/// DoPromotion - This method actually performs the promotion of the specified /// arguments, and returns the new function. At this point, we know that it's /// safe to do so. CallGraphNode *ArgPromotion::DoPromotion(Function *F, SmallPtrSet<Argument*, 8> &ArgsToPromote, SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { // Start by computing a new prototype for the function, which is the same as // the old function, but has modified arguments. const FunctionType *FTy = F->getFunctionType(); std::vector<const Type*> Params; typedef std::set<IndicesVector> ScalarizeTable; // ScalarizedElements - If we are promoting a pointer that has elements // accessed out of it, keep track of which elements are accessed so that we // can add one argument for each. // // Arguments that are directly loaded will have a zero element value here, to // handle cases where there are both a direct load and GEP accesses. // std::map<Argument*, ScalarizeTable> ScalarizedElements; // OriginalLoads - Keep track of a representative load instruction from the // original function so that we can tell the alias analysis implementation // what the new GEP/Load instructions we are inserting look like. std::map<IndicesVector, LoadInst*> OriginalLoads; // Attributes - Keep track of the parameter attributes for the arguments // that we are *not* promoting. For the ones that we do promote, the parameter // attributes are lost SmallVector<AttributeWithIndex, 8> AttributesVec; const AttrListPtr &PAL = F->getAttributes(); // Add any return attributes. if (Attributes attrs = PAL.getRetAttributes()) AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); // First, determine the new argument list unsigned ArgIndex = 1; for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I, ++ArgIndex) { if (ByValArgsToTransform.count(I)) { // Simple byval argument? Just add all the struct element types. const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); const StructType *STy = cast<StructType>(AgTy); for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) Params.push_back(STy->getElementType(i)); ++NumByValArgsPromoted; } else if (!ArgsToPromote.count(I)) { // Unchanged argument Params.push_back(I->getType()); if (Attributes attrs = PAL.getParamAttributes(ArgIndex)) AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); } else if (I->use_empty()) { // Dead argument (which are always marked as promotable) ++NumArgumentsDead; } else { // Okay, this is being promoted. This means that the only uses are loads // or GEPs which are only used by loads // In this table, we will track which indices are loaded from the argument // (where direct loads are tracked as no indices). ScalarizeTable &ArgIndices = ScalarizedElements[I]; for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; ++UI) { Instruction *User = cast<Instruction>(*UI); assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); IndicesVector Indices; Indices.reserve(User->getNumOperands() - 1); // Since loads will only have a single operand, and GEPs only a single // non-index operand, this will record direct loads without any indices, // and gep+loads with the GEP indices. for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); II != IE; ++II) Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); // GEPs with a single 0 index can be merged with direct loads if (Indices.size() == 1 && Indices.front() == 0) Indices.clear(); ArgIndices.insert(Indices); LoadInst *OrigLoad; if (LoadInst *L = dyn_cast<LoadInst>(User)) OrigLoad = L; else // Take any load, we will use it only to update Alias Analysis OrigLoad = cast<LoadInst>(User->use_back()); OriginalLoads[Indices] = OrigLoad; } // Add a parameter to the function for each element passed in. for (ScalarizeTable::iterator SI = ArgIndices.begin(), E = ArgIndices.end(); SI != E; ++SI) { // not allowed to dereference ->begin() if size() is 0 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), SI->begin(), SI->end())); assert(Params.back()); } if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) ++NumArgumentsPromoted; else ++NumAggregatesPromoted; } } // Add any function attributes. if (Attributes attrs = PAL.getFnAttributes()) AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); const Type *RetTy = FTy->getReturnType(); // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which // have zero fixed arguments. bool ExtraArgHack = false; if (Params.empty() && FTy->isVarArg()) { ExtraArgHack = true; Params.push_back(Type::getInt32Ty(F->getContext())); } // Construct the new function type using the new arguments. FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); // Create the new function body and insert it into the module. Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); NF->copyAttributesFrom(F); DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" << "From: " << *F); // Recompute the parameter attributes list based on the new arguments for // the function. NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end())); AttributesVec.clear(); F->getParent()->getFunctionList().insert(F, NF); NF->takeName(F); // Get the alias analysis information that we need to update to reflect our // changes. AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); // Get the callgraph information that we need to update to reflect our // changes. CallGraph &CG = getAnalysis<CallGraph>(); // Get a new callgraph node for NF. CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); // Loop over all of the callers of the function, transforming the call sites // to pass in the loaded pointers. // SmallVector<Value*, 16> Args; while (!F->use_empty()) { CallSite CS = CallSite::get(F->use_back()); assert(CS.getCalledFunction() == F); Instruction *Call = CS.getInstruction(); const AttrListPtr &CallPAL = CS.getAttributes(); // Add any return attributes. if (Attributes attrs = CallPAL.getRetAttributes()) AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); // Loop over the operands, inserting GEP and loads in the caller as // appropriate. CallSite::arg_iterator AI = CS.arg_begin(); ArgIndex = 1; for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I, ++AI, ++ArgIndex) if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { Args.push_back(*AI); // Unmodified argument if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); } else if (ByValArgsToTransform.count(I)) { // Emit a GEP and load for each element of the struct. const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); const StructType *STy = cast<StructType>(AgTy); Value *Idxs[2] = { ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, (*AI)->getName()+"."+utostr(i), Call); // TODO: Tell AA about the new values? Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); } } else if (!I->use_empty()) { // Non-dead argument: insert GEPs and loads as appropriate. ScalarizeTable &ArgIndices = ScalarizedElements[I]; // Store the Value* version of the indices in here, but declare it now // for reuse. std::vector<Value*> Ops; for (ScalarizeTable::iterator SI = ArgIndices.begin(), E = ArgIndices.end(); SI != E; ++SI) { Value *V = *AI; LoadInst *OrigLoad = OriginalLoads[*SI]; if (!SI->empty()) { Ops.reserve(SI->size()); const Type *ElTy = V->getType(); for (IndicesVector::const_iterator II = SI->begin(), IE = SI->end(); II != IE; ++II) { // Use i32 to index structs, and i64 for others (pointers/arrays). // This satisfies GEP constraints. const Type *IdxTy = (ElTy->isStructTy() ? Type::getInt32Ty(F->getContext()) : Type::getInt64Ty(F->getContext())); Ops.push_back(ConstantInt::get(IdxTy, *II)); // Keep track of the type we're currently indexing. ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); } // And create a GEP to extract those indices. V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), V->getName()+".idx", Call); Ops.clear(); AA.copyValue(OrigLoad->getOperand(0), V); } // Since we're replacing a load make sure we take the alignment // of the previous load. LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call); newLoad->setAlignment(OrigLoad->getAlignment()); Args.push_back(newLoad); AA.copyValue(OrigLoad, Args.back()); } } if (ExtraArgHack) Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); // Push any varargs arguments on the list. for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { Args.push_back(*AI); if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); } // Add any function attributes. if (Attributes attrs = CallPAL.getFnAttributes()) AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); Instruction *New; if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), Args.begin(), Args.end(), "", Call); cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end())); } else { New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end())); if (cast<CallInst>(Call)->isTailCall()) cast<CallInst>(New)->setTailCall(); } Args.clear(); AttributesVec.clear(); // Update the alias analysis implementation to know that we are replacing // the old call with a new one. AA.replaceWithNewValue(Call, New); // Update the callgraph to know that the callsite has been transformed. CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; CalleeNode->replaceCallEdge(Call, New, NF_CGN); if (!Call->use_empty()) { Call->replaceAllUsesWith(New); New->takeName(Call); } // Finally, remove the old call from the program, reducing the use-count of // F. Call->eraseFromParent(); } // Since we have now created the new function, splice the body of the old // function right into the new function, leaving the old rotting hulk of the // function empty. NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); // Loop over the argument list, transfering uses of the old arguments over to // the new arguments, also transfering over the names as well. // for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), I2 = NF->arg_begin(); I != E; ++I) { if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { // If this is an unmodified argument, move the name and users over to the // new version. I->replaceAllUsesWith(I2); I2->takeName(I); AA.replaceWithNewValue(I, I2); ++I2; continue; } if (ByValArgsToTransform.count(I)) { // In the callee, we create an alloca, and store each of the new incoming // arguments into the alloca. Instruction *InsertPt = NF->begin()->begin(); // Just add all the struct element types. const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); const StructType *STy = cast<StructType>(AgTy); Value *Idxs[2] = { ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); Value *Idx = GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, TheAlloca->getName()+"."+Twine(i), InsertPt); I2->setName(I->getName()+"."+Twine(i)); new StoreInst(I2++, Idx, InsertPt); } // Anything that used the arg should now use the alloca. I->replaceAllUsesWith(TheAlloca); TheAlloca->takeName(I); AA.replaceWithNewValue(I, TheAlloca); continue; } if (I->use_empty()) { AA.deleteValue(I); continue; } // Otherwise, if we promoted this argument, then all users are load // instructions (or GEPs with only load users), and all loads should be // using the new argument that we added. ScalarizeTable &ArgIndices = ScalarizedElements[I]; while (!I->use_empty()) { if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { assert(ArgIndices.begin()->empty() && "Load element should sort to front!"); I2->setName(I->getName()+".val"); LI->replaceAllUsesWith(I2); AA.replaceWithNewValue(LI, I2); LI->eraseFromParent(); DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() << "' in function '" << F->getName() << "'\n"); } else { GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); IndicesVector Operands; Operands.reserve(GEP->getNumIndices()); for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); II != IE; ++II) Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); // GEPs with a single 0 index can be merged with direct loads if (Operands.size() == 1 && Operands.front() == 0) Operands.clear(); Function::arg_iterator TheArg = I2; for (ScalarizeTable::iterator It = ArgIndices.begin(); *It != Operands; ++It, ++TheArg) { assert(It != ArgIndices.end() && "GEP not handled??"); } std::string NewName = I->getName(); for (unsigned i = 0, e = Operands.size(); i != e; ++i) { NewName += "." + utostr(Operands[i]); } NewName += ".val"; TheArg->setName(NewName); DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() << "' of function '" << NF->getName() << "'\n"); // All of the uses must be load instructions. Replace them all with // the argument specified by ArgNo. while (!GEP->use_empty()) { LoadInst *L = cast<LoadInst>(GEP->use_back()); L->replaceAllUsesWith(TheArg); AA.replaceWithNewValue(L, TheArg); L->eraseFromParent(); } AA.deleteValue(GEP); GEP->eraseFromParent(); } } // Increment I2 past all of the arguments added for this promoted pointer. for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) ++I2; } // Notify the alias analysis implementation that we inserted a new argument. if (ExtraArgHack) AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), NF->arg_begin()); // Tell the alias analysis that the old function is about to disappear. AA.replaceWithNewValue(F, NF); NF_CGN->stealCalledFunctionsFrom(CG[F]); // Now that the old function is dead, delete it. If there is a dangling // reference to the CallgraphNode, just leave the dead function around for // someone else to nuke. CallGraphNode *CGN = CG[F]; if (CGN->getNumReferences() == 0) delete CG.removeFunctionFromModule(CGN); else F->setLinkage(Function::ExternalLinkage); return NF_CGN; }
/// isSafeToPromoteArgument - As you might guess from the name of this method, /// it checks to see if it is both safe and useful to promote the argument. /// This method limits promotion of aggregates to only promote up to three /// elements of the aggregate in order to avoid exploding the number of /// arguments passed in. static bool isSafeToPromoteArgument(Argument *Arg, bool isByValOrInAlloca, AAResults &AAR, unsigned MaxElements) { typedef std::set<IndicesVector> GEPIndicesSet; // Quick exit for unused arguments if (Arg->use_empty()) return true; // We can only promote this argument if all of the uses are loads, or are GEP // instructions (with constant indices) that are subsequently loaded. // // Promoting the argument causes it to be loaded in the caller // unconditionally. This is only safe if we can prove that either the load // would have happened in the callee anyway (ie, there is a load in the entry // block) or the pointer passed in at every call site is guaranteed to be // valid. // In the former case, invalid loads can happen, but would have happened // anyway, in the latter case, invalid loads won't happen. This prevents us // from introducing an invalid load that wouldn't have happened in the // original code. // // This set will contain all sets of indices that are loaded in the entry // block, and thus are safe to unconditionally load in the caller. // // This optimization is also safe for InAlloca parameters, because it verifies // that the address isn't captured. GEPIndicesSet SafeToUnconditionallyLoad; // This set contains all the sets of indices that we are planning to promote. // This makes it possible to limit the number of arguments added. GEPIndicesSet ToPromote; // If the pointer is always valid, any load with first index 0 is valid. if (isByValOrInAlloca || AllCallersPassInValidPointerForArgument(Arg)) SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); // First, iterate the entry block and mark loads of (geps of) arguments as // safe. BasicBlock &EntryBlock = Arg->getParent()->front(); // Declare this here so we can reuse it IndicesVector Indices; for (Instruction &I : EntryBlock) if (LoadInst *LI = dyn_cast<LoadInst>(&I)) { Value *V = LI->getPointerOperand(); if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { V = GEP->getPointerOperand(); if (V == Arg) { // This load actually loads (part of) Arg? Check the indices then. Indices.reserve(GEP->getNumIndices()); for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); II != IE; ++II) if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) Indices.push_back(CI->getSExtValue()); else // We found a non-constant GEP index for this argument? Bail out // right away, can't promote this argument at all. return false; // Indices checked out, mark them as safe MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); Indices.clear(); } } else if (V == Arg) { // Direct loads are equivalent to a GEP with a single 0 index. MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); } } // Now, iterate all uses of the argument to see if there are any uses that are // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. SmallVector<LoadInst*, 16> Loads; IndicesVector Operands; for (Use &U : Arg->uses()) { User *UR = U.getUser(); Operands.clear(); if (LoadInst *LI = dyn_cast<LoadInst>(UR)) { // Don't hack volatile/atomic loads if (!LI->isSimple()) return false; Loads.push_back(LI); // Direct loads are equivalent to a GEP with a zero index and then a load. Operands.push_back(0); } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) { if (GEP->use_empty()) { // Dead GEP's cause trouble later. Just remove them if we run into // them. GEP->eraseFromParent(); // TODO: This runs the above loop over and over again for dead GEPs // Couldn't we just do increment the UI iterator earlier and erase the // use? return isSafeToPromoteArgument(Arg, isByValOrInAlloca, AAR, MaxElements); } // Ensure that all of the indices are constants. for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); i != e; ++i) if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) Operands.push_back(C->getSExtValue()); else return false; // Not a constant operand GEP! // Ensure that the only users of the GEP are load instructions. for (User *GEPU : GEP->users()) if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) { // Don't hack volatile/atomic loads if (!LI->isSimple()) return false; Loads.push_back(LI); } else { // Other uses than load? return false; } } else { return false; // Not a load or a GEP. } // Now, see if it is safe to promote this load / loads of this GEP. Loading // is safe if Operands, or a prefix of Operands, is marked as safe. if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) return false; // See if we are already promoting a load with these indices. If not, check // to make sure that we aren't promoting too many elements. If so, nothing // to do. if (ToPromote.find(Operands) == ToPromote.end()) { if (MaxElements > 0 && ToPromote.size() == MaxElements) { DEBUG(dbgs() << "argpromotion not promoting argument '" << Arg->getName() << "' because it would require adding more " << "than " << MaxElements << " arguments to the function.\n"); // We limit aggregate promotion to only promoting up to a fixed number // of elements of the aggregate. return false; } ToPromote.insert(std::move(Operands)); } } if (Loads.empty()) return true; // No users, this is a dead argument. // Okay, now we know that the argument is only used by load instructions and // it is safe to unconditionally perform all of them. Use alias analysis to // check to see if the pointer is guaranteed to not be modified from entry of // the function to each of the load instructions. // Because there could be several/many load instructions, remember which // blocks we know to be transparent to the load. df_iterator_default_set<BasicBlock*, 16> TranspBlocks; for (LoadInst *Load : Loads) { // Check to see if the load is invalidated from the start of the block to // the load itself. BasicBlock *BB = Load->getParent(); MemoryLocation Loc = MemoryLocation::get(Load); if (AAR.canInstructionRangeModRef(BB->front(), *Load, Loc, MRI_Mod)) return false; // Pointer is invalidated! // Now check every path from the entry block to the load for transparency. // To do this, we perform a depth first search on the inverse CFG from the // loading block. for (BasicBlock *P : predecessors(BB)) { for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks)) if (AAR.canBasicBlockModify(*TranspBB, Loc)) return false; } } // If the path from the entry of the function to each load is free of // instructions that potentially invalidate the load, we can make the // transformation! return true; }
/// isSafeToPromoteArgument - As you might guess from the name of this method, /// it checks to see if it is both safe and useful to promote the argument. /// This method limits promotion of aggregates to only promote up to three /// elements of the aggregate in order to avoid exploding the number of /// arguments passed in. bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { typedef std::set<IndicesVector> GEPIndicesSet; // Quick exit for unused arguments if (Arg->use_empty()) return true; // We can only promote this argument if all of the uses are loads, or are GEP // instructions (with constant indices) that are subsequently loaded. // // Promoting the argument causes it to be loaded in the caller // unconditionally. This is only safe if we can prove that either the load // would have happened in the callee anyway (ie, there is a load in the entry // block) or the pointer passed in at every call site is guaranteed to be // valid. // In the former case, invalid loads can happen, but would have happened // anyway, in the latter case, invalid loads won't happen. This prevents us // from introducing an invalid load that wouldn't have happened in the // original code. // // This set will contain all sets of indices that are loaded in the entry // block, and thus are safe to unconditionally load in the caller. GEPIndicesSet SafeToUnconditionallyLoad; // This set contains all the sets of indices that we are planning to promote. // This makes it possible to limit the number of arguments added. GEPIndicesSet ToPromote; // If the pointer is always valid, any load with first index 0 is valid. if (isByVal || AllCalleesPassInValidPointerForArgument(Arg)) SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); // First, iterate the entry block and mark loads of (geps of) arguments as // safe. BasicBlock *EntryBlock = Arg->getParent()->begin(); // Declare this here so we can reuse it IndicesVector Indices; for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); I != E; ++I) if (LoadInst *LI = dyn_cast<LoadInst>(I)) { Value *V = LI->getPointerOperand(); if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { V = GEP->getPointerOperand(); if (V == Arg) { // This load actually loads (part of) Arg? Check the indices then. Indices.reserve(GEP->getNumIndices()); for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); II != IE; ++II) if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) Indices.push_back(CI->getSExtValue()); else // We found a non-constant GEP index for this argument? Bail out // right away, can't promote this argument at all. return false; // Indices checked out, mark them as safe MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); Indices.clear(); } } else if (V == Arg) { // Direct loads are equivalent to a GEP with a single 0 index. MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); } } // Now, iterate all uses of the argument to see if there are any uses that are // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. SmallVector<LoadInst*, 16> Loads; IndicesVector Operands; for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); UI != E; ++UI) { User *U = *UI; Operands.clear(); if (LoadInst *LI = dyn_cast<LoadInst>(U)) { if (LI->isVolatile()) return false; // Don't hack volatile loads Loads.push_back(LI); // Direct loads are equivalent to a GEP with a zero index and then a load. Operands.push_back(0); } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { if (GEP->use_empty()) { // Dead GEP's cause trouble later. Just remove them if we run into // them. getAnalysis<AliasAnalysis>().deleteValue(GEP); GEP->eraseFromParent(); // TODO: This runs the above loop over and over again for dead GEPs // Couldn't we just do increment the UI iterator earlier and erase the // use? return isSafeToPromoteArgument(Arg, isByVal); } // Ensure that all of the indices are constants. for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); i != e; ++i) if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) Operands.push_back(C->getSExtValue()); else return false; // Not a constant operand GEP! // Ensure that the only users of the GEP are load instructions. for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); UI != E; ++UI) if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { if (LI->isVolatile()) return false; // Don't hack volatile loads Loads.push_back(LI); } else { // Other uses than load? return false; } } else { return false; // Not a load or a GEP. } // Now, see if it is safe to promote this load / loads of this GEP. Loading // is safe if Operands, or a prefix of Operands, is marked as safe. if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) return false; // See if we are already promoting a load with these indices. If not, check // to make sure that we aren't promoting too many elements. If so, nothing // to do. if (ToPromote.find(Operands) == ToPromote.end()) { if (maxElements > 0 && ToPromote.size() == maxElements) { DEBUG(dbgs() << "argpromotion not promoting argument '" << Arg->getName() << "' because it would require adding more " << "than " << maxElements << " arguments to the function.\n"); // We limit aggregate promotion to only promoting up to a fixed number // of elements of the aggregate. return false; } ToPromote.insert(Operands); } } if (Loads.empty()) return true; // No users, this is a dead argument. // Okay, now we know that the argument is only used by load instructions and // it is safe to unconditionally perform all of them. Use alias analysis to // check to see if the pointer is guaranteed to not be modified from entry of // the function to each of the load instructions. // Because there could be several/many load instructions, remember which // blocks we know to be transparent to the load. SmallPtrSet<BasicBlock*, 16> TranspBlocks; AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); TargetData *TD = getAnalysisIfAvailable<TargetData>(); if (!TD) return false; // Without TargetData, assume the worst. for (unsigned i = 0, e = Loads.size(); i != e; ++i) { // Check to see if the load is invalidated from the start of the block to // the load itself. LoadInst *Load = Loads[i]; BasicBlock *BB = Load->getParent(); const PointerType *LoadTy = cast<PointerType>(Load->getPointerOperand()->getType()); unsigned LoadSize =(unsigned)TD->getTypeStoreSize(LoadTy->getElementType()); if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) return false; // Pointer is invalidated! // Now check every path from the entry block to the load for transparency. // To do this, we perform a depth first search on the inverse CFG from the // loading block. for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { BasicBlock *P = *PI; for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > I = idf_ext_begin(P, TranspBlocks), E = idf_ext_end(P, TranspBlocks); I != E; ++I) if (AA.canBasicBlockModify(**I, Arg, LoadSize)) return false; } } // If the path from the entry of the function to each load is free of // instructions that potentially invalidate the load, we can make the // transformation! return true; }
/// DoPromotion - This method actually performs the promotion of the specified /// arguments, and returns the new function. At this point, we know that it's /// safe to do so. static Function * doPromotion(Function *F, SmallPtrSetImpl<Argument *> &ArgsToPromote, SmallPtrSetImpl<Argument *> &ByValArgsToTransform, Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>> ReplaceCallSite) { // Start by computing a new prototype for the function, which is the same as // the old function, but has modified arguments. FunctionType *FTy = F->getFunctionType(); std::vector<Type *> Params; using ScalarizeTable = std::set<std::pair<Type *, IndicesVector>>; // ScalarizedElements - If we are promoting a pointer that has elements // accessed out of it, keep track of which elements are accessed so that we // can add one argument for each. // // Arguments that are directly loaded will have a zero element value here, to // handle cases where there are both a direct load and GEP accesses. std::map<Argument *, ScalarizeTable> ScalarizedElements; // OriginalLoads - Keep track of a representative load instruction from the // original function so that we can tell the alias analysis implementation // what the new GEP/Load instructions we are inserting look like. // We need to keep the original loads for each argument and the elements // of the argument that are accessed. std::map<std::pair<Argument *, IndicesVector>, LoadInst *> OriginalLoads; // Attribute - Keep track of the parameter attributes for the arguments // that we are *not* promoting. For the ones that we do promote, the parameter // attributes are lost SmallVector<AttributeSet, 8> ArgAttrVec; AttributeList PAL = F->getAttributes(); // First, determine the new argument list unsigned ArgNo = 0; for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I, ++ArgNo) { if (ByValArgsToTransform.count(&*I)) { // Simple byval argument? Just add all the struct element types. Type *AgTy = cast<PointerType>(I->getType())->getElementType(); StructType *STy = cast<StructType>(AgTy); Params.insert(Params.end(), STy->element_begin(), STy->element_end()); ArgAttrVec.insert(ArgAttrVec.end(), STy->getNumElements(), AttributeSet()); ++NumByValArgsPromoted; } else if (!ArgsToPromote.count(&*I)) { // Unchanged argument Params.push_back(I->getType()); ArgAttrVec.push_back(PAL.getParamAttributes(ArgNo)); } else if (I->use_empty()) { // Dead argument (which are always marked as promotable) ++NumArgumentsDead; // There may be remaining metadata uses of the argument for things like // llvm.dbg.value. Replace them with undef. I->replaceAllUsesWith(UndefValue::get(I->getType())); } else { // Okay, this is being promoted. This means that the only uses are loads // or GEPs which are only used by loads // In this table, we will track which indices are loaded from the argument // (where direct loads are tracked as no indices). ScalarizeTable &ArgIndices = ScalarizedElements[&*I]; for (User *U : I->users()) { Instruction *UI = cast<Instruction>(U); Type *SrcTy; if (LoadInst *L = dyn_cast<LoadInst>(UI)) SrcTy = L->getType(); else SrcTy = cast<GetElementPtrInst>(UI)->getSourceElementType(); IndicesVector Indices; Indices.reserve(UI->getNumOperands() - 1); // Since loads will only have a single operand, and GEPs only a single // non-index operand, this will record direct loads without any indices, // and gep+loads with the GEP indices. for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end(); II != IE; ++II) Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); // GEPs with a single 0 index can be merged with direct loads if (Indices.size() == 1 && Indices.front() == 0) Indices.clear(); ArgIndices.insert(std::make_pair(SrcTy, Indices)); LoadInst *OrigLoad; if (LoadInst *L = dyn_cast<LoadInst>(UI)) OrigLoad = L; else // Take any load, we will use it only to update Alias Analysis OrigLoad = cast<LoadInst>(UI->user_back()); OriginalLoads[std::make_pair(&*I, Indices)] = OrigLoad; } // Add a parameter to the function for each element passed in. for (const auto &ArgIndex : ArgIndices) { // not allowed to dereference ->begin() if size() is 0 Params.push_back(GetElementPtrInst::getIndexedType( cast<PointerType>(I->getType()->getScalarType())->getElementType(), ArgIndex.second)); ArgAttrVec.push_back(AttributeSet()); assert(Params.back()); } if (ArgIndices.size() == 1 && ArgIndices.begin()->second.empty()) ++NumArgumentsPromoted; else ++NumAggregatesPromoted; } } Type *RetTy = FTy->getReturnType(); // Construct the new function type using the new arguments. FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); // Create the new function body and insert it into the module. Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); NF->copyAttributesFrom(F); // Patch the pointer to LLVM function in debug info descriptor. NF->setSubprogram(F->getSubprogram()); F->setSubprogram(nullptr); DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" << "From: " << *F); // Recompute the parameter attributes list based on the new arguments for // the function. NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttributes(), PAL.getRetAttributes(), ArgAttrVec)); ArgAttrVec.clear(); F->getParent()->getFunctionList().insert(F->getIterator(), NF); NF->takeName(F); // Loop over all of the callers of the function, transforming the call sites // to pass in the loaded pointers. // SmallVector<Value *, 16> Args; while (!F->use_empty()) { CallSite CS(F->user_back()); assert(CS.getCalledFunction() == F); Instruction *Call = CS.getInstruction(); const AttributeList &CallPAL = CS.getAttributes(); // Loop over the operands, inserting GEP and loads in the caller as // appropriate. CallSite::arg_iterator AI = CS.arg_begin(); ArgNo = 0; for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I, ++AI, ++ArgNo) if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) { Args.push_back(*AI); // Unmodified argument ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo)); } else if (ByValArgsToTransform.count(&*I)) { // Emit a GEP and load for each element of the struct. Type *AgTy = cast<PointerType>(I->getType())->getElementType(); StructType *STy = cast<StructType>(AgTy); Value *Idxs[2] = { ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr}; for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); Value *Idx = GetElementPtrInst::Create( STy, *AI, Idxs, (*AI)->getName() + "." + Twine(i), Call); // TODO: Tell AA about the new values? Args.push_back(new LoadInst(Idx, Idx->getName() + ".val", Call)); ArgAttrVec.push_back(AttributeSet()); } } else if (!I->use_empty()) { // Non-dead argument: insert GEPs and loads as appropriate. ScalarizeTable &ArgIndices = ScalarizedElements[&*I]; // Store the Value* version of the indices in here, but declare it now // for reuse. std::vector<Value *> Ops; for (const auto &ArgIndex : ArgIndices) { Value *V = *AI; LoadInst *OrigLoad = OriginalLoads[std::make_pair(&*I, ArgIndex.second)]; if (!ArgIndex.second.empty()) { Ops.reserve(ArgIndex.second.size()); Type *ElTy = V->getType(); for (auto II : ArgIndex.second) { // Use i32 to index structs, and i64 for others (pointers/arrays). // This satisfies GEP constraints. Type *IdxTy = (ElTy->isStructTy() ? Type::getInt32Ty(F->getContext()) : Type::getInt64Ty(F->getContext())); Ops.push_back(ConstantInt::get(IdxTy, II)); // Keep track of the type we're currently indexing. if (auto *ElPTy = dyn_cast<PointerType>(ElTy)) ElTy = ElPTy->getElementType(); else ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(II); } // And create a GEP to extract those indices. V = GetElementPtrInst::Create(ArgIndex.first, V, Ops, V->getName() + ".idx", Call); Ops.clear(); } // Since we're replacing a load make sure we take the alignment // of the previous load. LoadInst *newLoad = new LoadInst(V, V->getName() + ".val", Call); newLoad->setAlignment(OrigLoad->getAlignment()); // Transfer the AA info too. AAMDNodes AAInfo; OrigLoad->getAAMetadata(AAInfo); newLoad->setAAMetadata(AAInfo); Args.push_back(newLoad); ArgAttrVec.push_back(AttributeSet()); } } // Push any varargs arguments on the list. for (; AI != CS.arg_end(); ++AI, ++ArgNo) { Args.push_back(*AI); ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo)); } SmallVector<OperandBundleDef, 1> OpBundles; CS.getOperandBundlesAsDefs(OpBundles); CallSite NewCS; if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), Args, OpBundles, "", Call); } else { auto *NewCall = CallInst::Create(NF, Args, OpBundles, "", Call); NewCall->setTailCallKind(cast<CallInst>(Call)->getTailCallKind()); NewCS = NewCall; } NewCS.setCallingConv(CS.getCallingConv()); NewCS.setAttributes( AttributeList::get(F->getContext(), CallPAL.getFnAttributes(), CallPAL.getRetAttributes(), ArgAttrVec)); NewCS->setDebugLoc(Call->getDebugLoc()); uint64_t W; if (Call->extractProfTotalWeight(W)) NewCS->setProfWeight(W); Args.clear(); ArgAttrVec.clear(); // Update the callgraph to know that the callsite has been transformed. if (ReplaceCallSite) (*ReplaceCallSite)(CS, NewCS); if (!Call->use_empty()) { Call->replaceAllUsesWith(NewCS.getInstruction()); NewCS->takeName(Call); } // Finally, remove the old call from the program, reducing the use-count of // F. Call->eraseFromParent(); } const DataLayout &DL = F->getParent()->getDataLayout(); // Since we have now created the new function, splice the body of the old // function right into the new function, leaving the old rotting hulk of the // function empty. NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); // Loop over the argument list, transferring uses of the old arguments over to // the new arguments, also transferring over the names as well. for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), I2 = NF->arg_begin(); I != E; ++I) { if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) { // If this is an unmodified argument, move the name and users over to the // new version. I->replaceAllUsesWith(&*I2); I2->takeName(&*I); ++I2; continue; } if (ByValArgsToTransform.count(&*I)) { // In the callee, we create an alloca, and store each of the new incoming // arguments into the alloca. Instruction *InsertPt = &NF->begin()->front(); // Just add all the struct element types. Type *AgTy = cast<PointerType>(I->getType())->getElementType(); Value *TheAlloca = new AllocaInst(AgTy, DL.getAllocaAddrSpace(), nullptr, I->getParamAlignment(), "", InsertPt); StructType *STy = cast<StructType>(AgTy); Value *Idxs[2] = {ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr}; for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); Value *Idx = GetElementPtrInst::Create( AgTy, TheAlloca, Idxs, TheAlloca->getName() + "." + Twine(i), InsertPt); I2->setName(I->getName() + "." + Twine(i)); new StoreInst(&*I2++, Idx, InsertPt); } // Anything that used the arg should now use the alloca. I->replaceAllUsesWith(TheAlloca); TheAlloca->takeName(&*I); // If the alloca is used in a call, we must clear the tail flag since // the callee now uses an alloca from the caller. for (User *U : TheAlloca->users()) { CallInst *Call = dyn_cast<CallInst>(U); if (!Call) continue; Call->setTailCall(false); } continue; } if (I->use_empty()) continue; // Otherwise, if we promoted this argument, then all users are load // instructions (or GEPs with only load users), and all loads should be // using the new argument that we added. ScalarizeTable &ArgIndices = ScalarizedElements[&*I]; while (!I->use_empty()) { if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) { assert(ArgIndices.begin()->second.empty() && "Load element should sort to front!"); I2->setName(I->getName() + ".val"); LI->replaceAllUsesWith(&*I2); LI->eraseFromParent(); DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() << "' in function '" << F->getName() << "'\n"); } else { GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back()); IndicesVector Operands; Operands.reserve(GEP->getNumIndices()); for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); II != IE; ++II) Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); // GEPs with a single 0 index can be merged with direct loads if (Operands.size() == 1 && Operands.front() == 0) Operands.clear(); Function::arg_iterator TheArg = I2; for (ScalarizeTable::iterator It = ArgIndices.begin(); It->second != Operands; ++It, ++TheArg) { assert(It != ArgIndices.end() && "GEP not handled??"); } std::string NewName = I->getName(); for (unsigned i = 0, e = Operands.size(); i != e; ++i) { NewName += "." + utostr(Operands[i]); } NewName += ".val"; TheArg->setName(NewName); DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() << "' of function '" << NF->getName() << "'\n"); // All of the uses must be load instructions. Replace them all with // the argument specified by ArgNo. while (!GEP->use_empty()) { LoadInst *L = cast<LoadInst>(GEP->user_back()); L->replaceAllUsesWith(&*TheArg); L->eraseFromParent(); } GEP->eraseFromParent(); } } // Increment I2 past all of the arguments added for this promoted pointer. std::advance(I2, ArgIndices.size()); } return NF; }