llvm/lib/Analysis/TypeMetadataUtils.cpp

   1 //===- TypeMetadataUtils.cpp - Utilities related to type metadata ---------===//
   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 // This file contains functions that make it easier to manipulate type metadata
  10 // for devirtualization.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/TypeMetadataUtils.h"
  15 #include "llvm/IR/Constants.h"
  16 #include "llvm/IR/Dominators.h"
  17 #include "llvm/IR/Instructions.h"
  18 #include "llvm/IR/IntrinsicInst.h"
  19 #include "llvm/IR/Module.h"
  20
  21 using namespace llvm;
  22
  23 // Search for virtual calls that call FPtr and add them to DevirtCalls.
  24 static void
  25 findCallsAtConstantOffset(SmallVectorImpl<DevirtCallSite> &DevirtCalls,
  26                           bool *HasNonCallUses, Value *FPtr, uint64_t Offset,
  27                           const CallInst *CI, DominatorTree &DT) {
  28   for (const Use &U : FPtr->uses()) {
  29     Instruction *User = cast<Instruction>(U.getUser());
  30     // Ignore this instruction if it is not dominated by the type intrinsic
  31     // being analyzed. Otherwise we may transform a call sharing the same
  32     // vtable pointer incorrectly. Specifically, this situation can arise
  33     // after indirect call promotion and inlining, where we may have uses
  34     // of the vtable pointer guarded by a function pointer check, and a fallback
  35     // indirect call.
  36     if (!DT.dominates(CI, User))
  37       continue;
  38     if (isa<BitCastInst>(User)) {
  39       findCallsAtConstantOffset(DevirtCalls, HasNonCallUses, User, Offset, CI,
  40                                 DT);
  41     } else if (auto *CI = dyn_cast<CallInst>(User)) {
  42       DevirtCalls.push_back({Offset, *CI});
  43     } else if (auto *II = dyn_cast<InvokeInst>(User)) {
  44       DevirtCalls.push_back({Offset, *II});
  45     } else if (HasNonCallUses) {
  46       *HasNonCallUses = true;
  47     }
  48   }
  49 }
  50
  51 // Search for virtual calls that load from VPtr and add them to DevirtCalls.
  52 static void findLoadCallsAtConstantOffset(
  53     const Module *M, SmallVectorImpl<DevirtCallSite> &DevirtCalls, Value *VPtr,
  54     int64_t Offset, const CallInst *CI, DominatorTree &DT) {
  55   for (const Use &U : VPtr->uses()) {
  56     Value *User = U.getUser();
  57     if (isa<BitCastInst>(User)) {
  58       findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset, CI, DT);
  59     } else if (isa<LoadInst>(User)) {
  60       findCallsAtConstantOffset(DevirtCalls, nullptr, User, Offset, CI, DT);
  61     } else if (auto GEP = dyn_cast<GetElementPtrInst>(User)) {
  62       // Take into account the GEP offset.
  63       if (VPtr == GEP->getPointerOperand() && GEP->hasAllConstantIndices()) {
  64         SmallVector<Value *, 8> Indices(drop_begin(GEP->operands()));
  65         int64_t GEPOffset = M->getDataLayout().getIndexedOffsetInType(
  66             GEP->getSourceElementType(), Indices);
  67         findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset + GEPOffset,
  68                                       CI, DT);
  69       }
  70     }
  71   }
  72 }
  73
  74 void llvm::findDevirtualizableCallsForTypeTest(
  75     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
  76     SmallVectorImpl<CallInst *> &Assumes, const CallInst *CI,
  77     DominatorTree &DT) {
  78   assert(CI->getCalledFunction()->getIntrinsicID() == Intrinsic::type_test ||
  79          CI->getCalledFunction()->getIntrinsicID() ==
  80              Intrinsic::public_type_test);
  81
  82   const Module *M = CI->getParent()->getParent()->getParent();
  83
  84   // Find llvm.assume intrinsics for this llvm.type.test call.
  85   for (const Use &CIU : CI->uses())
  86     if (auto *Assume = dyn_cast<AssumeInst>(CIU.getUser()))
  87       Assumes.push_back(Assume);
  88
  89   // If we found any, search for virtual calls based on %p and add them to
  90   // DevirtCalls.
  91   if (!Assumes.empty())
  92     findLoadCallsAtConstantOffset(
  93         M, DevirtCalls, CI->getArgOperand(0)->stripPointerCasts(), 0, CI, DT);
  94 }
  95
  96 void llvm::findDevirtualizableCallsForTypeCheckedLoad(
  97     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
  98     SmallVectorImpl<Instruction *> &LoadedPtrs,
  99     SmallVectorImpl<Instruction *> &Preds, bool &HasNonCallUses,
 100     const CallInst *CI, DominatorTree &DT) {
 101   assert(CI->getCalledFunction()->getIntrinsicID() ==
 102              Intrinsic::type_checked_load ||
 103          CI->getCalledFunction()->getIntrinsicID() ==
 104              Intrinsic::type_checked_load_relative);
 105
 106   auto *Offset = dyn_cast<ConstantInt>(CI->getArgOperand(1));
 107   if (!Offset) {
 108     HasNonCallUses = true;
 109     return;
 110   }
 111
 112   for (const Use &U : CI->uses()) {
 113     auto CIU = U.getUser();
 114     if (auto EVI = dyn_cast<ExtractValueInst>(CIU)) {
 115       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 0) {
 116         LoadedPtrs.push_back(EVI);
 117         continue;
 118       }
 119       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 1) {
 120         Preds.push_back(EVI);
 121         continue;
 122       }
 123     }
 124     HasNonCallUses = true;
 125   }
 126
 127   for (Value *LoadedPtr : LoadedPtrs)
 128     findCallsAtConstantOffset(DevirtCalls, &HasNonCallUses, LoadedPtr,
 129                               Offset->getZExtValue(), CI, DT);
 130 }
 131
 132 Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M,
 133                                    Constant *TopLevelGlobal) {
 134   if (I->getType()->isPointerTy()) {
 135     if (Offset == 0)
 136       return I;
 137     return nullptr;
 138   }
 139
 140   const DataLayout &DL = M.getDataLayout();
 141
 142   if (auto *C = dyn_cast<ConstantStruct>(I)) {
 143     const StructLayout *SL = DL.getStructLayout(C->getType());
 144     if (Offset >= SL->getSizeInBytes())
 145       return nullptr;
 146
 147     unsigned Op = SL->getElementContainingOffset(Offset);
 148     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
 149                               Offset - SL->getElementOffset(Op), M,
 150                               TopLevelGlobal);
 151   }
 152   if (auto *C = dyn_cast<ConstantArray>(I)) {
 153     ArrayType *VTableTy = C->getType();
 154     uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
 155
 156     unsigned Op = Offset / ElemSize;
 157     if (Op >= C->getNumOperands())
 158       return nullptr;
 159
 160     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
 161                               Offset % ElemSize, M, TopLevelGlobal);
 162   }
 163
 164   // (Swift-specific) relative-pointer support starts here.
 165   if (auto *CI = dyn_cast<ConstantInt>(I)) {
 166     if (Offset == 0 && CI->isZero()) {
 167       return I;
 168     }
 169   }
 170   if (auto *C = dyn_cast<ConstantExpr>(I)) {
 171     switch (C->getOpcode()) {
 172     case Instruction::Trunc:
 173     case Instruction::PtrToInt:
 174       return getPointerAtOffset(cast<Constant>(C->getOperand(0)), Offset, M,
 175                                 TopLevelGlobal);
 176     case Instruction::Sub: {
 177       auto *Operand0 = cast<Constant>(C->getOperand(0));
 178       auto *Operand1 = cast<Constant>(C->getOperand(1));
 179
 180       auto StripGEP = [](Constant *C) {
 181         auto *CE = dyn_cast<ConstantExpr>(C);
 182         if (!CE)
 183           return C;
 184         if (CE->getOpcode() != Instruction::GetElementPtr)
 185           return C;
 186         return CE->getOperand(0);
 187       };
 188       auto *Operand1TargetGlobal = StripGEP(getPointerAtOffset(Operand1, 0, M));
 189
 190       // Check that in the "sub (@a, @b)" expression, @b points back to the top
 191       // level global (or a GEP thereof) that we're processing. Otherwise bail.
 192       if (Operand1TargetGlobal != TopLevelGlobal)
 193         return nullptr;
 194
 195       return getPointerAtOffset(Operand0, Offset, M, TopLevelGlobal);
 196     }
 197     default:
 198       return nullptr;
 199     }
 200   }
 201   return nullptr;
 202 }
 203
 204 void llvm::replaceRelativePointerUsersWithZero(Function *F) {
 205   for (auto *U : F->users()) {
 206     auto *PtrExpr = dyn_cast<ConstantExpr>(U);
 207     if (!PtrExpr || PtrExpr->getOpcode() != Instruction::PtrToInt)
 208       continue;
 209
 210     for (auto *PtrToIntUser : PtrExpr->users()) {
 211       auto *SubExpr = dyn_cast<ConstantExpr>(PtrToIntUser);
 212       if (!SubExpr || SubExpr->getOpcode() != Instruction::Sub)
 213         continue;
 214
 215       SubExpr->replaceNonMetadataUsesWith(
 216           ConstantInt::get(SubExpr->getType(), 0));
 217     }
 218   }
 219 }