include/llvm/Analysis/Utils/Local.h

   1 //===- Local.h - Functions to perform local transformations -----*- C++ -*-===//
   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 family of functions perform various local transformations to the
  10 // program.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_ANALYSIS_UTILS_LOCAL_H
  15 #define LLVM_ANALYSIS_UTILS_LOCAL_H
  16
  17 #include "llvm/IR/DataLayout.h"
  18 #include "llvm/IR/GetElementPtrTypeIterator.h"
  19
  20 namespace llvm {
  21
  22 /// Given a getelementptr instruction/constantexpr, emit the code necessary to
  23 /// compute the offset from the base pointer (without adding in the base
  24 /// pointer). Return the result as a signed integer of intptr size.
  25 /// When NoAssumptions is true, no assumptions about index computation not
  26 /// overflowing is made.
  27 template <typename IRBuilderTy>
  28 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &DL, User *GEP,
  29                      bool NoAssumptions = false) {
  30   GEPOperator *GEPOp = cast<GEPOperator>(GEP);
  31   Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
  32   Value *Result = Constant::getNullValue(IntPtrTy);
  33
  34   // If the GEP is inbounds, we know that none of the addressing operations will
  35   // overflow in an unsigned sense.
  36   bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
  37
  38   // Build a mask for high order bits.
  39   unsigned IntPtrWidth = IntPtrTy->getScalarType()->getIntegerBitWidth();
  40   uint64_t PtrSizeMask =
  41       std::numeric_limits<uint64_t>::max() >> (64 - IntPtrWidth);
  42
  43   gep_type_iterator GTI = gep_type_begin(GEP);
  44   for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
  45        ++i, ++GTI) {
  46     Value *Op = *i;
  47     uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
  48     if (Constant *OpC = dyn_cast<Constant>(Op)) {
  49       if (OpC->isZeroValue())
  50         continue;
  51
  52       // Handle a struct index, which adds its field offset to the pointer.
  53       if (StructType *STy = GTI.getStructTypeOrNull()) {
  54         uint64_t OpValue = OpC->getUniqueInteger().getZExtValue();
  55         Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
  56
  57         if (Size)
  58           Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
  59                                       GEP->getName()+".offs");
  60         continue;
  61       }
  62
  63       // Splat the constant if needed.
  64       if (IntPtrTy->isVectorTy() && !OpC->getType()->isVectorTy())
  65         OpC = ConstantVector::getSplat(IntPtrTy->getVectorNumElements(), OpC);
  66
  67       Constant *Scale = ConstantInt::get(IntPtrTy, Size);
  68       Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
  69       Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/);
  70       // Emit an add instruction.
  71       Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
  72       continue;
  73     }
  74
  75     // Splat the index if needed.
  76     if (IntPtrTy->isVectorTy() && !Op->getType()->isVectorTy())
  77       Op = Builder->CreateVectorSplat(IntPtrTy->getVectorNumElements(), Op);
  78
  79     // Convert to correct type.
  80     if (Op->getType() != IntPtrTy)
  81       Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
  82     if (Size != 1) {
  83       // We'll let instcombine(mul) convert this to a shl if possible.
  84       Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size),
  85                               GEP->getName()+".idx", isInBounds /*NUW*/);
  86     }
  87
  88     // Emit an add instruction.
  89     Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
  90   }
  91   return Result;
  92 }
  93
  94 }
  95
  96 #endif // LLVM_TRANSFORMS_UTILS_LOCAL_H