//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===// // // The LLVM Compiler Infrastructure // // This file was developed by Chris Lattner and is distributed under // the University of Illinois Open Source License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass munges the code in the input function to better prepare it for // SelectionDAG-based code generation. This works around limitations in it's // basic-block-at-a-time approach. It should eventually be removed. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "codegenprepare" #include "llvm/Transforms/Scalar.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/Instructions.h" #include "llvm/Pass.h" #include "llvm/Target/TargetAsmInfo.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/ADT/SmallSet.h" #include "llvm/Support/Debug.h" #include "llvm/Support/Compiler.h" using namespace llvm; namespace { class VISIBILITY_HIDDEN CodeGenPrepare : public FunctionPass { /// TLI - Keep a pointer of a TargetLowering to consult for determining /// transformation profitability. const TargetLowering *TLI; public: CodeGenPrepare(const TargetLowering *tli = 0) : TLI(tli) {} bool runOnFunction(Function &F); private: bool EliminateMostlyEmptyBlocks(Function &F); bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const; void EliminateMostlyEmptyBlock(BasicBlock *BB); bool OptimizeBlock(BasicBlock &BB); bool OptimizeGEPExpression(GetElementPtrInst *GEPI); }; } static RegisterPass X("codegenprepare", "Optimize for code generation"); FunctionPass *llvm::createCodeGenPreparePass(const TargetLowering *TLI) { return new CodeGenPrepare(TLI); } bool CodeGenPrepare::runOnFunction(Function &F) { bool EverMadeChange = false; // First pass, eliminate blocks that contain only PHI nodes and an // unconditional branch. EverMadeChange |= EliminateMostlyEmptyBlocks(F); bool MadeChange = true; while (MadeChange) { MadeChange = false; for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) MadeChange |= OptimizeBlock(*BB); EverMadeChange |= MadeChange; } return EverMadeChange; } /// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes /// and an unconditional branch. Passes before isel (e.g. LSR/loopsimplify) /// often split edges in ways that are non-optimal for isel. Start by /// eliminating these blocks so we can split them the way we want them. bool CodeGenPrepare::EliminateMostlyEmptyBlocks(Function &F) { bool MadeChange = false; // Note that this intentionally skips the entry block. for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ) { BasicBlock *BB = I++; // If this block doesn't end with an uncond branch, ignore it. BranchInst *BI = dyn_cast(BB->getTerminator()); if (!BI || !BI->isUnconditional()) continue; // If the instruction before the branch isn't a phi node, then other stuff // is happening here. BasicBlock::iterator BBI = BI; if (BBI != BB->begin()) { --BBI; if (!isa(BBI)) continue; } // Do not break infinite loops. BasicBlock *DestBB = BI->getSuccessor(0); if (DestBB == BB) continue; if (!CanMergeBlocks(BB, DestBB)) continue; EliminateMostlyEmptyBlock(BB); MadeChange = true; } return MadeChange; } /// CanMergeBlocks - Return true if we can merge BB into DestBB if there is a /// single uncond branch between them, and BB contains no other non-phi /// instructions. bool CodeGenPrepare::CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const { // We only want to eliminate blocks whose phi nodes are used by phi nodes in // the successor. If there are more complex condition (e.g. preheaders), // don't mess around with them. BasicBlock::const_iterator BBI = BB->begin(); while (const PHINode *PN = dyn_cast(BBI++)) { for (Value::use_const_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ++UI) { const Instruction *User = cast(*UI); if (User->getParent() != DestBB || !isa(User)) return false; } } // If BB and DestBB contain any common predecessors, then the phi nodes in BB // and DestBB may have conflicting incoming values for the block. If so, we // can't merge the block. const PHINode *DestBBPN = dyn_cast(DestBB->begin()); if (!DestBBPN) return true; // no conflict. // Collect the preds of BB. SmallPtrSet BBPreds; if (const PHINode *BBPN = dyn_cast(BB->begin())) { // It is faster to get preds from a PHI than with pred_iterator. for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) BBPreds.insert(BBPN->getIncomingBlock(i)); } else { BBPreds.insert(pred_begin(BB), pred_end(BB)); } // Walk the preds of DestBB. for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) { BasicBlock *Pred = DestBBPN->getIncomingBlock(i); if (BBPreds.count(Pred)) { // Common predecessor? BBI = DestBB->begin(); while (const PHINode *PN = dyn_cast(BBI++)) { const Value *V1 = PN->getIncomingValueForBlock(Pred); const Value *V2 = PN->getIncomingValueForBlock(BB); // If V2 is a phi node in BB, look up what the mapped value will be. if (const PHINode *V2PN = dyn_cast(V2)) if (V2PN->getParent() == BB) V2 = V2PN->getIncomingValueForBlock(Pred); // If there is a conflict, bail out. if (V1 != V2) return false; } } } return true; } /// EliminateMostlyEmptyBlock - Eliminate a basic block that have only phi's and /// an unconditional branch in it. void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) { BranchInst *BI = cast(BB->getTerminator()); BasicBlock *DestBB = BI->getSuccessor(0); DOUT << "MERGING MOSTLY EMPTY BLOCKS - BEFORE:\n" << *BB << *DestBB; // If the destination block has a single pred, then this is a trivial edge, // just collapse it. if (DestBB->getSinglePredecessor()) { // If DestBB has single-entry PHI nodes, fold them. while (PHINode *PN = dyn_cast(DestBB->begin())) { PN->replaceAllUsesWith(PN->getIncomingValue(0)); PN->eraseFromParent(); } // Splice all the PHI nodes from BB over to DestBB. DestBB->getInstList().splice(DestBB->begin(), BB->getInstList(), BB->begin(), BI); // Anything that branched to BB now branches to DestBB. BB->replaceAllUsesWith(DestBB); // Nuke BB. BB->eraseFromParent(); DOUT << "AFTER:\n" << *DestBB << "\n\n\n"; return; } // Otherwise, we have multiple predecessors of BB. Update the PHIs in DestBB // to handle the new incoming edges it is about to have. PHINode *PN; for (BasicBlock::iterator BBI = DestBB->begin(); (PN = dyn_cast(BBI)); ++BBI) { // Remove the incoming value for BB, and remember it. Value *InVal = PN->removeIncomingValue(BB, false); // Two options: either the InVal is a phi node defined in BB or it is some // value that dominates BB. PHINode *InValPhi = dyn_cast(InVal); if (InValPhi && InValPhi->getParent() == BB) { // Add all of the input values of the input PHI as inputs of this phi. for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i) PN->addIncoming(InValPhi->getIncomingValue(i), InValPhi->getIncomingBlock(i)); } else { // Otherwise, add one instance of the dominating value for each edge that // we will be adding. if (PHINode *BBPN = dyn_cast(BB->begin())) { for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) PN->addIncoming(InVal, BBPN->getIncomingBlock(i)); } else { for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) PN->addIncoming(InVal, *PI); } } } // The PHIs are now updated, change everything that refers to BB to use // DestBB and remove BB. BB->replaceAllUsesWith(DestBB); BB->eraseFromParent(); DOUT << "AFTER:\n" << *DestBB << "\n\n\n"; } /// SplitEdgeNicely - Split the critical edge from TI to it's specified /// successor if it will improve codegen. We only do this if the successor has /// phi nodes (otherwise critical edges are ok). If there is already another /// predecessor of the succ that is empty (and thus has no phi nodes), use it /// instead of introducing a new block. static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum, Pass *P) { BasicBlock *TIBB = TI->getParent(); BasicBlock *Dest = TI->getSuccessor(SuccNum); assert(isa(Dest->begin()) && "This should only be called if Dest has a PHI!"); /// TIPHIValues - This array is lazily computed to determine the values of /// PHIs in Dest that TI would provide. std::vector TIPHIValues; // Check to see if Dest has any blocks that can be used as a split edge for // this terminator. for (pred_iterator PI = pred_begin(Dest), E = pred_end(Dest); PI != E; ++PI) { BasicBlock *Pred = *PI; // To be usable, the pred has to end with an uncond branch to the dest. BranchInst *PredBr = dyn_cast(Pred->getTerminator()); if (!PredBr || !PredBr->isUnconditional() || // Must be empty other than the branch. &Pred->front() != PredBr) continue; // Finally, since we know that Dest has phi nodes in it, we have to make // sure that jumping to Pred will have the same affect as going to Dest in // terms of PHI values. PHINode *PN; unsigned PHINo = 0; bool FoundMatch = true; for (BasicBlock::iterator I = Dest->begin(); (PN = dyn_cast(I)); ++I, ++PHINo) { if (PHINo == TIPHIValues.size()) TIPHIValues.push_back(PN->getIncomingValueForBlock(TIBB)); // If the PHI entry doesn't work, we can't use this pred. if (TIPHIValues[PHINo] != PN->getIncomingValueForBlock(Pred)) { FoundMatch = false; break; } } // If we found a workable predecessor, change TI to branch to Succ. if (FoundMatch) { Dest->removePredecessor(TIBB); TI->setSuccessor(SuccNum, Pred); return; } } SplitCriticalEdge(TI, SuccNum, P, true); } /// InsertGEPComputeCode - Insert code into BB to compute Ptr+PtrOffset, /// casting to the type of GEPI. static Instruction *InsertGEPComputeCode(Instruction *&V, BasicBlock *BB, Instruction *GEPI, Value *Ptr, Value *PtrOffset) { if (V) return V; // Already computed. // Figure out the insertion point BasicBlock::iterator InsertPt; if (BB == GEPI->getParent()) { // If GEP is already inserted into BB, insert right after the GEP. InsertPt = GEPI; ++InsertPt; } else { // Otherwise, insert at the top of BB, after any PHI nodes InsertPt = BB->begin(); while (isa(InsertPt)) ++InsertPt; } // If Ptr is itself a cast, but in some other BB, emit a copy of the cast into // BB so that there is only one value live across basic blocks (the cast // operand). if (CastInst *CI = dyn_cast(Ptr)) if (CI->getParent() != BB && isa(CI->getOperand(0)->getType())) Ptr = CastInst::create(CI->getOpcode(), CI->getOperand(0), CI->getType(), "", InsertPt); // Add the offset, cast it to the right type. Ptr = BinaryOperator::createAdd(Ptr, PtrOffset, "", InsertPt); // Ptr is an integer type, GEPI is pointer type ==> IntToPtr return V = CastInst::create(Instruction::IntToPtr, Ptr, GEPI->getType(), "", InsertPt); } /// ReplaceUsesOfGEPInst - Replace all uses of RepPtr with inserted code to /// compute its value. The RepPtr value can be computed with Ptr+PtrOffset. One /// trivial way of doing this would be to evaluate Ptr+PtrOffset in RepPtr's /// block, then ReplaceAllUsesWith'ing everything. However, we would prefer to /// sink PtrOffset into user blocks where doing so will likely allow us to fold /// the constant add into a load or store instruction. Additionally, if a user /// is a pointer-pointer cast, we look through it to find its users. static void ReplaceUsesOfGEPInst(Instruction *RepPtr, Value *Ptr, Constant *PtrOffset, BasicBlock *DefBB, GetElementPtrInst *GEPI, std::map &InsertedExprs) { while (!RepPtr->use_empty()) { Instruction *User = cast(RepPtr->use_back()); // If the user is a Pointer-Pointer cast, recurse. Only BitCast can be // used for a Pointer-Pointer cast. if (isa(User)) { ReplaceUsesOfGEPInst(User, Ptr, PtrOffset, DefBB, GEPI, InsertedExprs); // Drop the use of RepPtr. The cast is dead. Don't delete it now, else we // could invalidate an iterator. User->setOperand(0, UndefValue::get(RepPtr->getType())); continue; } // If this is a load of the pointer, or a store through the pointer, emit // the increment into the load/store block. Instruction *NewVal; if (isa(User) || (isa(User) && User->getOperand(0) != RepPtr)) { NewVal = InsertGEPComputeCode(InsertedExprs[User->getParent()], User->getParent(), GEPI, Ptr, PtrOffset); } else { // If this use is not foldable into the addressing mode, use a version // emitted in the GEP block. NewVal = InsertGEPComputeCode(InsertedExprs[DefBB], DefBB, GEPI, Ptr, PtrOffset); } if (GEPI->getType() != RepPtr->getType()) { BasicBlock::iterator IP = NewVal; ++IP; // NewVal must be a GEP which must be pointer type, so BitCast NewVal = new BitCastInst(NewVal, RepPtr->getType(), "", IP); } User->replaceUsesOfWith(RepPtr, NewVal); } } /// OptimizeGEPExpression - Since we are doing basic-block-at-a-time instruction /// selection, we want to be a bit careful about some things. In particular, if /// we have a GEP instruction that is used in a different block than it is /// defined, the addressing expression of the GEP cannot be folded into loads or /// stores that use it. In this case, decompose the GEP and move constant /// indices into blocks that use it. bool CodeGenPrepare::OptimizeGEPExpression(GetElementPtrInst *GEPI) { // If this GEP is only used inside the block it is defined in, there is no // need to rewrite it. bool isUsedOutsideDefBB = false; BasicBlock *DefBB = GEPI->getParent(); for (Value::use_iterator UI = GEPI->use_begin(), E = GEPI->use_end(); UI != E; ++UI) { if (cast(*UI)->getParent() != DefBB) { isUsedOutsideDefBB = true; break; } } if (!isUsedOutsideDefBB) return false; // If this GEP has no non-zero constant indices, there is nothing we can do, // ignore it. bool hasConstantIndex = false; bool hasVariableIndex = false; for (GetElementPtrInst::op_iterator OI = GEPI->op_begin()+1, E = GEPI->op_end(); OI != E; ++OI) { if (ConstantInt *CI = dyn_cast(*OI)) { if (!CI->isZero()) { hasConstantIndex = true; break; } } else { hasVariableIndex = true; } } // If this is a "GEP X, 0, 0, 0", turn this into a cast. if (!hasConstantIndex && !hasVariableIndex) { /// The GEP operand must be a pointer, so must its result -> BitCast Value *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(), GEPI->getName(), GEPI); GEPI->replaceAllUsesWith(NC); GEPI->eraseFromParent(); return true; } // If this is a GEP &Alloca, 0, 0, forward subst the frame index into uses. if (!hasConstantIndex && !isa(GEPI->getOperand(0))) return false; // If we don't have target lowering info, we can't lower the GEP. if (!TLI) return false; const TargetData *TD = TLI->getTargetData(); // Otherwise, decompose the GEP instruction into multiplies and adds. Sum the // constant offset (which we now know is non-zero) and deal with it later. uint64_t ConstantOffset = 0; const Type *UIntPtrTy = TD->getIntPtrType(); Value *Ptr = new PtrToIntInst(GEPI->getOperand(0), UIntPtrTy, "", GEPI); const Type *Ty = GEPI->getOperand(0)->getType(); for (GetElementPtrInst::op_iterator OI = GEPI->op_begin()+1, E = GEPI->op_end(); OI != E; ++OI) { Value *Idx = *OI; if (const StructType *StTy = dyn_cast(Ty)) { unsigned Field = cast(Idx)->getZExtValue(); if (Field) ConstantOffset += TD->getStructLayout(StTy)->getElementOffset(Field); Ty = StTy->getElementType(Field); } else { Ty = cast(Ty)->getElementType(); // Handle constant subscripts. if (ConstantInt *CI = dyn_cast(Idx)) { if (CI->getZExtValue() == 0) continue; ConstantOffset += (int64_t)TD->getTypeSize(Ty)*CI->getSExtValue(); continue; } // Ptr = Ptr + Idx * ElementSize; // Cast Idx to UIntPtrTy if needed. Idx = CastInst::createIntegerCast(Idx, UIntPtrTy, true/*SExt*/, "", GEPI); uint64_t ElementSize = TD->getTypeSize(Ty); // Mask off bits that should not be set. ElementSize &= ~0ULL >> (64-UIntPtrTy->getPrimitiveSizeInBits()); Constant *SizeCst = ConstantInt::get(UIntPtrTy, ElementSize); // Multiply by the element size and add to the base. Idx = BinaryOperator::createMul(Idx, SizeCst, "", GEPI); Ptr = BinaryOperator::createAdd(Ptr, Idx, "", GEPI); } } // Make sure that the offset fits in uintptr_t. ConstantOffset &= ~0ULL >> (64-UIntPtrTy->getPrimitiveSizeInBits()); Constant *PtrOffset = ConstantInt::get(UIntPtrTy, ConstantOffset); // Okay, we have now emitted all of the variable index parts to the BB that // the GEP is defined in. Loop over all of the using instructions, inserting // an "add Ptr, ConstantOffset" into each block that uses it and update the // instruction to use the newly computed value, making GEPI dead. When the // user is a load or store instruction address, we emit the add into the user // block, otherwise we use a canonical version right next to the gep (these // won't be foldable as addresses, so we might as well share the computation). std::map InsertedExprs; ReplaceUsesOfGEPInst(GEPI, Ptr, PtrOffset, DefBB, GEPI, InsertedExprs); // Finally, the GEP is dead, remove it. GEPI->eraseFromParent(); return true; } /// SinkInvariantGEPIndex - If a GEP instruction has a variable index that has /// been hoisted out of the loop by LICM pass, sink it back into the use BB /// if it can be determined that the index computation can be folded into the /// addressing mode of the load / store uses. static bool SinkInvariantGEPIndex(BinaryOperator *BinOp, const TargetLowering &TLI) { // Only look at Add. if (BinOp->getOpcode() != Instruction::Add) return false; // DestBBs - These are the blocks where a copy of BinOp will be inserted. SmallSet DestBBs; BasicBlock *DefBB = BinOp->getParent(); bool MadeChange = false; for (Value::use_iterator UI = BinOp->use_begin(), E = BinOp->use_end(); UI != E; ++UI) { Instruction *GEPI = cast(*UI); // Only look for GEP use in another block. if (GEPI->getParent() == DefBB) continue; if (isa(GEPI)) { // If the GEP has another variable index, abondon. bool hasVariableIndex = false; for (GetElementPtrInst::op_iterator OI = GEPI->op_begin()+1, OE = GEPI->op_end(); OI != OE; ++OI) if (*OI != BinOp && !isa(*OI)) { hasVariableIndex = true; break; } if (hasVariableIndex) break; BasicBlock *GEPIBB = GEPI->getParent(); for (Value::use_iterator UUI = GEPI->use_begin(), UE = GEPI->use_end(); UUI != UE; ++UUI) { Instruction *GEPIUser = cast(*UUI); const Type *UseTy = NULL; if (LoadInst *Load = dyn_cast(GEPIUser)) UseTy = Load->getType(); else if (StoreInst *Store = dyn_cast(GEPIUser)) UseTy = Store->getOperand(0)->getType(); // Check if it is possible to fold the expression to address mode. if (UseTy && isa(BinOp->getOperand(1))) { int64_t Cst = cast(BinOp->getOperand(1))->getSExtValue(); // e.g. load (gep i32 * %P, (X+42)) => load (%P + X*4 + 168). TargetLowering::AddrMode AM; // FIXME: This computation isn't right, scale is incorrect. AM.Scale = TLI.getTargetData()->getTypeSize(UseTy); // FIXME: Should should also include other fixed offsets. AM.BaseOffs = Cst*AM.Scale; if (TLI.isLegalAddressingMode(AM, UseTy)) { DestBBs.insert(GEPIBB); MadeChange = true; break; } } } } } // Nothing to do. if (!MadeChange) return false; /// InsertedOps - Only insert a duplicate in each block once. std::map InsertedOps; for (Value::use_iterator UI = BinOp->use_begin(), E = BinOp->use_end(); UI != E; ) { Instruction *User = cast(*UI); BasicBlock *UserBB = User->getParent(); // Preincrement use iterator so we don't invalidate it. ++UI; // If any user in this BB wants it, replace all the uses in the BB. if (DestBBs.count(UserBB)) { // Sink it into user block. BinaryOperator *&InsertedOp = InsertedOps[UserBB]; if (!InsertedOp) { BasicBlock::iterator InsertPt = UserBB->begin(); while (isa(InsertPt)) ++InsertPt; InsertedOp = BinaryOperator::create(BinOp->getOpcode(), BinOp->getOperand(0), BinOp->getOperand(1), "", InsertPt); } User->replaceUsesOfWith(BinOp, InsertedOp); } } if (BinOp->use_empty()) BinOp->eraseFromParent(); return true; } /// OptimizeNoopCopyExpression - We have determined that the specified cast /// instruction is a noop copy (e.g. it's casting from one pointer type to /// another, int->uint, or int->sbyte on PPC. /// /// Return true if any changes are made. static bool OptimizeNoopCopyExpression(CastInst *CI) { BasicBlock *DefBB = CI->getParent(); /// InsertedCasts - Only insert a cast in each block once. std::map InsertedCasts; bool MadeChange = false; for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); UI != E; ) { Use &TheUse = UI.getUse(); Instruction *User = cast(*UI); // Figure out which BB this cast is used in. For PHI's this is the // appropriate predecessor block. BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast(User)) { unsigned OpVal = UI.getOperandNo()/2; UserBB = PN->getIncomingBlock(OpVal); } // Preincrement use iterator so we don't invalidate it. ++UI; // If this user is in the same block as the cast, don't change the cast. if (UserBB == DefBB) continue; // If we have already inserted a cast into this block, use it. CastInst *&InsertedCast = InsertedCasts[UserBB]; if (!InsertedCast) { BasicBlock::iterator InsertPt = UserBB->begin(); while (isa(InsertPt)) ++InsertPt; InsertedCast = CastInst::create(CI->getOpcode(), CI->getOperand(0), CI->getType(), "", InsertPt); MadeChange = true; } // Replace a use of the cast with a use of the new casat. TheUse = InsertedCast; } // If we removed all uses, nuke the cast. if (CI->use_empty()) CI->eraseFromParent(); return MadeChange; } // In this pass we look for GEP and cast instructions that are used // across basic blocks and rewrite them to improve basic-block-at-a-time // selection. bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) { bool MadeChange = false; // Split all critical edges where the dest block has a PHI and where the phi // has shared immediate operands. TerminatorInst *BBTI = BB.getTerminator(); if (BBTI->getNumSuccessors() > 1) { for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) if (isa(BBTI->getSuccessor(i)->begin()) && isCriticalEdge(BBTI, i, true)) SplitEdgeNicely(BBTI, i, this); } for (BasicBlock::iterator BBI = BB.begin(), E = BB.end(); BBI != E; ) { Instruction *I = BBI++; if (CallInst *CI = dyn_cast(I)) { // If we found an inline asm expession, and if the target knows how to // lower it to normal LLVM code, do so now. if (TLI && isa(CI->getCalledValue())) if (const TargetAsmInfo *TAI = TLI->getTargetMachine().getTargetAsmInfo()) { if (TAI->ExpandInlineAsm(CI)) BBI = BB.begin(); } } else if (GetElementPtrInst *GEPI = dyn_cast(I)) { MadeChange |= OptimizeGEPExpression(GEPI); } else if (CastInst *CI = dyn_cast(I)) { // If the source of the cast is a constant, then this should have // already been constant folded. The only reason NOT to constant fold // it is if something (e.g. LSR) was careful to place the constant // evaluation in a block other than then one that uses it (e.g. to hoist // the address of globals out of a loop). If this is the case, we don't // want to forward-subst the cast. if (isa(CI->getOperand(0))) continue; if (!TLI) continue; // If this is a noop copy, sink it into user blocks to reduce the number // of virtual registers that must be created and coallesced. MVT::ValueType SrcVT = TLI->getValueType(CI->getOperand(0)->getType()); MVT::ValueType DstVT = TLI->getValueType(CI->getType()); // This is an fp<->int conversion? if (MVT::isInteger(SrcVT) != MVT::isInteger(DstVT)) continue; // If this is an extension, it will be a zero or sign extension, which // isn't a noop. if (SrcVT < DstVT) continue; // If these values will be promoted, find out what they will be promoted // to. This helps us consider truncates on PPC as noop copies when they // are. if (TLI->getTypeAction(SrcVT) == TargetLowering::Promote) SrcVT = TLI->getTypeToTransformTo(SrcVT); if (TLI->getTypeAction(DstVT) == TargetLowering::Promote) DstVT = TLI->getTypeToTransformTo(DstVT); // If, after promotion, these are the same types, this is a noop copy. if (SrcVT == DstVT) MadeChange |= OptimizeNoopCopyExpression(CI); } else if (BinaryOperator *BinOp = dyn_cast(I)) { if (TLI) MadeChange |= SinkInvariantGEPIndex(BinOp, *TLI); } } return MadeChange; }