| //===-- SwiftErrorValueTracking.cpp --------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This implements a limited mem2reg-like analysis to promote uses of function |
| // arguments and allocas marked with swiftalloc from memory into virtual |
| // registers tracked by this class. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/SwiftErrorValueTracking.h" |
| #include "llvm/ADT/PostOrderIterator.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/CodeGen/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetLowering.h" |
| #include "llvm/IR/Value.h" |
| |
| using namespace llvm; |
| |
| Register SwiftErrorValueTracking::getOrCreateVReg(const MachineBasicBlock *MBB, |
| const Value *Val) { |
| auto Key = std::make_pair(MBB, Val); |
| auto It = VRegDefMap.find(Key); |
| // If this is the first use of this swifterror value in this basic block, |
| // create a new virtual register. |
| // After we processed all basic blocks we will satisfy this "upwards exposed |
| // use" by inserting a copy or phi at the beginning of this block. |
| if (It == VRegDefMap.end()) { |
| auto &DL = MF->getDataLayout(); |
| const TargetRegisterClass *RC = TLI->getRegClassFor(TLI->getPointerTy(DL)); |
| auto VReg = MF->getRegInfo().createVirtualRegister(RC); |
| VRegDefMap[Key] = VReg; |
| VRegUpwardsUse[Key] = VReg; |
| return VReg; |
| } else |
| return It->second; |
| } |
| |
| void SwiftErrorValueTracking::setCurrentVReg(const MachineBasicBlock *MBB, |
| const Value *Val, Register VReg) { |
| VRegDefMap[std::make_pair(MBB, Val)] = VReg; |
| } |
| |
| Register SwiftErrorValueTracking::getOrCreateVRegDefAt( |
| const Instruction *I, const MachineBasicBlock *MBB, const Value *Val) { |
| auto Key = PointerIntPair<const Instruction *, 1, bool>(I, true); |
| auto It = VRegDefUses.find(Key); |
| if (It != VRegDefUses.end()) |
| return It->second; |
| |
| auto &DL = MF->getDataLayout(); |
| const TargetRegisterClass *RC = TLI->getRegClassFor(TLI->getPointerTy(DL)); |
| Register VReg = MF->getRegInfo().createVirtualRegister(RC); |
| VRegDefUses[Key] = VReg; |
| setCurrentVReg(MBB, Val, VReg); |
| return VReg; |
| } |
| |
| Register SwiftErrorValueTracking::getOrCreateVRegUseAt( |
| const Instruction *I, const MachineBasicBlock *MBB, const Value *Val) { |
| auto Key = PointerIntPair<const Instruction *, 1, bool>(I, false); |
| auto It = VRegDefUses.find(Key); |
| if (It != VRegDefUses.end()) |
| return It->second; |
| |
| Register VReg = getOrCreateVReg(MBB, Val); |
| VRegDefUses[Key] = VReg; |
| return VReg; |
| } |
| |
| /// Set up SwiftErrorVals by going through the function. If the function has |
| /// swifterror argument, it will be the first entry. |
| void SwiftErrorValueTracking::setFunction(MachineFunction &mf) { |
| MF = &mf; |
| Fn = &MF->getFunction(); |
| TLI = MF->getSubtarget().getTargetLowering(); |
| TII = MF->getSubtarget().getInstrInfo(); |
| |
| if (!TLI->supportSwiftError()) |
| return; |
| |
| SwiftErrorVals.clear(); |
| VRegDefMap.clear(); |
| VRegUpwardsUse.clear(); |
| VRegDefUses.clear(); |
| SwiftErrorArg = nullptr; |
| |
| // Check if function has a swifterror argument. |
| bool HaveSeenSwiftErrorArg = false; |
| for (Function::const_arg_iterator AI = Fn->arg_begin(), AE = Fn->arg_end(); |
| AI != AE; ++AI) |
| if (AI->hasSwiftErrorAttr()) { |
| assert(!HaveSeenSwiftErrorArg && |
| "Must have only one swifterror parameter"); |
| (void)HaveSeenSwiftErrorArg; // silence warning. |
| HaveSeenSwiftErrorArg = true; |
| SwiftErrorArg = &*AI; |
| SwiftErrorVals.push_back(&*AI); |
| } |
| |
| for (const auto &LLVMBB : *Fn) |
| for (const auto &Inst : LLVMBB) { |
| if (const AllocaInst *Alloca = dyn_cast<AllocaInst>(&Inst)) |
| if (Alloca->isSwiftError()) |
| SwiftErrorVals.push_back(Alloca); |
| } |
| } |
| |
| bool SwiftErrorValueTracking::createEntriesInEntryBlock(DebugLoc DbgLoc) { |
| if (!TLI->supportSwiftError()) |
| return false; |
| |
| // We only need to do this when we have swifterror parameter or swifterror |
| // alloc. |
| if (SwiftErrorVals.empty()) |
| return false; |
| |
| MachineBasicBlock *MBB = &*MF->begin(); |
| auto &DL = MF->getDataLayout(); |
| auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL)); |
| bool Inserted = false; |
| for (const auto *SwiftErrorVal : SwiftErrorVals) { |
| // We will always generate a copy from the argument. It is always used at |
| // least by the 'return' of the swifterror. |
| if (SwiftErrorArg && SwiftErrorArg == SwiftErrorVal) |
| continue; |
| Register VReg = MF->getRegInfo().createVirtualRegister(RC); |
| // Assign Undef to Vreg. We construct MI directly to make sure it works |
| // with FastISel. |
| BuildMI(*MBB, MBB->getFirstNonPHI(), DbgLoc, |
| TII->get(TargetOpcode::IMPLICIT_DEF), VReg); |
| |
| setCurrentVReg(MBB, SwiftErrorVal, VReg); |
| Inserted = true; |
| } |
| |
| return Inserted; |
| } |
| |
| /// Propagate swifterror values through the machine function CFG. |
| void SwiftErrorValueTracking::propagateVRegs() { |
| if (!TLI->supportSwiftError()) |
| return; |
| |
| // We only need to do this when we have swifterror parameter or swifterror |
| // alloc. |
| if (SwiftErrorVals.empty()) |
| return; |
| |
| // For each machine basic block in reverse post order. |
| ReversePostOrderTraversal<MachineFunction *> RPOT(MF); |
| for (MachineBasicBlock *MBB : RPOT) { |
| // For each swifterror value in the function. |
| for (const auto *SwiftErrorVal : SwiftErrorVals) { |
| auto Key = std::make_pair(MBB, SwiftErrorVal); |
| auto UUseIt = VRegUpwardsUse.find(Key); |
| auto VRegDefIt = VRegDefMap.find(Key); |
| bool UpwardsUse = UUseIt != VRegUpwardsUse.end(); |
| Register UUseVReg = UpwardsUse ? UUseIt->second : Register(); |
| bool DownwardDef = VRegDefIt != VRegDefMap.end(); |
| assert(!(UpwardsUse && !DownwardDef) && |
| "We can't have an upwards use but no downwards def"); |
| |
| // If there is no upwards exposed use and an entry for the swifterror in |
| // the def map for this value we don't need to do anything: We already |
| // have a downward def for this basic block. |
| if (!UpwardsUse && DownwardDef) |
| continue; |
| |
| // Otherwise we either have an upwards exposed use vreg that we need to |
| // materialize or need to forward the downward def from predecessors. |
| |
| // Check whether we have a single vreg def from all predecessors. |
| // Otherwise we need a phi. |
| SmallVector<std::pair<MachineBasicBlock *, Register>, 4> VRegs; |
| SmallSet<const MachineBasicBlock *, 8> Visited; |
| for (auto *Pred : MBB->predecessors()) { |
| if (!Visited.insert(Pred).second) |
| continue; |
| VRegs.push_back(std::make_pair( |
| Pred, getOrCreateVReg(Pred, SwiftErrorVal))); |
| if (Pred != MBB) |
| continue; |
| // We have a self-edge. |
| // If there was no upwards use in this basic block there is now one: the |
| // phi needs to use it self. |
| if (!UpwardsUse) { |
| UpwardsUse = true; |
| UUseIt = VRegUpwardsUse.find(Key); |
| assert(UUseIt != VRegUpwardsUse.end()); |
| UUseVReg = UUseIt->second; |
| } |
| } |
| |
| // We need a phi node if we have more than one predecessor with different |
| // downward defs. |
| bool needPHI = |
| VRegs.size() >= 1 && |
| llvm::any_of( |
| VRegs, |
| [&](const std::pair<const MachineBasicBlock *, Register> &V) |
| -> bool { return V.second != VRegs[0].second; }); |
| |
| // If there is no upwards exposed used and we don't need a phi just |
| // forward the swifterror vreg from the predecessor(s). |
| if (!UpwardsUse && !needPHI) { |
| assert(!VRegs.empty() && |
| "No predecessors? The entry block should bail out earlier"); |
| // Just forward the swifterror vreg from the predecessor(s). |
| setCurrentVReg(MBB, SwiftErrorVal, VRegs[0].second); |
| continue; |
| } |
| |
| auto DLoc = isa<Instruction>(SwiftErrorVal) |
| ? cast<Instruction>(SwiftErrorVal)->getDebugLoc() |
| : DebugLoc(); |
| const auto *TII = MF->getSubtarget().getInstrInfo(); |
| |
| // If we don't need a phi create a copy to the upward exposed vreg. |
| if (!needPHI) { |
| assert(UpwardsUse); |
| assert(!VRegs.empty() && |
| "No predecessors? Is the Calling Convention correct?"); |
| Register DestReg = UUseVReg; |
| BuildMI(*MBB, MBB->getFirstNonPHI(), DLoc, TII->get(TargetOpcode::COPY), |
| DestReg) |
| .addReg(VRegs[0].second); |
| continue; |
| } |
| |
| // We need a phi: if there is an upwards exposed use we already have a |
| // destination virtual register number otherwise we generate a new one. |
| auto &DL = MF->getDataLayout(); |
| auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL)); |
| Register PHIVReg = |
| UpwardsUse ? UUseVReg : MF->getRegInfo().createVirtualRegister(RC); |
| MachineInstrBuilder PHI = |
| BuildMI(*MBB, MBB->getFirstNonPHI(), DLoc, |
| TII->get(TargetOpcode::PHI), PHIVReg); |
| for (auto BBRegPair : VRegs) { |
| PHI.addReg(BBRegPair.second).addMBB(BBRegPair.first); |
| } |
| |
| // We did not have a definition in this block before: store the phi's vreg |
| // as this block downward exposed def. |
| if (!UpwardsUse) |
| setCurrentVReg(MBB, SwiftErrorVal, PHIVReg); |
| } |
| } |
| } |
| |
| void SwiftErrorValueTracking::preassignVRegs( |
| MachineBasicBlock *MBB, BasicBlock::const_iterator Begin, |
| BasicBlock::const_iterator End) { |
| if (!TLI->supportSwiftError() || SwiftErrorVals.empty()) |
| return; |
| |
| // Iterator over instructions and assign vregs to swifterror defs and uses. |
| for (auto It = Begin; It != End; ++It) { |
| if (auto *CB = dyn_cast<CallBase>(&*It)) { |
| // A call-site with a swifterror argument is both use and def. |
| const Value *SwiftErrorAddr = nullptr; |
| for (const auto &Arg : CB->args()) { |
| if (!Arg->isSwiftError()) |
| continue; |
| // Use of swifterror. |
| assert(!SwiftErrorAddr && "Cannot have multiple swifterror arguments"); |
| SwiftErrorAddr = &*Arg; |
| assert(SwiftErrorAddr->isSwiftError() && |
| "Must have a swifterror value argument"); |
| getOrCreateVRegUseAt(&*It, MBB, SwiftErrorAddr); |
| } |
| if (!SwiftErrorAddr) |
| continue; |
| |
| // Def of swifterror. |
| getOrCreateVRegDefAt(&*It, MBB, SwiftErrorAddr); |
| |
| // A load is a use. |
| } else if (const LoadInst *LI = dyn_cast<const LoadInst>(&*It)) { |
| const Value *V = LI->getOperand(0); |
| if (!V->isSwiftError()) |
| continue; |
| |
| getOrCreateVRegUseAt(LI, MBB, V); |
| |
| // A store is a def. |
| } else if (const StoreInst *SI = dyn_cast<const StoreInst>(&*It)) { |
| const Value *SwiftErrorAddr = SI->getOperand(1); |
| if (!SwiftErrorAddr->isSwiftError()) |
| continue; |
| |
| // Def of swifterror. |
| getOrCreateVRegDefAt(&*It, MBB, SwiftErrorAddr); |
| |
| // A return in a swiferror returning function is a use. |
| } else if (const ReturnInst *R = dyn_cast<const ReturnInst>(&*It)) { |
| const Function *F = R->getParent()->getParent(); |
| if (!F->getAttributes().hasAttrSomewhere(Attribute::SwiftError)) |
| continue; |
| |
| getOrCreateVRegUseAt(R, MBB, SwiftErrorArg); |
| } |
| } |
| } |