| //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This transformation analyzes and transforms the induction variables (and |
| // computations derived from them) into simpler forms suitable for subsequent |
| // analysis and transformation. |
| // |
| // This transformation makes the following changes to each loop with an |
| // identifiable induction variable: |
| // 1. All loops are transformed to have a SINGLE canonical induction variable |
| // which starts at zero and steps by one. |
| // 2. The canonical induction variable is guaranteed to be the first PHI node |
| // in the loop header block. |
| // 3. The canonical induction variable is guaranteed to be in a wide enough |
| // type so that IV expressions need not be (directly) zero-extended or |
| // sign-extended. |
| // 4. Any pointer arithmetic recurrences are raised to use array subscripts. |
| // |
| // If the trip count of a loop is computable, this pass also makes the following |
| // changes: |
| // 1. The exit condition for the loop is canonicalized to compare the |
| // induction value against the exit value. This turns loops like: |
| // 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' |
| // 2. Any use outside of the loop of an expression derived from the indvar |
| // is changed to compute the derived value outside of the loop, eliminating |
| // the dependence on the exit value of the induction variable. If the only |
| // purpose of the loop is to compute the exit value of some derived |
| // expression, this transformation will make the loop dead. |
| // |
| // This transformation should be followed by strength reduction after all of the |
| // desired loop transformations have been performed. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "indvars" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/BasicBlock.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/LLVMContext.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/IVUsers.h" |
| #include "llvm/Analysis/ScalarEvolutionExpander.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| using namespace llvm; |
| |
| STATISTIC(NumRemoved , "Number of aux indvars removed"); |
| STATISTIC(NumInserted, "Number of canonical indvars added"); |
| STATISTIC(NumReplaced, "Number of exit values replaced"); |
| STATISTIC(NumLFTR , "Number of loop exit tests replaced"); |
| |
| namespace { |
| class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass { |
| IVUsers *IU; |
| LoopInfo *LI; |
| ScalarEvolution *SE; |
| DominatorTree *DT; |
| bool Changed; |
| public: |
| |
| static char ID; // Pass identification, replacement for typeid |
| IndVarSimplify() : LoopPass(&ID) {} |
| |
| virtual bool runOnLoop(Loop *L, LPPassManager &LPM); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<LoopInfo>(); |
| AU.addRequired<ScalarEvolution>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addRequiredID(LCSSAID); |
| AU.addRequired<IVUsers>(); |
| AU.addPreserved<ScalarEvolution>(); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addPreservedID(LCSSAID); |
| AU.addPreserved<IVUsers>(); |
| AU.setPreservesCFG(); |
| } |
| |
| private: |
| |
| void RewriteNonIntegerIVs(Loop *L); |
| |
| ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, |
| Value *IndVar, |
| BasicBlock *ExitingBlock, |
| BranchInst *BI, |
| SCEVExpander &Rewriter); |
| void RewriteLoopExitValues(Loop *L, const SCEV *BackedgeTakenCount, |
| SCEVExpander &Rewriter); |
| |
| void RewriteIVExpressions(Loop *L, const Type *LargestType, |
| SCEVExpander &Rewriter); |
| |
| void SinkUnusedInvariants(Loop *L); |
| |
| void HandleFloatingPointIV(Loop *L, PHINode *PH); |
| }; |
| } |
| |
| char IndVarSimplify::ID = 0; |
| static RegisterPass<IndVarSimplify> |
| X("indvars", "Canonicalize Induction Variables"); |
| |
| Pass *llvm::createIndVarSimplifyPass() { |
| return new IndVarSimplify(); |
| } |
| |
| /// 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, |
| Value *IndVar, |
| BasicBlock *ExitingBlock, |
| BranchInst *BI, |
| SCEVExpander &Rewriter) { |
| // 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 (ExitingBlock == 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->getIntegerSCEV(0, BackedgeTakenCount->getType()); |
| const SCEV *N = |
| SE->getAddExpr(BackedgeTakenCount, |
| SE->getIntegerSCEV(1, BackedgeTakenCount->getType())); |
| if ((isa<SCEVConstant>(N) && !N->isZero()) || |
| SE->isLoopGuardedByCond(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->getIntegerSCEV(1, IndVar->getType())); |
| } |
| |
| // 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 = L->getCanonicalInductionVariableIncrement(); |
| } else { |
| // We have to use the preincremented value... |
| RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, |
| IndVar->getType()); |
| CmpIndVar = IndVar; |
| } |
| |
| // Expand the code for the iteration count. |
| assert(RHS->isLoopInvariant(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; |
| |
| DOUT << "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"); |
| |
| Instruction *OrigCond = cast<Instruction>(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); |
| RecursivelyDeleteTriviallyDeadInstructions(OrigCond); |
| |
| ++NumLFTR; |
| Changed = true; |
| return Cond; |
| } |
| |
| /// 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 |
| /// substitute the exit values from the loop into any instructions outside of |
| /// the loop that use the final values of the current expressions. |
| /// |
| /// This is mostly redundant with the regular IndVarSimplify activities that |
| /// happen later, except that it's more powerful in some cases, because it's |
| /// able to brute-force evaluate arbitrary instructions as long as they have |
| /// constant operands at the beginning of the loop. |
| void IndVarSimplify::RewriteLoopExitValues(Loop *L, |
| const SCEV *BackedgeTakenCount, |
| SCEVExpander &Rewriter) { |
| // Verify the input to the pass in already in LCSSA form. |
| assert(L->isLCSSAForm()); |
| |
| SmallVector<BasicBlock*, 8> ExitBlocks; |
| L->getUniqueExitBlocks(ExitBlocks); |
| |
| // Find all values that are computed inside the loop, but used outside of it. |
| // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan |
| // the exit blocks of the loop to find them. |
| for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { |
| BasicBlock *ExitBB = ExitBlocks[i]; |
| |
| // If there are no PHI nodes in this exit block, then no values defined |
| // inside the loop are used on this path, skip it. |
| PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); |
| if (!PN) continue; |
| |
| unsigned NumPreds = PN->getNumIncomingValues(); |
| |
| // Iterate over all of the PHI nodes. |
| BasicBlock::iterator BBI = ExitBB->begin(); |
| while ((PN = dyn_cast<PHINode>(BBI++))) { |
| if (PN->use_empty()) |
| continue; // dead use, don't replace it |
| // Iterate over all of the values in all the PHI nodes. |
| for (unsigned i = 0; i != NumPreds; ++i) { |
| // If the value being merged in is not integer or is not defined |
| // in the loop, skip it. |
| Value *InVal = PN->getIncomingValue(i); |
| if (!isa<Instruction>(InVal) || |
| // SCEV only supports integer expressions for now. |
| (!isa<IntegerType>(InVal->getType()) && |
| !isa<PointerType>(InVal->getType()))) |
| continue; |
| |
| // If this pred is for a subloop, not L itself, skip it. |
| if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) |
| continue; // The Block is in a subloop, skip it. |
| |
| // Check that InVal is defined in the loop. |
| Instruction *Inst = cast<Instruction>(InVal); |
| if (!L->contains(Inst->getParent())) |
| continue; |
| |
| // Okay, this instruction has a user outside of the current loop |
| // and varies predictably *inside* the loop. Evaluate the value it |
| // contains when the loop exits, if possible. |
| const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); |
| if (!ExitValue->isLoopInvariant(L)) |
| continue; |
| |
| Changed = true; |
| ++NumReplaced; |
| |
| Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); |
| |
| DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' |
| << " LoopVal = " << *Inst << "\n"; |
| |
| PN->setIncomingValue(i, ExitVal); |
| |
| // If this instruction is dead now, delete it. |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| |
| if (NumPreds == 1) { |
| // Completely replace a single-pred PHI. This is safe, because the |
| // NewVal won't be variant in the loop, so we don't need an LCSSA phi |
| // node anymore. |
| PN->replaceAllUsesWith(ExitVal); |
| RecursivelyDeleteTriviallyDeadInstructions(PN); |
| } |
| } |
| if (NumPreds != 1) { |
| // Clone the PHI and delete the original one. This lets IVUsers and |
| // any other maps purge the original user from their records. |
| PHINode *NewPN = PN->clone(PN->getContext()); |
| NewPN->takeName(PN); |
| NewPN->insertBefore(PN); |
| PN->replaceAllUsesWith(NewPN); |
| PN->eraseFromParent(); |
| } |
| } |
| } |
| } |
| |
| 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->forgetLoopBackedgeTakenCount(L); |
| } |
| |
| bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { |
| IU = &getAnalysis<IVUsers>(); |
| LI = &getAnalysis<LoopInfo>(); |
| SE = &getAnalysis<ScalarEvolution>(); |
| DT = &getAnalysis<DominatorTree>(); |
| Changed = false; |
| |
| // If there are any floating-point recurrences, attempt to |
| // transform them to use integer recurrences. |
| RewriteNonIntegerIVs(L); |
| |
| BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null |
| const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); |
| |
| // Create a rewriter object which we'll use to transform the code with. |
| SCEVExpander Rewriter(*SE); |
| |
| // 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 substitute the exit values from the |
| // loop into any instructions outside of the loop that use the final values of |
| // the current expressions. |
| // |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) |
| RewriteLoopExitValues(L, BackedgeTakenCount, Rewriter); |
| |
| // Compute the type of the largest recurrence expression, and decide whether |
| // a canonical induction variable should be inserted. |
| const Type *LargestType = 0; |
| bool NeedCannIV = false; |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) { |
| LargestType = BackedgeTakenCount->getType(); |
| LargestType = SE->getEffectiveSCEVType(LargestType); |
| // If we have a known trip count and a single exit block, we'll be |
| // rewriting the loop exit test condition below, which requires a |
| // canonical induction variable. |
| if (ExitingBlock) |
| NeedCannIV = true; |
| } |
| for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { |
| const SCEV *Stride = IU->StrideOrder[i]; |
| const Type *Ty = SE->getEffectiveSCEVType(Stride->getType()); |
| if (!LargestType || |
| SE->getTypeSizeInBits(Ty) > |
| SE->getTypeSizeInBits(LargestType)) |
| LargestType = Ty; |
| |
| std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = |
| IU->IVUsesByStride.find(IU->StrideOrder[i]); |
| assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); |
| |
| if (!SI->second->Users.empty()) |
| NeedCannIV = true; |
| } |
| |
| // Now that we know the largest of of the induction variable expressions |
| // in this loop, insert a canonical induction variable of the largest size. |
| Value *IndVar = 0; |
| if (NeedCannIV) { |
| // Check to see if the loop already has a canonical-looking induction |
| // variable. If one is present and it's wider than the planned canonical |
| // induction variable, temporarily remove it, so that the Rewriter |
| // doesn't attempt to reuse it. |
| PHINode *OldCannIV = L->getCanonicalInductionVariable(); |
| if (OldCannIV) { |
| if (SE->getTypeSizeInBits(OldCannIV->getType()) > |
| SE->getTypeSizeInBits(LargestType)) |
| OldCannIV->removeFromParent(); |
| else |
| OldCannIV = 0; |
| } |
| |
| IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType); |
| |
| ++NumInserted; |
| Changed = true; |
| DOUT << "INDVARS: New CanIV: " << *IndVar << '\n'; |
| |
| // Now that the official induction variable is established, reinsert |
| // the old canonical-looking variable after it so that the IR remains |
| // consistent. It will be deleted as part of the dead-PHI deletion at |
| // the end of the pass. |
| if (OldCannIV) |
| OldCannIV->insertAfter(cast<Instruction>(IndVar)); |
| } |
| |
| // If we have a trip count expression, rewrite the loop's exit condition |
| // using it. We can currently only handle loops with a single exit. |
| ICmpInst *NewICmp = 0; |
| if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock) { |
| assert(NeedCannIV && |
| "LinearFunctionTestReplace requires a canonical induction variable"); |
| // Can't rewrite non-branch yet. |
| if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) |
| NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, |
| ExitingBlock, BI, Rewriter); |
| } |
| |
| // Rewrite IV-derived expressions. Clears the rewriter cache. |
| RewriteIVExpressions(L, LargestType, Rewriter); |
| |
| // The Rewriter may not be used from this point on. |
| |
| // Loop-invariant instructions in the preheader that aren't used in the |
| // loop may be sunk below the loop to reduce register pressure. |
| SinkUnusedInvariants(L); |
| |
| // For completeness, inform IVUsers of the IV use in the newly-created |
| // loop exit test instruction. |
| if (NewICmp) |
| IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0))); |
| |
| // Clean up dead instructions. |
| DeleteDeadPHIs(L->getHeader()); |
| // Check a post-condition. |
| assert(L->isLCSSAForm() && "Indvars did not leave the loop in lcssa form!"); |
| return Changed; |
| } |
| |
| void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType, |
| SCEVExpander &Rewriter) { |
| SmallVector<WeakVH, 16> DeadInsts; |
| |
| // 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 (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { |
| const SCEV *Stride = IU->StrideOrder[i]; |
| |
| std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = |
| IU->IVUsesByStride.find(IU->StrideOrder[i]); |
| assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); |
| ilist<IVStrideUse> &List = SI->second->Users; |
| for (ilist<IVStrideUse>::iterator UI = List.begin(), |
| E = List.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); |
| |
| // 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 (!AR->isLoopInvariant(L) && !Stride->isLoopInvariant(L)) |
| 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); |
| |
| // Patch the new value into place. |
| if (Op->hasName()) |
| NewVal->takeName(Op); |
| User->replaceUsesOfWith(Op, NewVal); |
| UI->setOperandValToReplace(NewVal); |
| DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' |
| << " into = " << *NewVal << "\n"; |
| ++NumRemoved; |
| Changed = true; |
| |
| // The old value may be dead now. |
| DeadInsts.push_back(Op); |
| } |
| } |
| |
| // Clear the rewriter cache, because values that are in the rewriter's cache |
| // can be deleted in the loop below, causing the AssertingVH in the cache to |
| // trigger. |
| Rewriter.clear(); |
| // Now that we're done iterating through lists, clean up any instructions |
| // which are now dead. |
| while (!DeadInsts.empty()) { |
| Instruction *Inst = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()); |
| if (Inst) |
| RecursivelyDeleteTriviallyDeadInstructions(Inst); |
| } |
| } |
| |
| /// 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; |
| |
| Instruction *InsertPt = ExitBlock->getFirstNonPHI(); |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| 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; |
| // 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) { |
| BasicBlock *UseBB = cast<Instruction>(UI)->getParent(); |
| if (PHINode *P = dyn_cast<PHINode>(UI)) { |
| 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()) |
| --I; |
| else |
| Done = true; |
| ToMove->moveBefore(InsertPt); |
| if (Done) |
| break; |
| InsertPt = ToMove; |
| } |
| } |
| |
| /// Return true if it is OK to use SIToFPInst for an inducation variable |
| /// with given inital and exit values. |
| static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV, |
| uint64_t intIV, uint64_t intEV) { |
| |
| if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative()) |
| return true; |
| |
| // If the iteration range can be handled by SIToFPInst then use it. |
| APInt Max = APInt::getSignedMaxValue(32); |
| if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV))) |
| return true; |
| |
| return false; |
| } |
| |
| /// convertToInt - Convert APF to an integer, if possible. |
| static bool convertToInt(const APFloat &APF, uint64_t *intVal) { |
| |
| bool isExact = false; |
| if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) |
| return false; |
| if (APF.convertToInteger(intVal, 32, APF.isNegative(), |
| APFloat::rmTowardZero, &isExact) |
| != APFloat::opOK) |
| return false; |
| if (!isExact) |
| return false; |
| return true; |
| |
| } |
| |
| /// 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); |
| /// |
| void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) { |
| |
| unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0)); |
| unsigned BackEdge = IncomingEdge^1; |
| |
| // Check incoming value. |
| ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge)); |
| if (!InitValue) return; |
| uint64_t newInitValue = |
| Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits(); |
| if (!convertToInt(InitValue->getValueAPF(), &newInitValue)) |
| return; |
| |
| // Check IV increment. Reject this PH if increement operation is not |
| // an add or increment value can not be represented by an integer. |
| BinaryOperator *Incr = |
| dyn_cast<BinaryOperator>(PH->getIncomingValue(BackEdge)); |
| if (!Incr) return; |
| if (Incr->getOpcode() != Instruction::FAdd) return; |
| ConstantFP *IncrValue = NULL; |
| unsigned IncrVIndex = 1; |
| if (Incr->getOperand(1) == PH) |
| IncrVIndex = 0; |
| IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex)); |
| if (!IncrValue) return; |
| uint64_t newIncrValue = |
| Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits(); |
| if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue)) |
| return; |
| |
| // Check Incr uses. One user is PH and the other users is 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. |
| FCmpInst *EC = dyn_cast<FCmpInst>(U1); |
| if (!EC) |
| EC = dyn_cast<FCmpInst>(U2); |
| if (!EC) return; |
| |
| if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) { |
| if (!BI->isConditional()) return; |
| if (BI->getCondition() != EC) return; |
| } |
| |
| // Find exit value. If exit value can not be represented as an interger then |
| // do not handle this floating point PH. |
| ConstantFP *EV = NULL; |
| unsigned EVIndex = 1; |
| if (EC->getOperand(1) == Incr) |
| EVIndex = 0; |
| EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex)); |
| if (!EV) return; |
| uint64_t intEV = Type::getInt32Ty(PH->getContext())->getPrimitiveSizeInBits(); |
| if (!convertToInt(EV->getValueAPF(), &intEV)) |
| return; |
| |
| // Find new predicate for integer comparison. |
| CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; |
| switch (EC->getPredicate()) { |
| case CmpInst::FCMP_OEQ: |
| case CmpInst::FCMP_UEQ: |
| NewPred = CmpInst::ICMP_EQ; |
| break; |
| case CmpInst::FCMP_OGT: |
| case CmpInst::FCMP_UGT: |
| NewPred = CmpInst::ICMP_UGT; |
| break; |
| case CmpInst::FCMP_OGE: |
| case CmpInst::FCMP_UGE: |
| NewPred = CmpInst::ICMP_UGE; |
| break; |
| case CmpInst::FCMP_OLT: |
| case CmpInst::FCMP_ULT: |
| NewPred = CmpInst::ICMP_ULT; |
| break; |
| case CmpInst::FCMP_OLE: |
| case CmpInst::FCMP_ULE: |
| NewPred = CmpInst::ICMP_ULE; |
| break; |
| default: |
| break; |
| } |
| if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return; |
| |
| // Insert new integer induction variable. |
| PHINode *NewPHI = PHINode::Create(Type::getInt32Ty(PH->getContext()), |
| PH->getName()+".int", PH); |
| NewPHI->addIncoming(ConstantInt::get(Type::getInt32Ty(PH->getContext()), |
| newInitValue), |
| PH->getIncomingBlock(IncomingEdge)); |
| |
| Value *NewAdd = BinaryOperator::CreateAdd(NewPHI, |
| ConstantInt::get(Type::getInt32Ty(PH->getContext()), |
| newIncrValue), |
| Incr->getName()+".int", Incr); |
| NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge)); |
| |
| // The back edge is edge 1 of newPHI, whatever it may have been in the |
| // original PHI. |
| ConstantInt *NewEV = ConstantInt::get(Type::getInt32Ty(PH->getContext()), |
| intEV); |
| Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV); |
| Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1)); |
| ICmpInst *NewEC = new ICmpInst(EC->getParent()->getTerminator(), |
| NewPred, LHS, RHS, EC->getName()); |
| |
| // In the following deltions, PH may become dead and may be deleted. |
| // Use a WeakVH to observe whether this happens. |
| WeakVH WeakPH = PH; |
| |
| // Delete old, floating point, exit comparision instruction. |
| NewEC->takeName(EC); |
| EC->replaceAllUsesWith(NewEC); |
| RecursivelyDeleteTriviallyDeadInstructions(EC); |
| |
| // Delete old, floating point, increment instruction. |
| Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); |
| RecursivelyDeleteTriviallyDeadInstructions(Incr); |
| |
| // Replace floating induction variable, if it isn't already deleted. |
| // Give SIToFPInst preference over UIToFPInst because it is faster on |
| // platforms that are widely used. |
| if (WeakPH && !PH->use_empty()) { |
| if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) { |
| SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv", |
| PH->getParent()->getFirstNonPHI()); |
| PH->replaceAllUsesWith(Conv); |
| } else { |
| UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv", |
| PH->getParent()->getFirstNonPHI()); |
| PH->replaceAllUsesWith(Conv); |
| } |
| RecursivelyDeleteTriviallyDeadInstructions(PH); |
| } |
| |
| // Add a new IVUsers entry for the newly-created integer PHI. |
| IU->AddUsersIfInteresting(NewPHI); |
| } |