// 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 theier caller stack frame,
+// 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).
//
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
+#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/InlineCost.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Support/CallSite.h"
#include "llvm/Support/CFG.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
private:
bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
- std::vector<PHINode*> &ArgumentPHIs,
+ SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail);
bool CanMoveAboveCall(Instruction *I, CallInst *CI);
Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI);
return new TailCallElim();
}
-
/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by
/// callees of this function. We only do very simple analysis right now, this
/// could be expanded in the future to use mod/ref information for particular
return true;
}
-/// FunctionContainsAllocas - Scan the specified basic block for alloca
+/// CheckForEscapingAllocas - Scan the specified basic block for alloca
/// instructions. If it contains any that might be accessed by calls, return
/// true.
static bool CheckForEscapingAllocas(BasicBlock *BB,
BasicBlock *OldEntry = 0;
bool TailCallsAreMarkedTail = false;
- std::vector<PHINode*> ArgumentPHIs;
+ SmallVector<PHINode*, 8> ArgumentPHIs;
bool MadeChange = false;
bool FunctionContainsEscapingAllocas = false;
/// happen. This bug is PR962.
if (FunctionContainsEscapingAllocas)
return false;
-
// Second pass, change any tail calls to loops.
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (I->mayHaveSideEffects()) // This also handles volatile loads.
return false;
- if (LoadInst* L = dyn_cast<LoadInst>(I)) {
+ 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
// FIXME: Writes to memory only matter if they may alias the pointer
// being loaded from.
if (CI->mayWriteToMemory() ||
- !isSafeToLoadUnconditionally(L->getPointerOperand(), L))
+ !isSafeToLoadUnconditionally(L->getPointerOperand(), L,
+ L->getAlignment()))
return false;
}
}
// 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
// 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;
- // TODO: Handle multiple value ret instructions;
- if (isa<StructType>(F->getReturnType()))
- return 0;
-
for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()))
- if (RI != TheRI) {
+ if (RI != IgnoreRI) {
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))
+ if (!isDynamicConstant(RetOp, CI, RI))
return 0;
if (ReturnedValue && RetOp != 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) ||
bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
bool &TailCallsAreMarkedTail,
- std::vector<PHINode*> &ArgumentPHIs,
+ SmallVector<PHINode*, 8> &ArgumentPHIs,
bool CannotTailCallElimCallsMarkedTail) {
BasicBlock *BB = Ret->getParent();
Function *F = BB->getParent();
if (&BB->front() == Ret) // Make sure there is something before the ret...
return false;
- // If the return is in the entry block, then making this transformation would
- // turn infinite recursion into an infinite loop. This transformation is ok
- // in theory, but breaks some code like:
- // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
- // disable this xform in this case, because the code generator will lower the
- // call to fabs into inline code.
- if (BB == &F->getEntryBlock())
- return false;
-
// 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;
if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail)
return false;
- // 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.
+ // 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() &&
+ &BB->front() == CI && &*++BB->begin() == Ret &&
+ callIsSmall(F)) {
+ // 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 false;
+ }
+
+ // 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.
Value *AccumulatorRecursionEliminationInitVal = 0;
Instruction *AccumulatorRecursionInstr = 0;
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.
+ // is an associative and commutative 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
if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
!isa<UndefValue>(Ret->getReturnValue()) &&
AccumulatorRecursionEliminationInitVal == 0 &&
- !getCommonReturnValue(Ret, CI))
+ !getCommonReturnValue(0, CI))
return false;
// OK! We can transform this tail call. If this is the first one found,
// 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
// 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);
+ 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.
+ // associative and commutative accumulator instruction.
AccPN->addIncoming(AccRecInstr, BB);
// Next, rewrite the accumulator recursion instruction so that it does not