->getIncomingValue(op);
- if (Op != PN) {
- if (V == 0) {
- V = Op; // First value seen?
- } else if (V != Op) {
- V = 0;
- break;
- }
- }
- }
// If the PHI Node is a dynamic constant, replace it with the value it is.
- if (V) {
- PN->replaceAllUsesWith(V);
- PN->getParent()->getInstList().erase(PN);
+ if (Value *PNV = SimplifyInstruction(PN)) {
+ PN->replaceAllUsesWith(PNV);
+ PN->eraseFromParent();
+ }
+ }
+ }
+
+ // At this point, we know that the function does not have any captured
+ // allocas. If additionally the function does not call setjmp, mark all calls
+ // in the function that do not access stack memory with the tail keyword. This
+ // implies ensuring that there does not exist any path from a call that takes
+ // in an alloca but does not capture it and the call which we wish to mark
+ // with "tail".
+ if (!F.callsFunctionThatReturnsTwice()) {
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ if (CallInst *CI = dyn_cast<CallInst>(I)) {
+ if (!ACT.UsesAlloca.count(CI)) {
+ CI->setTailCall();
+ MadeChange = true;
+ }
+ }
}
}
}
bool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) {
// FIXME: We can move load/store/call/free instructions above the call if the
// call does not mod/ref the memory location being processed.
- if (I->mayWriteToMemory() || isa<LoadInst>(I))
+ if (I->mayHaveSideEffects()) // This also handles volatile loads.
return false;
+ if (LoadInst *L = dyn_cast<LoadInst>(I)) {
+ // Loads may always be moved above calls without side effects.
+ if (CI->mayHaveSideEffects()) {
+ // Non-volatile loads may be moved above a call with side effects if it
+ // does not write to memory and the load provably won't trap.
+ // FIXME: Writes to memory only matter if they may alias the pointer
+ // being loaded from.
+ if (CI->mayWriteToMemory() ||
+ !isSafeToLoadUnconditionally(L->getPointerOperand(), L,
+ L->getAlignment()))
+ return false;
+ }
+ }
+
// Otherwise, if this is a side-effect free instruction, check to make sure
// that it does not use the return value of the call. If it doesn't use the
// return value of the call, it must only use things that are defined before
// We currently handle static constants and arguments that are not modified as
// part of the recursion.
//
-static bool isDynamicConstant(Value *V, CallInst *CI) {
+static bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) {
if (isa<Constant>(V)) return true; // Static constants are always dyn consts
// Check to see if this is an immutable argument, if so, the value
// Figure out which argument number this is...
unsigned ArgNo = 0;
Function *F = CI->getParent()->getParent();
- for (Function::aiterator AI = F->abegin(); &*AI != Arg; ++AI)
+ for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI)
++ArgNo;
-
+
// If we are passing this argument into call as the corresponding
// argument operand, then the argument is dynamically constant.
// Otherwise, we cannot transform this function safely.
- if (CI->getOperand(ArgNo+1) == Arg)
+ if (CI->getArgOperand(ArgNo) == Arg)
return true;
}
+
+ // Switch cases are always constant integers. If the value is being switched
+ // on and the return is only reachable from one of its cases, it's
+ // effectively constant.
+ if (BasicBlock *UniquePred = RI->getParent()->getUniquePredecessor())
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(UniquePred->getTerminator()))
+ if (SI->getCondition() == V)
+ return SI->getDefaultDest() != RI->getParent();
+
// Not a constant or immutable argument, we can't safely transform.
return false;
}
// getCommonReturnValue - Check to see if the function containing the specified
-// return instruction and tail call consistently returns the same
-// runtime-constant value at all exit points. If so, return the returned value.
+// tail call consistently returns the same runtime-constant value at all exit
+// points except for IgnoreRI. If so, return the returned value.
//
-static Value *getCommonReturnValue(ReturnInst *TheRI, CallInst *CI) {
- Function *F = TheRI->getParent()->getParent();
+static Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) {
+ Function *F = CI->getParent()->getParent();
Value *ReturnedValue = 0;
- for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI)
- if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()))
- if (RI != TheRI) {
- Value *RetOp = RI->getOperand(0);
-
- // We can only perform this transformation if the value returned is
- // evaluatable at the start of the initial invocation of the function,
- // instead of at the end of the evaluation.
- //
- if (!isDynamicConstant(RetOp, CI))
- return 0;
-
- if (ReturnedValue && RetOp != ReturnedValue)
- return 0; // Cannot transform if differing values are returned.
- ReturnedValue = RetOp;
- }
+ for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) {
+ ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator());
+ if (RI == 0 || RI == IgnoreRI) continue;
+
+ // We can only perform this transformation if the value returned is
+ // evaluatable at the start of the initial invocation of the function,
+ // instead of at the end of the evaluation.
+ //
+ Value *RetOp = RI->getOperand(0);
+ if (!isDynamicConstant(RetOp, CI, RI))
+ return 0;
+
+ if (ReturnedValue && RetOp != ReturnedValue)
+ return 0; // Cannot transform if differing values are returned.
+ ReturnedValue = RetOp;
+ }
return ReturnedValue;
}
///
Value *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I,
CallInst *CI) {
- if (!I->isAssociative()) return 0;
+ if (!I->isAssociative() || !I->isCommutative()) return 0;
assert(I->getNumOperands() == 2 &&
- "Associative operations should have 2 args!");
+ "Associative/commutative operations should have 2 args!");
- // Exactly one operand should be the result of the call instruction...
- if (I->getOperand(0) == CI && I->getOperand(1) == CI ||
- I->getOperand(0) != CI && I->getOperand(1) != CI)
+ // Exactly one operand should be the result of the call instruction.
+ if ((I->getOperand(0) == CI && I->getOperand(1) == CI) ||
+ (I->getOperand(0) != CI && I->getOperand(1) != CI))
return 0;
// The only user of this instruction we allow is a single return instruction.
return getCommonReturnValue(cast<ReturnInst>(I->use_back()), CI);
}
-bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
- std::vector<PHINode*> &ArgumentPHIs) {
- BasicBlock *BB = Ret->getParent();
+static Instruction *FirstNonDbg(BasicBlock::iterator I) {
+ while (isa<DbgInfoIntrinsic>(I))
+ ++I;
+ return &*I;
+}
+
+CallInst*
+TailCallElim::FindTRECandidate(Instruction *TI,
+ bool CannotTailCallElimCallsMarkedTail) {
+ BasicBlock *BB = TI->getParent();
Function *F = BB->getParent();
- if (&BB->front() == Ret) // Make sure there is something before the ret...
- return false;
+ if (&BB->front() == TI) // Make sure there is something before the terminator.
+ return 0;
// Scan backwards from the return, checking to see if there is a tail call in
// this block. If so, set CI to it.
- CallInst *CI;
- BasicBlock::iterator BBI = Ret;
- while (1) {
+ CallInst *CI = 0;
+ BasicBlock::iterator BBI = TI;
+ while (true) {
CI = dyn_cast<CallInst>(BBI);
if (CI && CI->getCalledFunction() == F)
break;
if (BBI == BB->begin())
- return false; // Didn't find a potential tail call.
+ return 0; // Didn't find a potential tail call.
--BBI;
}
- // If we are introducing accumulator recursion to eliminate associative
- // operations after the call instruction, this variable contains the initial
- // value for the accumulator. If this value is set, we actually perform
- // accumulator recursion elimination instead of simple tail recursion
- // elimination.
+ // If this call is marked as a tail call, and if there are dynamic allocas in
+ // the function, we cannot perform this optimization.
+ if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail)
+ return 0;
+
+ // As a special case, detect code like this:
+ // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
+ // and disable this xform in this case, because the code generator will
+ // lower the call to fabs into inline code.
+ if (BB == &F->getEntryBlock() &&
+ FirstNonDbg(BB->front()) == CI &&
+ FirstNonDbg(llvm::next(BB->begin())) == TI &&
+ CI->getCalledFunction() &&
+ !TTI->isLoweredToCall(CI->getCalledFunction())) {
+ // A single-block function with just a call and a return. Check that
+ // the arguments match.
+ CallSite::arg_iterator I = CallSite(CI).arg_begin(),
+ E = CallSite(CI).arg_end();
+ Function::arg_iterator FI = F->arg_begin(),
+ FE = F->arg_end();
+ for (; I != E && FI != FE; ++I, ++FI)
+ if (*I != &*FI) break;
+ if (I == E && FI == FE)
+ return 0;
+ }
+
+ return CI;
+}
+
+bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
+ BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail) {
+ // If we are introducing accumulator recursion to eliminate operations after
+ // the call instruction that are both associative and commutative, the initial
+ // value for the accumulator is placed in this variable. If this value is set
+ // then we actually perform accumulator recursion elimination instead of
+ // simple tail recursion elimination. If the operation is an LLVM instruction
+ // (eg: "add") then it is recorded in AccumulatorRecursionInstr. If not, then
+ // we are handling the case when the return instruction returns a constant C
+ // which is different to the constant returned by other return instructions
+ // (which is recorded in AccumulatorRecursionEliminationInitVal). This is a
+ // special case of accumulator recursion, the operation being "return C".
Value *AccumulatorRecursionEliminationInitVal = 0;
Instruction *AccumulatorRecursionInstr = 0;
// tail call if all of the instructions between the call and the return are
// movable to above the call itself, leaving the call next to the return.
// Check that this is the case now.
- for (BBI = CI, ++BBI; &*BBI != Ret; ++BBI)
- if (!CanMoveAboveCall(BBI, CI)) {
- // If we can't move the instruction above the call, it might be because it
- // is an associative operation that could be tranformed using accumulator
- // recursion elimination. Check to see if this is the case, and if so,
- // remember the initial accumulator value for later.
- if ((AccumulatorRecursionEliminationInitVal =
- CanTransformAccumulatorRecursion(BBI, CI))) {
- // Yes, this is accumulator recursion. Remember which instruction
- // accumulates.
- AccumulatorRecursionInstr = BBI;
- } else {
- return false; // Otherwise, we cannot eliminate the tail recursion!
- }
+ BasicBlock::iterator BBI = CI;
+ for (++BBI; &*BBI != Ret; ++BBI) {
+ if (CanMoveAboveCall(BBI, CI)) continue;
+
+ // If we can't move the instruction above the call, it might be because it
+ // is an associative and commutative operation that could be transformed
+ // using accumulator recursion elimination. Check to see if this is the
+ // case, and if so, remember the initial accumulator value for later.
+ if ((AccumulatorRecursionEliminationInitVal =
+ CanTransformAccumulatorRecursion(BBI, CI))) {
+ // Yes, this is accumulator recursion. Remember which instruction
+ // accumulates.
+ AccumulatorRecursionInstr = BBI;
+ } else {
+ return false; // Otherwise, we cannot eliminate the tail recursion!
}
+ }
// We can only transform call/return pairs that either ignore the return value
// of the call and return void, ignore the value of the call and return a
// constant, return the value returned by the tail call, or that are being
// accumulator recursion variable eliminated.
- if (Ret->getNumOperands() != 0 && Ret->getReturnValue() != CI &&
+ if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
+ !isa<UndefValue>(Ret->getReturnValue()) &&
AccumulatorRecursionEliminationInitVal == 0 &&
- !getCommonReturnValue(Ret, CI))
- return false;
+ !getCommonReturnValue(0, CI)) {
+ // One case remains that we are able to handle: the current return
+ // instruction returns a constant, and all other return instructions
+ // return a different constant.
+ if (!isDynamicConstant(Ret->getReturnValue(), CI, Ret))
+ return false; // Current return instruction does not return a constant.
+ // Check that all other return instructions return a common constant. If
+ // so, record it in AccumulatorRecursionEliminationInitVal.
+ AccumulatorRecursionEliminationInitVal = getCommonReturnValue(Ret, CI);
+ if (!AccumulatorRecursionEliminationInitVal)
+ return false;
+ }
+
+ BasicBlock *BB = Ret->getParent();
+ Function *F = BB->getParent();
// OK! We can transform this tail call. If this is the first one found,
// create the new entry block, allowing us to branch back to the old entry.
if (OldEntry == 0) {
OldEntry = &F->getEntryBlock();
- std::string OldName = OldEntry->getName(); OldEntry->setName("tailrecurse");
- BasicBlock *NewEntry = new BasicBlock(OldName, F, OldEntry);
- new BranchInst(OldEntry, NewEntry);
-
+ BasicBlock *NewEntry = BasicBlock::Create(F->getContext(), "", F, OldEntry);
+ NewEntry->takeName(OldEntry);
+ OldEntry->setName("tailrecurse");
+ BranchInst::Create(OldEntry, NewEntry);
+
+ // If this tail call is marked 'tail' and if there are any allocas in the
+ // entry block, move them up to the new entry block.
+ TailCallsAreMarkedTail = CI->isTailCall();
+ if (TailCallsAreMarkedTail)
+ // Move all fixed sized allocas from OldEntry to NewEntry.
+ for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(),
+ NEBI = NewEntry->begin(); OEBI != E; )
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++))
+ if (isa<ConstantInt>(AI->getArraySize()))
+ AI->moveBefore(NEBI);
+
// Now that we have created a new block, which jumps to the entry
// block, insert a PHI node for each argument of the function.
// For now, we initialize each PHI to only have the real arguments
// which are passed in.
Instruction *InsertPos = OldEntry->begin();
- for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I) {
- PHINode *PN = new PHINode(I->getType(), I->getName()+".tr", InsertPos);
+ for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
+ I != E; ++I) {
+ PHINode *PN = PHINode::Create(I->getType(), 2,
+ I->getName() + ".tr", InsertPos);
I->replaceAllUsesWith(PN); // Everyone use the PHI node now!
PN->addIncoming(I, NewEntry);
ArgumentPHIs.push_back(PN);
}
}
-
+
+ // If this function has self recursive calls in the tail position where some
+ // are marked tail and some are not, only transform one flavor or another. We
+ // have to choose whether we move allocas in the entry block to the new entry
+ // block or not, so we can't make a good choice for both. NOTE: We could do
+ // slightly better here in the case that the function has no entry block
+ // allocas.
+ if (TailCallsAreMarkedTail && !CI->isTailCall())
+ return false;
+
// Ok, now that we know we have a pseudo-entry block WITH all of the
// required PHI nodes, add entries into the PHI node for the actual
// parameters passed into the tail-recursive call.
- for (unsigned i = 0, e = CI->getNumOperands()-1; i != e; ++i)
- ArgumentPHIs[i]->addIncoming(CI->getOperand(i+1), BB);
-
+ for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i)
+ ArgumentPHIs[i]->addIncoming(CI->getArgOperand(i), BB);
+
// If we are introducing an accumulator variable to eliminate the recursion,
// do so now. Note that we _know_ that no subsequent tail recursion
// eliminations will happen on this function because of the way the
if (AccumulatorRecursionEliminationInitVal) {
Instruction *AccRecInstr = AccumulatorRecursionInstr;
// Start by inserting a new PHI node for the accumulator.
- PHINode *AccPN = new PHINode(AccRecInstr->getType(), "accumulator.tr",
- OldEntry->begin());
+ pred_iterator PB = pred_begin(OldEntry), PE = pred_end(OldEntry);
+ PHINode *AccPN =
+ PHINode::Create(AccumulatorRecursionEliminationInitVal->getType(),
+ std::distance(PB, PE) + 1,
+ "accumulator.tr", OldEntry->begin());
// Loop over all of the predecessors of the tail recursion block. For the
// real entry into the function we seed the PHI with the initial value,
// other tail recursions eliminated) the accumulator is not modified.
// Because we haven't added the branch in the current block to OldEntry yet,
// it will not show up as a predecessor.
- for (pred_iterator PI = pred_begin(OldEntry), PE = pred_end(OldEntry);
- PI != PE; ++PI) {
- if (*PI == &F->getEntryBlock())
- AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, *PI);
+ for (pred_iterator PI = PB; PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ if (P == &F->getEntryBlock())
+ AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, P);
else
- AccPN->addIncoming(AccPN, *PI);
+ AccPN->addIncoming(AccPN, P);
}
- // Add an incoming argument for the current block, which is computed by our
- // associative accumulator instruction.
- AccPN->addIncoming(AccRecInstr, BB);
-
- // Next, rewrite the accumulator recursion instruction so that it does not
- // use the result of the call anymore, instead, use the PHI node we just
- // inserted.
- AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
+ if (AccRecInstr) {
+ // Add an incoming argument for the current block, which is computed by
+ // our associative and commutative accumulator instruction.
+ AccPN->addIncoming(AccRecInstr, BB);
+
+ // Next, rewrite the accumulator recursion instruction so that it does not
+ // use the result of the call anymore, instead, use the PHI node we just
+ // inserted.
+ AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
+ } else {
+ // Add an incoming argument for the current block, which is just the
+ // constant returned by the current return instruction.
+ AccPN->addIncoming(Ret->getReturnValue(), BB);
+ }
// Finally, rewrite any return instructions in the program to return the PHI
// node instead of the "initval" that they do currently. This loop will
// Now that all of the PHI nodes are in place, remove the call and
// ret instructions, replacing them with an unconditional branch.
- new BranchInst(OldEntry, Ret);
+ BranchInst *NewBI = BranchInst::Create(OldEntry, Ret);
+ NewBI->setDebugLoc(CI->getDebugLoc());
+
BB->getInstList().erase(Ret); // Remove return.
BB->getInstList().erase(CI); // Remove call.
++NumEliminated;
return true;
}
+
+bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB,
+ ReturnInst *Ret, BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail) {
+ bool Change = false;
+
+ // If the return block contains nothing but the return and PHI's,
+ // there might be an opportunity to duplicate the return in its
+ // predecessors and perform TRC there. Look for predecessors that end
+ // in unconditional branch and recursive call(s).
+ SmallVector<BranchInst*, 8> UncondBranchPreds;
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *Pred = *PI;
+ TerminatorInst *PTI = Pred->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
+ if (BI->isUnconditional())
+ UncondBranchPreds.push_back(BI);
+ }
+
+ while (!UncondBranchPreds.empty()) {
+ BranchInst *BI = UncondBranchPreds.pop_back_val();
+ BasicBlock *Pred = BI->getParent();
+ if (CallInst *CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail)){
+ DEBUG(dbgs() << "FOLDING: " << *BB
+ << "INTO UNCOND BRANCH PRED: " << *Pred);
+ EliminateRecursiveTailCall(CI, FoldReturnIntoUncondBranch(Ret, BB, Pred),
+ OldEntry, TailCallsAreMarkedTail, ArgumentPHIs,
+ CannotTailCallElimCallsMarkedTail);
+ ++NumRetDuped;
+ Change = true;
+ }
+ }
+
+ return Change;
+}
+
+bool
+TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
+ bool &TailCallsAreMarkedTail,
+ SmallVectorImpl<PHINode *> &ArgumentPHIs,
+ bool CannotTailCallElimCallsMarkedTail) {
+ CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail);
+ if (!CI)
+ return false;
+
+ return EliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail,
+ ArgumentPHIs,
+ CannotTailCallElimCallsMarkedTail);
+}