| 1 | //===-- BPFASpaceCastSimplifyPass.cpp - BPF addrspacecast simplications --===// |
|---|---|
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | |
| 9 | #include "BPF.h" |
| 10 | #include <optional> |
| 11 | |
| 12 | #define DEBUG_TYPE "bpf-aspace-simplify" |
| 13 | |
| 14 | using namespace llvm; |
| 15 | |
| 16 | namespace { |
| 17 | |
| 18 | struct CastGEPCast { |
| 19 | AddrSpaceCastInst *OuterCast; |
| 20 | |
| 21 | // Match chain of instructions: |
| 22 | // %inner = addrspacecast N->M |
| 23 | // %gep = getelementptr %inner, ... |
| 24 | // %outer = addrspacecast M->N %gep |
| 25 | // Where I is %outer. |
| 26 | static std::optional<CastGEPCast> match(Value *I) { |
| 27 | auto *OuterCast = dyn_cast<AddrSpaceCastInst>(Val: I); |
| 28 | if (!OuterCast) |
| 29 | return std::nullopt; |
| 30 | auto *GEP = dyn_cast<GetElementPtrInst>(Val: OuterCast->getPointerOperand()); |
| 31 | if (!GEP) |
| 32 | return std::nullopt; |
| 33 | auto *InnerCast = dyn_cast<AddrSpaceCastInst>(Val: GEP->getPointerOperand()); |
| 34 | if (!InnerCast) |
| 35 | return std::nullopt; |
| 36 | if (InnerCast->getSrcAddressSpace() != OuterCast->getDestAddressSpace()) |
| 37 | return std::nullopt; |
| 38 | if (InnerCast->getDestAddressSpace() != OuterCast->getSrcAddressSpace()) |
| 39 | return std::nullopt; |
| 40 | return CastGEPCast{.OuterCast: OuterCast}; |
| 41 | } |
| 42 | |
| 43 | static PointerType *changeAddressSpace(PointerType *Ty, unsigned AS) { |
| 44 | return Ty->get(C&: Ty->getContext(), AddressSpace: AS); |
| 45 | } |
| 46 | |
| 47 | // Assuming match(this->OuterCast) is true, convert: |
| 48 | // (addrspacecast M->N (getelementptr (addrspacecast N->M ptr) ...)) |
| 49 | // To: |
| 50 | // (getelementptr ptr ...) |
| 51 | GetElementPtrInst *rewrite() { |
| 52 | auto *GEP = cast<GetElementPtrInst>(Val: OuterCast->getPointerOperand()); |
| 53 | auto *InnerCast = cast<AddrSpaceCastInst>(Val: GEP->getPointerOperand()); |
| 54 | unsigned AS = OuterCast->getDestAddressSpace(); |
| 55 | auto *NewGEP = cast<GetElementPtrInst>(Val: GEP->clone()); |
| 56 | NewGEP->setName(GEP->getName()); |
| 57 | NewGEP->insertAfter(InsertPos: OuterCast); |
| 58 | NewGEP->setOperand(i_nocapture: 0, Val_nocapture: InnerCast->getPointerOperand()); |
| 59 | auto *GEPTy = cast<PointerType>(Val: GEP->getType()); |
| 60 | NewGEP->mutateType(Ty: changeAddressSpace(Ty: GEPTy, AS)); |
| 61 | OuterCast->replaceAllUsesWith(V: NewGEP); |
| 62 | OuterCast->eraseFromParent(); |
| 63 | if (GEP->use_empty()) |
| 64 | GEP->eraseFromParent(); |
| 65 | if (InnerCast->use_empty()) |
| 66 | InnerCast->eraseFromParent(); |
| 67 | return NewGEP; |
| 68 | } |
| 69 | }; |
| 70 | |
| 71 | } // anonymous namespace |
| 72 | |
| 73 | PreservedAnalyses BPFASpaceCastSimplifyPass::run(Function &F, |
| 74 | FunctionAnalysisManager &AM) { |
| 75 | SmallVector<CastGEPCast, 16> WorkList; |
| 76 | bool Changed = false; |
| 77 | for (BasicBlock &BB : F) { |
| 78 | for (Instruction &I : BB) |
| 79 | if (auto It = CastGEPCast::match(I: &I)) |
| 80 | WorkList.push_back(Elt: It.value()); |
| 81 | Changed |= !WorkList.empty(); |
| 82 | |
| 83 | while (!WorkList.empty()) { |
| 84 | CastGEPCast InsnChain = WorkList.pop_back_val(); |
| 85 | GetElementPtrInst *NewGEP = InsnChain.rewrite(); |
| 86 | for (User *U : NewGEP->users()) |
| 87 | if (auto It = CastGEPCast::match(I: U)) |
| 88 | WorkList.push_back(Elt: It.value()); |
| 89 | } |
| 90 | } |
| 91 | return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all(); |
| 92 | } |
| 93 |