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/ADT/StringRef.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/GetElementPtrTypeIterator.h"
20 
21 namespace llvm {
22 
23 /// Given a getelementptr instruction/constantexpr, emit the code necessary to
24 /// compute the offset from the base pointer (without adding in the base
25 /// pointer). Return the result as a signed integer of intptr size.
26 /// When NoAssumptions is true, no assumptions about index computation not
27 /// overflowing is made.
28 template <typename IRBuilderTy>
29 Value *EmitGEPOffset(IRBuilderTy *Builder, const DataLayout &DL, User *GEP,
30                      bool NoAssumptions = false) {
31   GEPOperator *GEPOp = cast<GEPOperator>(GEP);
32   Type *IntIdxTy = DL.getIndexType(GEP->getType());
33   Value *Result = nullptr;
34 
35   // If the GEP is inbounds, we know that none of the addressing operations will
36   // overflow in a signed sense.
37   bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
38 
39   // Build a mask for high order bits.
40   unsigned IntPtrWidth = IntIdxTy->getScalarType()->getIntegerBitWidth();
41   uint64_t PtrSizeMask =
42       std::numeric_limits<uint64_t>::max() >> (64 - IntPtrWidth);
43 
44   gep_type_iterator GTI = gep_type_begin(GEP);
45   for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
46        ++i, ++GTI) {
47     Value *Op = *i;
48     uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
49     Value *Offset;
50     if (Constant *OpC = dyn_cast<Constant>(Op)) {
51       if (OpC->isZeroValue())
52         continue;
53 
54       // Handle a struct index, which adds its field offset to the pointer.
55       if (StructType *STy = GTI.getStructTypeOrNull()) {
56         uint64_t OpValue = OpC->getUniqueInteger().getZExtValue();
57         Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
58         if (!Size)
59           continue;
60 
61         Offset = ConstantInt::get(IntIdxTy, Size);
62       } else {
63         // Splat the constant if needed.
64         if (IntIdxTy->isVectorTy() && !OpC->getType()->isVectorTy())
65           OpC = ConstantVector::getSplat(
66               cast<VectorType>(IntIdxTy)->getElementCount(), OpC);
67 
68         Constant *Scale = ConstantInt::get(IntIdxTy, Size);
69         Constant *OC =
70             ConstantExpr::getIntegerCast(OpC, IntIdxTy, true /*SExt*/);
71         Offset =
72             ConstantExpr::getMul(OC, Scale, false /*NUW*/, isInBounds /*NSW*/);
73       }
74     } else {
75       // Splat the index if needed.
76       if (IntIdxTy->isVectorTy() && !Op->getType()->isVectorTy())
77         Op = Builder->CreateVectorSplat(
78             cast<FixedVectorType>(IntIdxTy)->getNumElements(), Op);
79 
80       // Convert to correct type.
81       if (Op->getType() != IntIdxTy)
82         Op = Builder->CreateIntCast(Op, IntIdxTy, true, Op->getName().str()+".c");
83       if (Size != 1) {
84         // We'll let instcombine(mul) convert this to a shl if possible.
85         Op = Builder->CreateMul(Op, ConstantInt::get(IntIdxTy, Size),
86                                 GEP->getName().str() + ".idx", false /*NUW*/,
87                                 isInBounds /*NSW*/);
88       }
89       Offset = Op;
90     }
91 
92     if (Result)
93       Result = Builder->CreateAdd(Result, Offset, GEP->getName().str()+".offs",
94                                   false /*NUW*/, isInBounds /*NSW*/);
95     else
96       Result = Offset;
97   }
98   return Result ? Result : Constant::getNullValue(IntIdxTy);
99 }
100 
101 }
102 
103 #endif // LLVM_ANALYSIS_UTILS_LOCAL_H
104