diff options
| -rw-r--r-- | lib/Transforms/Scalar/IndVarSimplify.cpp | 1213 |
1 files changed, 624 insertions, 589 deletions
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 31dbd42f2c..677e7908f5 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -126,6 +126,11 @@ namespace { bool isValidRewrite(Value *FromVal, Value *ToVal); + void HandleFloatingPointIV(Loop *L, PHINode *PH); + void RewriteNonIntegerIVs(Loop *L); + + void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); + void SimplifyIVUsers(SCEVExpander &Rewriter); void SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter); @@ -134,22 +139,16 @@ namespace { void EliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand, bool IsSigned); - bool isSimpleIVUser(Instruction *I, const Loop *L); - void RewriteNonIntegerIVs(Loop *L); - - ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, - PHINode *IndVar, - SCEVExpander &Rewriter); - - void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); void SimplifyCongruentIVs(Loop *L); void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); - void SinkUnusedInvariants(Loop *L); + ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *IVLimit, + PHINode *IndVar, + SCEVExpander &Rewriter); - void HandleFloatingPointIV(Loop *L, PHINode *PH); + void SinkUnusedInvariants(Loop *L); }; } @@ -216,156 +215,262 @@ bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { return true; } -/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken -/// count expression can be safely and cheaply expanded into an instruction -/// sequence that can be used by LinearFunctionTestReplace. -static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) { - const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); - if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || - BackedgeTakenCount->isZero()) - return false; +//===----------------------------------------------------------------------===// +// RewriteNonIntegerIVs and helpers. Prefer integer IVs. +//===----------------------------------------------------------------------===// - if (!L->getExitingBlock()) +/// ConvertToSInt - Convert APF to an integer, if possible. +static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { + bool isExact = false; + if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) return false; - - // Can't rewrite non-branch yet. - BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); - if (!BI) + // See if we can convert this to an int64_t + uint64_t UIntVal; + if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, + &isExact) != APFloat::opOK || !isExact) return false; - - // Special case: If the backedge-taken count is a UDiv, it's very likely a - // UDiv that ScalarEvolution produced in order to compute a precise - // expression, rather than a UDiv from the user's code. If we can't find a - // UDiv in the code with some simple searching, assume the former and forego - // rewriting the loop. - if (isa<SCEVUDivExpr>(BackedgeTakenCount)) { - ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); - if (!OrigCond) return false; - const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); - R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); - if (R != BackedgeTakenCount) { - const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); - L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); - if (L != BackedgeTakenCount) - return false; - } - } + IntVal = UIntVal; return true; } -/// getBackedgeIVType - Get the widest type used by the loop test after peeking -/// through Truncs. +/// HandleFloatingPointIV - If the loop has floating induction variable +/// then insert corresponding integer induction variable if possible. +/// For example, +/// for(double i = 0; i < 10000; ++i) +/// bar(i) +/// is converted into +/// for(int i = 0; i < 10000; ++i) +/// bar((double)i); /// -/// TODO: Unnecessary once LinearFunctionTestReplace is removed. -static const Type *getBackedgeIVType(Loop *L) { - if (!L->getExitingBlock()) - return 0; +void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { + unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); + unsigned BackEdge = IncomingEdge^1; - // Can't rewrite non-branch yet. - BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); - if (!BI) - return 0; + // Check incoming value. + ConstantFP *InitValueVal = + dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); - ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); - if (!Cond) - return 0; + int64_t InitValue; + if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) + return; - const Type *Ty = 0; - for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end(); - OI != OE; ++OI) { - assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types"); - TruncInst *Trunc = dyn_cast<TruncInst>(*OI); - if (!Trunc) - continue; + // Check IV increment. Reject this PN if increment operation is not + // an add or increment value can not be represented by an integer. + BinaryOperator *Incr = + dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); + if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; - return Trunc->getSrcTy(); + // If this is not an add of the PHI with a constantfp, or if the constant fp + // is not an integer, bail out. + ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); + int64_t IncValue; + if (IncValueVal == 0 || Incr->getOperand(0) != PN || + !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) + return; + + // Check Incr uses. One user is PN and the other user is an exit condition + // used by the conditional terminator. + Value::use_iterator IncrUse = Incr->use_begin(); + Instruction *U1 = cast<Instruction>(*IncrUse++); + if (IncrUse == Incr->use_end()) return; + Instruction *U2 = cast<Instruction>(*IncrUse++); + if (IncrUse != Incr->use_end()) return; + + // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't + // only used by a branch, we can't transform it. + FCmpInst *Compare = dyn_cast<FCmpInst>(U1); + if (!Compare) + Compare = dyn_cast<FCmpInst>(U2); + if (Compare == 0 || !Compare->hasOneUse() || + !isa<BranchInst>(Compare->use_back())) + return; + + BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); + + // We need to verify that the branch actually controls the iteration count + // of the loop. If not, the new IV can overflow and no one will notice. + // The branch block must be in the loop and one of the successors must be out + // of the loop. + assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); + if (!L->contains(TheBr->getParent()) || + (L->contains(TheBr->getSuccessor(0)) && + L->contains(TheBr->getSuccessor(1)))) + return; + + + // If it isn't a comparison with an integer-as-fp (the exit value), we can't + // transform it. + ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); + int64_t ExitValue; + if (ExitValueVal == 0 || + !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) + return; + + // Find new predicate for integer comparison. + CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; + switch (Compare->getPredicate()) { + default: return; // Unknown comparison. + case CmpInst::FCMP_OEQ: + case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; + case CmpInst::FCMP_ONE: + case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; + case CmpInst::FCMP_OGT: + case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; + case CmpInst::FCMP_OGE: + case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; + case CmpInst::FCMP_OLT: + case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; + case CmpInst::FCMP_OLE: + case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; } - return Ty; -} -/// LinearFunctionTestReplace - This method rewrites the exit condition of the -/// loop to be a canonical != comparison against the incremented loop induction -/// variable. This pass is able to rewrite the exit tests of any loop where the -/// SCEV analysis can determine a loop-invariant trip count of the loop, which -/// is actually a much broader range than just linear tests. -ICmpInst *IndVarSimplify:: -LinearFunctionTestReplace(Loop *L, - const SCEV *BackedgeTakenCount, - PHINode *IndVar, - SCEVExpander &Rewriter) { - assert(canExpandBackedgeTakenCount(L, SE) && "precondition"); - BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); + // We convert the floating point induction variable to a signed i32 value if + // we can. This is only safe if the comparison will not overflow in a way + // that won't be trapped by the integer equivalent operations. Check for this + // now. + // TODO: We could use i64 if it is native and the range requires it. - // If the exiting block is not the same as the backedge block, we must compare - // against the preincremented value, otherwise we prefer to compare against - // the post-incremented value. - Value *CmpIndVar; - const SCEV *RHS = BackedgeTakenCount; - if (L->getExitingBlock() == L->getLoopLatch()) { - // Add one to the "backedge-taken" count to get the trip count. - // If this addition may overflow, we have to be more pessimistic and - // cast the induction variable before doing the add. - const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0); - const SCEV *N = - SE->getAddExpr(BackedgeTakenCount, - SE->getConstant(BackedgeTakenCount->getType(), 1)); - if ((isa<SCEVConstant>(N) && !N->isZero()) || - SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { - // No overflow. Cast the sum. - RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType()); - } else { - // Potential overflow. Cast before doing the add. - RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, - IndVar->getType()); - RHS = SE->getAddExpr(RHS, - SE->getConstant(IndVar->getType(), 1)); + // The start/stride/exit values must all fit in signed i32. + if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) + return; + + // If not actually striding (add x, 0.0), avoid touching the code. + if (IncValue == 0) + return; + + // Positive and negative strides have different safety conditions. + if (IncValue > 0) { + // If we have a positive stride, we require the init to be less than the + // exit value and an equality or less than comparison. + if (InitValue >= ExitValue || + NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE) + return; + + uint32_t Range = uint32_t(ExitValue-InitValue); + if (NewPred == CmpInst::ICMP_SLE) { + // Normalize SLE -> SLT, check for infinite loop. + if (++Range == 0) return; // Range overflows. } - // The BackedgeTaken expression contains the number of times that the - // backedge branches to the loop header. This is one less than the - // number of times the loop executes, so use the incremented indvar. - CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); + unsigned Leftover = Range % uint32_t(IncValue); + + // If this is an equality comparison, we require that the strided value + // exactly land on the exit value, otherwise the IV condition will wrap + // around and do things the fp IV wouldn't. + if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && + Leftover != 0) + return; + + // If the stride would wrap around the i32 before exiting, we can't + // transform the IV. + if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) + return; + } else { - // We have to use the preincremented value... - RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, - IndVar->getType()); - CmpIndVar = IndVar; + // If we have a negative stride, we require the init to be greater than the + // exit value and an equality or greater than comparison. + if (InitValue >= ExitValue || + NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE) + return; + + uint32_t Range = uint32_t(InitValue-ExitValue); + if (NewPred == CmpInst::ICMP_SGE) { + // Normalize SGE -> SGT, check for infinite loop. + if (++Range == 0) return; // Range overflows. + } + + unsigned Leftover = Range % uint32_t(-IncValue); + + // If this is an equality comparison, we require that the strided value + // exactly land on the exit value, otherwise the IV condition will wrap + // around and do things the fp IV wouldn't. + if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && + Leftover != 0) + return; + + // If the stride would wrap around the i32 before exiting, we can't + // transform the IV. + if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) + return; } - // Expand the code for the iteration count. - assert(SE->isLoopInvariant(RHS, L) && - "Computed iteration count is not loop invariant!"); - Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI); + const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); - // Insert a new icmp_ne or icmp_eq instruction before the branch. - ICmpInst::Predicate Opcode; - if (L->contains(BI->getSuccessor(0))) - Opcode = ICmpInst::ICMP_NE; - else - Opcode = ICmpInst::ICMP_EQ; + // Insert new integer induction variable. + PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN); + NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), + PN->getIncomingBlock(IncomingEdge)); - DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" - << " LHS:" << *CmpIndVar << '\n' - << " op:\t" - << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" - << " RHS:\t" << *RHS << "\n"); + Value *NewAdd = + BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), + Incr->getName()+".int", Incr); + NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); - ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond"); - Cond->setDebugLoc(BI->getDebugLoc()); - Value *OrigCond = BI->getCondition(); - // It's tempting to use replaceAllUsesWith here to fully replace the old - // comparison, but that's not immediately safe, since users of the old - // comparison may not be dominated by the new comparison. Instead, just - // update the branch to use the new comparison; in the common case this - // will make old comparison dead. - BI->setCondition(Cond); - DeadInsts.push_back(OrigCond); + ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, + ConstantInt::get(Int32Ty, ExitValue), + Compare->getName()); - ++NumLFTR; - Changed = true; - return Cond; + // In the following deletions, PN may become dead and may be deleted. + // Use a WeakVH to observe whether this happens. + WeakVH WeakPH = PN; + + // Delete the old floating point exit comparison. The branch starts using the + // new comparison. + NewCompare->takeName(Compare); + Compare->replaceAllUsesWith(NewCompare); + RecursivelyDeleteTriviallyDeadInstructions(Compare); + + // Delete the old floating point increment. + Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); + RecursivelyDeleteTriviallyDeadInstructions(Incr); + + // If the FP induction variable still has uses, this is because something else + // in the loop uses its value. In order to canonicalize the induction + // variable, we chose to eliminate the IV and rewrite it in terms of an + // int->fp cast. + // + // We give preference to sitofp over uitofp because it is faster on most + // platforms. + if (WeakPH) { + Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", + PN->getParent()->getFirstNonPHI()); + PN->replaceAllUsesWith(Conv); + RecursivelyDeleteTriviallyDeadInstructions(PN); + } + + // Add a new IVUsers entry for the newly-created integer PHI. + if (IU) + IU->AddUsersIfInteresting(NewPHI); } +void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { + // First step. Check to see if there are any floating-point recurrences. + // If there are, change them into integer recurrences, permitting analysis by + // the SCEV routines. + // + BasicBlock *Header = L->getHeader(); + + SmallVector<WeakVH, 8> PHIs; + for (BasicBlock::iterator I = Header->begin(); + PHINode *PN = dyn_cast<PHINode>(I); ++I) + PHIs.push_back(PN); + + for (unsigned i = 0, e = PHIs.size(); i != e; ++i) + if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) + HandleFloatingPointIV(L, PN); + + // If the loop previously had floating-point IV, ScalarEvolution + // may not have been able to compute a trip count. Now that we've done some + // re-writing, the trip count may be computable. + if (Changed) + SE->forgetLoop(L); +} + +//===----------------------------------------------------------------------===// +// RewriteLoopExitValues - Optimize IV users outside the loop. +// As a side effect, reduces the amount of IV processing within the loop. +//===----------------------------------------------------------------------===// + /// RewriteLoopExitValues - Check to see if this loop has a computable /// loop-invariant execution count. If so, this means that we can compute the /// final value of any expressions that are recurrent in the loop, and @@ -479,28 +584,10 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { Rewriter.clearInsertPoint(); } -void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { - // First step. Check to see if there are any floating-point recurrences. - // If there are, change them into integer recurrences, permitting analysis by - // the SCEV routines. - // - BasicBlock *Header = L->getHeader(); - - SmallVector<WeakVH, 8> PHIs; - for (BasicBlock::iterator I = Header->begin(); - PHINode *PN = dyn_cast<PHINode>(I); ++I) - PHIs.push_back(PN); - - for (unsigned i = 0, e = PHIs.size(); i != e; ++i) - if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) - HandleFloatingPointIV(L, PN); - - // If the loop previously had floating-point IV, ScalarEvolution - // may not have been able to compute a trip count. Now that we've done some - // re-writing, the trip count may be computable. - if (Changed) - SE->forgetLoop(L); -} +//===----------------------------------------------------------------------===// +// Rewrite IV users based on a canonical IV. +// To be replaced by -disable-iv-rewrite. +//===----------------------------------------------------------------------===// /// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this /// loop. IVUsers is treated as a worklist. Each successive simplification may @@ -532,6 +619,133 @@ void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) { } } +// FIXME: It is an extremely bad idea to indvar substitute anything more +// complex than affine induction variables. Doing so will put expensive +// polynomial evaluations inside of the loop, and the str reduction pass +// currently can only reduce affine polynomials. For now just disable +// indvar subst on anything more complex than an affine addrec, unless +// it can be expanded to a trivial value. +static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) { + // Loop-invariant values are safe. + if (SE->isLoopInvariant(S, L)) return true; + + // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how + // to transform them into efficient code. + if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) + return AR->isAffine(); + + // An add is safe it all its operands are safe. + if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) { + for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(), + E = Commutative->op_end(); I != E; ++I) + if (!isSafe(*I, L, SE)) return false; + return true; + } + + // A cast is safe if its operand is. + if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) + return isSafe(C->getOperand(), L, SE); + + // A udiv is safe if its operands are. + if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) + return isSafe(UD->getLHS(), L, SE) && + isSafe(UD->getRHS(), L, SE); + + // SCEVUnknown is always safe. + if (isa<SCEVUnknown>(S)) + return true; + + // Nothing else is safe. + return false; +} + +void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) { + // Rewrite all induction variable expressions in terms of the canonical + // induction variable. + // + // If there were induction variables of other sizes or offsets, manually + // add the offsets to the primary induction variable and cast, avoiding + // the need for the code evaluation methods to insert induction variables + // of different sizes. + for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) { + Value *Op = UI->getOperandValToReplace(); + const Type *UseTy = Op->getType(); + Instruction *User = UI->getUser(); + + // Compute the final addrec to expand into code. + const SCEV *AR = IU->getReplacementExpr(*UI); + + // Evaluate the expression out of the loop, if possible. + if (!L->contains(UI->getUser())) { + const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop()); + if (SE->isLoopInvariant(ExitVal, L)) + AR = ExitVal; + } + + // FIXME: It is an extremely bad idea to indvar substitute anything more + // complex than affine induction variables. Doing so will put expensive + // polynomial evaluations inside of the loop, and the str reduction pass + // currently can only reduce affine polynomials. For now just disable + // indvar subst on anything more complex than an affine addrec, unless + // it can be expanded to a trivial value. + if (!isSafe(AR, L, SE)) + continue; + + // Determine the insertion point for this user. By default, insert + // immediately before the user. The SCEVExpander class will automatically + // hoist loop invariants out of the loop. For PHI nodes, there may be + // multiple uses, so compute the nearest common dominator for the + // incoming blocks. + Instruction *InsertPt = User; + if (PHINode *PHI = dyn_cast<PHINode>(InsertPt)) + for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) + if (PHI->getIncomingValue(i) == Op) { + if (InsertPt == User) + InsertPt = PHI->getIncomingBlock(i)->getTerminator(); + else + InsertPt = + DT->findNearestCommonDominator(InsertPt->getParent(), + PHI->getIncomingBlock(i)) + ->getTerminator(); + } + + // Now expand it into actual Instructions and patch it into place. + Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt); + + DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' + << " into = " << *NewVal << "\n"); + + if (!isValidRewrite(Op, NewVal)) { + DeadInsts.push_back(NewVal); + continue; + } + // Inform ScalarEvolution that this value is changing. The change doesn't + // affect its value, but it does potentially affect which use lists the + // value will be on after the replacement, which affects ScalarEvolution's + // ability to walk use lists and drop dangling pointers when a value is + // deleted. + SE->forgetValue(User); + + // Patch the new value into place. + if (Op->hasName()) + NewVal->takeName(Op); + if (Instruction *NewValI = dyn_cast<Instruction>(NewVal)) + NewValI->setDebugLoc(User->getDebugLoc()); + User->replaceUsesOfWith(Op, NewVal); + UI->setOperandValToReplace(NewVal); + + ++NumRemoved; + Changed = true; + + // The old value may be dead now. + DeadInsts.push_back(Op); + } +} + +//===----------------------------------------------------------------------===// +// IV Widening - Extend the width of an IV to cover its widest uses. +//===----------------------------------------------------------------------===// + namespace { // Collect information about induction variables that are used by sign/zero // extend operations. This information is recorded by CollectExtend and @@ -935,6 +1149,10 @@ PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) { return WidePhi; } +//===----------------------------------------------------------------------===// +// Simplification of IV users based on SCEV evaluation. +//===----------------------------------------------------------------------===// + void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) { unsigned IVOperIdx = 0; ICmpInst::Predicate Pred = ICmp->getPredicate(); @@ -1081,7 +1299,7 @@ static void pushIVUsers( /// This is similar to IVUsers' isInsteresting() but processes each instruction /// non-recursively when the operand is already known to be a simpleIVUser. /// -bool IndVarSimplify::isSimpleIVUser(Instruction *I, const Loop *L) { +static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) { if (!SE->isSCEVable(I->getType())) return false; @@ -1166,7 +1384,7 @@ void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) { } continue; } - if (isSimpleIVUser(UseInst, L)) { + if (isSimpleIVUser(UseInst, L, SE)) { pushIVUsers(UseInst, Simplified, SimpleIVUsers); } } @@ -1193,6 +1411,9 @@ void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) { void IndVarSimplify::SimplifyCongruentIVs(Loop *L) { for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { PHINode *Phi = cast<PHINode>(I); + if (!SE->isSCEVable(Phi->getType())) + continue; + const SCEV *S = SE->getSCEV(Phi); ExprToIVMapTy::const_iterator Pos; bool Inserted; @@ -1226,6 +1447,249 @@ void IndVarSimplify::SimplifyCongruentIVs(Loop *L) { } } +//===----------------------------------------------------------------------===// +// LinearFunctionTestReplace and its kin. Rewrite the loop exit condition. +//===----------------------------------------------------------------------===// + +/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken +/// count expression can be safely and cheaply expanded into an instruction +/// sequence that can be used by LinearFunctionTestReplace. +static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) { + const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); + if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || + BackedgeTakenCount->isZero()) + return false; + + if (!L->getExitingBlock()) + return false; + + // Can't rewrite non-branch yet. + BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); + if (!BI) + return false; + + // Special case: If the backedge-taken count is a UDiv, it's very likely a + // UDiv that ScalarEvolution produced in order to compute a precise + // expression, rather than a UDiv from the user's code. If we can't find a + // UDiv in the code with some simple searching, assume the former and forego + // rewriting the loop. + if (isa<SCEVUDivExpr>(BackedgeTakenCount)) { + ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); + if (!OrigCond) return false; + const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); + R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); + if (R != BackedgeTakenCount) { + const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); + L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); + if (L != BackedgeTakenCount) + return false; + } + } + return true; +} + +/// getBackedgeIVType - Get the widest type used by the loop test after peeking +/// through Truncs. +/// +/// TODO: Unnecessary if LFTR does not force a canonical IV. +static const Type *getBackedgeIVType(Loop *L) { + if (!L->getExitingBlock()) + return 0; + + // Can't rewrite non-branch yet. + BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); + if (!BI) + return 0; + + ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); + if (!Cond) + return 0; + + const Type *Ty = 0; + for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end(); + OI != OE; ++OI) { + assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types"); + TruncInst *Trunc = dyn_cast<TruncInst>(*OI); + if (!Trunc) + continue; + + return Trunc->getSrcTy(); + } + return Ty; +} + +/// LinearFunctionTestReplace - This method rewrites the exit condition of the +/// loop to be a canonical != comparison against the incremented loop induction +/// variable. This pass is able to rewrite the exit tests of any loop where the +/// SCEV analysis can determine a loop-invariant trip count of the loop, which +/// is actually a much broader range than just linear tests. +ICmpInst *IndVarSimplify:: +LinearFunctionTestReplace(Loop *L, + const SCEV *BackedgeTakenCount, + PHINode *IndVar, + SCEVExpander &Rewriter) { + assert(canExpandBackedgeTakenCount(L, SE) && "precondition"); + BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); + + // If the exiting block is not the same as the backedge block, we must compare + // against the preincremented value, otherwise we prefer to compare against + // the post-incremented value. + Value *CmpIndVar; + const SCEV *RHS = BackedgeTakenCount; + if (L->getExitingBlock() == L->getLoopLatch()) { + // Add one to the "backedge-taken" count to get the trip count. + // If this addition may overflow, we have to be more pessimistic and + // cast the induction variable before doing the add. + const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0); + const SCEV *N = + SE->getAddExpr(BackedgeTakenCount, + SE->getConstant(BackedgeTakenCount->getType(), 1)); + if ((isa<SCEVConstant>(N) && !N->isZero()) || + SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { + // No overflow. Cast the sum. + RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType()); + } else { + // Potential overflow. Cast before doing the add. + RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, + IndVar->getType()); + RHS = SE->getAddExpr(RHS, + SE->getConstant(IndVar->getType(), 1)); + } + + // The BackedgeTaken expression contains the number of times that the + // backedge branches to the loop header. This is one less than the + // number of times the loop executes, so use the incremented indvar. + CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); + } else { + // We have to use the preincremented value... + RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, + IndVar->getType()); + CmpIndVar = IndVar; + } + + // Expand the code for the iteration count. + assert(SE->isLoopInvariant(RHS, L) && + "Computed iteration count is not loop invariant!"); + Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI); + + // Insert a new icmp_ne or icmp_eq instruction before the branch. + ICmpInst::Predicate Opcode; + if (L->contains(BI->getSuccessor(0))) + Opcode = ICmpInst::ICMP_NE; + else + Opcode = ICmpInst::ICMP_EQ; + + DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" + << " LHS:" << *CmpIndVar << '\n' + << " op:\t" + << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" + << " RHS:\t" << *RHS << "\n"); + + ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond"); + Cond->setDebugLoc(BI->getDebugLoc()); + Value *OrigCond = BI->getCondition(); + // It's tempting to use replaceAllUsesWith here to fully replace the old + // comparison, but that's not immediately safe, since users of the old + // comparison may not be dominated by the new comparison. Instead, just + // update the branch to use the new comparison; in the common case this + // will make old comparison dead. + BI->setCondition(Cond); + DeadInsts.push_back(OrigCond); + + ++NumLFTR; + Changed = true; + return Cond; +} + +//===----------------------------------------------------------------------===// +// SinkUnusedInvariants. A late subpass to cleanup loop preheaders. +//===----------------------------------------------------------------------===// + +/// If there's a single exit block, sink any loop-invariant values that +/// were defined in the preheader but not used inside the loop into the +/// exit block to reduce register pressure in the loop. +void IndVarSimplify::SinkUnusedInvariants(Loop *L) { + BasicBlock *ExitBlock = L->getExitBlock(); + if (!ExitBlock) return; + + BasicBlock *Preheader = L->getLoopPreheader(); + if (!Preheader) return; + + Instruction *InsertPt = ExitBlock->getFirstNonPHI(); + BasicBlock::iterator I = Preheader->getTerminator(); + while (I != Preheader->begin()) { + --I; + // New instructions were inserted at the end of the preheader. + if (isa<PHINode>(I)) + break; + + // Don't move instructions which might have side effects, since the side + // effects need to complete before instructions inside the loop. Also don't + // move instructions which might read memory, since the loop may modify + // memory. Note that it's okay if the instruction might have undefined + // behavior: LoopSimplify guarantees that the preheader dominates the exit + // block. + if (I->mayHaveSideEffects() || I->mayReadFromMemory()) + continue; + + // Skip debug info intrinsics. + if (isa<DbgInfoIntrinsic>(I)) + continue; + + // Don't sink static AllocaInsts out of the entry block, which would + // turn them into dynamic allocas! + if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) + if (AI->isStaticAlloca()) + continue; + + // Determine if there is a use in or before the loop (direct or + // otherwise). + bool UsedInLoop = false; + for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); + UI != UE; ++UI) { + User *U = *UI; + BasicBlock *UseBB = cast<Instruction>(U)->getParent(); + if (PHINode *P = dyn_cast<PHINode>(U)) { + unsigned i = + PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); + UseBB = P->getIncomingBlock(i); + } + if (UseBB == Preheader || L->contains(UseBB)) { + UsedInLoop = true; + break; + } + } + + // If there is, the def must remain in the preheader. + if (UsedInLoop) + continue; + + // Otherwise, sink it to the exit block. + Instruction *ToMove = I; + bool Done = false; + + if (I != Preheader->begin()) { + // Skip debug info intrinsics. + do { + --I; + } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); + + if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) + Done = true; + } else { + Done = true; + } + + ToMove->moveBefore(InsertPt); + if (Done) break; + InsertPt = ToMove; + } +} + +//===----------------------------------------------------------------------===// +// IndVarSimplify driver. Manage several subpasses of IV simplification. +//===----------------------------------------------------------------------===// + bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { // If LoopSimplify form is not available, stay out of trouble. Some notes: // - LSR currently only supports LoopSimplify-form loops. Indvars' @@ -1364,8 +1828,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { "canonical IV disrupted BackedgeTaken expansion"); assert(NeedCannIV && "LinearFunctionTestReplace requires a canonical induction variable"); - NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, - Rewriter); + NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter); } // Rewrite IV-derived expressions. if (!DisableIVRewrite) @@ -1401,431 +1864,3 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!"); return Changed; } - -// FIXME: It is an extremely bad idea to indvar substitute anything more -// complex than affine induction variables. Doing so will put expensive -// polynomial evaluations inside of the loop, and the str reduction pass |