llvm/lib/Target/BPF/BPFASpaceCastSimplifyPass.cpp

   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>(I);
  28     if (!OuterCast)
  29       return std::nullopt;
  30     auto *GEP = dyn_cast<GetElementPtrInst>(OuterCast->getPointerOperand());
  31     if (!GEP)
  32       return std::nullopt;
  33     auto *InnerCast = dyn_cast<AddrSpaceCastInst>(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};
  41   }
  42
  43   static PointerType *changeAddressSpace(PointerType *Ty, unsigned AS) {
  44     return Ty->get(Ty->getContext(), 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>(OuterCast->getPointerOperand());
  53     auto *InnerCast = cast<AddrSpaceCastInst>(GEP->getPointerOperand());
  54     unsigned AS = OuterCast->getDestAddressSpace();
  55     auto *NewGEP = cast<GetElementPtrInst>(GEP->clone());
  56     NewGEP->setName(GEP->getName());
  57     NewGEP->insertAfter(OuterCast);
  58     NewGEP->setOperand(0, InnerCast->getPointerOperand());
  59     auto *GEPTy = cast<PointerType>(GEP->getType());
  60     NewGEP->mutateType(changeAddressSpace(GEPTy, AS));
  61     OuterCast->replaceAllUsesWith(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))
  80         WorkList.push_back(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(U))
  88           WorkList.push_back(It.value());
  89     }
  90   }
  91   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
  92 }