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
emitGEPOffset(IRBuilderBase * Builder,const DataLayout & DL,User * GEP,bool NoAssumptions)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