1 //===- Local.cpp - Functions to perform local transformations -------------===//
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 #include "llvm/Analysis/Utils/Local.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/IR/DataLayout.h"
17 #include "llvm/IR/GetElementPtrTypeIterator.h"
18 #include "llvm/IR/IRBuilder.h"
19 
20 using namespace llvm;
21 
22 Value *llvm::emitGEPOffset(IRBuilderBase *Builder, const DataLayout &DL,
23                            User *GEP, bool NoAssumptions) {
24   GEPOperator *GEPOp = cast<GEPOperator>(GEP);
25   Type *IntIdxTy = DL.getIndexType(GEP->getType());
26   Value *Result = nullptr;
27 
28   // If the GEP is inbounds, we know that none of the addressing operations will
29   // overflow in a signed sense.
30   bool isInBounds = GEPOp->isInBounds() && !NoAssumptions;
31 
32   // Build a mask for high order bits.
33   unsigned IntPtrWidth = IntIdxTy->getScalarType()->getIntegerBitWidth();
34   uint64_t PtrSizeMask =
35       std::numeric_limits<uint64_t>::max() >> (64 - IntPtrWidth);
36 
37   gep_type_iterator GTI = gep_type_begin(GEP);
38   for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
39        ++i, ++GTI) {
40     Value *Op = *i;
41     uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
42     Value *Offset;
43     if (Constant *OpC = dyn_cast<Constant>(Op)) {
44       if (OpC->isZeroValue())
45         continue;
46 
47       // Handle a struct index, which adds its field offset to the pointer.
48       if (StructType *STy = GTI.getStructTypeOrNull()) {
49         uint64_t OpValue = OpC->getUniqueInteger().getZExtValue();
50         Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
51         if (!Size)
52           continue;
53 
54         Offset = ConstantInt::get(IntIdxTy, Size);
55       } else {
56         // Splat the constant if needed.
57         if (IntIdxTy->isVectorTy() && !OpC->getType()->isVectorTy())
58           OpC = ConstantVector::getSplat(
59               cast<VectorType>(IntIdxTy)->getElementCount(), OpC);
60 
61         Constant *Scale = ConstantInt::get(IntIdxTy, Size);
62         Constant *OC =
63             ConstantExpr::getIntegerCast(OpC, IntIdxTy, true /*SExt*/);
64         Offset =
65             ConstantExpr::getMul(OC, Scale, false /*NUW*/, isInBounds /*NSW*/);
66       }
67     } else {
68       // Splat the index if needed.
69       if (IntIdxTy->isVectorTy() && !Op->getType()->isVectorTy())
70         Op = Builder->CreateVectorSplat(
71             cast<FixedVectorType>(IntIdxTy)->getNumElements(), Op);
72 
73       // Convert to correct type.
74       if (Op->getType() != IntIdxTy)
75         Op = Builder->CreateIntCast(Op, IntIdxTy, true, Op->getName() + ".c");
76       if (Size != 1) {
77         // We'll let instcombine(mul) convert this to a shl if possible.
78         Op = Builder->CreateMul(Op, ConstantInt::get(IntIdxTy, Size),
79                                 GEP->getName() + ".idx", false /*NUW*/,
80                                 isInBounds /*NSW*/);
81       }
82       Offset = Op;
83     }
84 
85     if (Result)
86       Result = Builder->CreateAdd(Result, Offset, GEP->getName() + ".offs",
87                                   false /*NUW*/, isInBounds /*NSW*/);
88     else
89       Result = Offset;
90   }
91   return Result ? Result : Constant::getNullValue(IntIdxTy);
92 }
93