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
20using namespace llvm;
21
22Value *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  auto AddOffset = [&](Value *Offset) {
32    if (Result)
33      Result = Builder->CreateAdd(Result, Offset, GEP->getName() + ".offs",
34                                  false /*NUW*/, isInBounds /*NSW*/);
35    else
36      Result = Offset;
37  };
38
39  gep_type_iterator GTI = gep_type_begin(GEP);
40  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
41       ++i, ++GTI) {
42    Value *Op = *i;
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        uint64_t Size = DL.getStructLayout(STy)->getElementOffset(OpValue);
51        if (!Size)
52          continue;
53
54        AddOffset(ConstantInt::get(IntIdxTy, Size));
55        continue;
56      }
57    }
58
59    // Splat the index if needed.
60    if (IntIdxTy->isVectorTy() && !Op->getType()->isVectorTy())
61      Op = Builder->CreateVectorSplat(
62          cast<VectorType>(IntIdxTy)->getElementCount(), Op);
63
64    // Convert to correct type.
65    if (Op->getType() != IntIdxTy)
66      Op = Builder->CreateIntCast(Op, IntIdxTy, true, Op->getName() + ".c");
67    TypeSize TSize = GTI.getSequentialElementStride(DL);
68    if (TSize != TypeSize::getFixed(1)) {
69      Value *Scale = Builder->CreateTypeSize(IntIdxTy->getScalarType(), TSize);
70      if (IntIdxTy->isVectorTy())
71        Scale = Builder->CreateVectorSplat(
72            cast<VectorType>(IntIdxTy)->getElementCount(), Scale);
73      // We'll let instcombine(mul) convert this to a shl if possible.
74      Op = Builder->CreateMul(Op, Scale, GEP->getName() + ".idx", false /*NUW*/,
75                              isInBounds /*NSW*/);
76    }
77    AddOffset(Op);
78  }
79  return Result ? Result : Constant::getNullValue(IntIdxTy);
80}
81