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/Twine.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 = Constant::getNullValue(IntIdxTy);
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     if (Constant *OpC = dyn_cast<Constant>(Op)) {
50       if (OpC->isZeroValue())
51         continue;
52 
53       // Handle a struct index, which adds its field offset to the pointer.
54       if (StructType *STy = GTI.getStructTypeOrNull()) {
55         uint64_t OpValue = OpC->getUniqueInteger().getZExtValue();
56         Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
57 
58         if (Size)
59           Result = Builder->CreateAdd(Result, ConstantInt::get(IntIdxTy, Size),
60                                       GEP->getName()+".offs");
61         continue;
62       }
63 
64       // Splat the constant if needed.
65       if (IntIdxTy->isVectorTy() && !OpC->getType()->isVectorTy())
66         OpC = ConstantVector::getSplat(IntIdxTy->getVectorNumElements(), OpC);
67 
68       Constant *Scale = ConstantInt::get(IntIdxTy, Size);
69       Constant *OC = ConstantExpr::getIntegerCast(OpC, IntIdxTy, true /*SExt*/);
70       Scale =
71           ConstantExpr::getMul(OC, Scale, false /*NUW*/, isInBounds /*NSW*/);
72       // Emit an add instruction.
73       Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
74       continue;
75     }
76 
77     // Splat the index if needed.
78     if (IntIdxTy->isVectorTy() && !Op->getType()->isVectorTy())
79       Op = Builder->CreateVectorSplat(IntIdxTy->getVectorNumElements(), Op);
80 
81     // Convert to correct type.
82     if (Op->getType() != IntIdxTy)
83       Op = Builder->CreateIntCast(Op, IntIdxTy, true, Op->getName()+".c");
84     if (Size != 1) {
85       // We'll let instcombine(mul) convert this to a shl if possible.
86       Op = Builder->CreateMul(Op, ConstantInt::get(IntIdxTy, Size),
87                               GEP->getName() + ".idx", false /*NUW*/,
88                               isInBounds /*NSW*/);
89     }
90 
91     // Emit an add instruction.
92     Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
93   }
94   return Result;
95 }
96 
97 }
98 
99 #endif // LLVM_TRANSFORMS_UTILS_LOCAL_H
100