Local.h revision 360784 
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
21namespace 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.
28template <typename IRBuilderTy>
29Value *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