clang  10.0.0svn
PatternInit.cpp
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1 //===--- PatternInit.cpp - Pattern Initialization -------------------------===//
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 #include "PatternInit.h"
10 #include "CodeGenModule.h"
11 #include "llvm/IR/Constant.h"
12 #include "llvm/IR/Type.h"
13 
15  llvm::Type *Ty) {
16  // The following value is a guaranteed unmappable pointer value and has a
17  // repeated byte-pattern which makes it easier to synthesize. We use it for
18  // pointers as well as integers so that aggregates are likely to be
19  // initialized with this repeated value.
20  // For 32-bit platforms it's a bit trickier because, across systems, only the
21  // zero page can reasonably be expected to be unmapped. We use max 0xFFFFFFFF
22  // assuming that memory access will overlap into zero page.
23  const uint64_t IntValue =
25  ? 0xFFFFFFFFFFFFFFFFull
26  : 0xAAAAAAAAAAAAAAAAull;
27  // Floating-point values are initialized as NaNs because they propagate. Using
28  // a repeated byte pattern means that it will be easier to initialize
29  // all-floating-point aggregates and arrays with memset. Further, aggregates
30  // which mix integral and a few floats might also initialize with memset
31  // followed by a handful of stores for the floats. Using fairly unique NaNs
32  // also means they'll be easier to distinguish in a crash.
33  constexpr bool NegativeNaN = true;
34  constexpr uint64_t NaNPayload = 0xFFFFFFFFFFFFFFFFull;
35  if (Ty->isIntOrIntVectorTy()) {
36  unsigned BitWidth = cast<llvm::IntegerType>(
37  Ty->isVectorTy() ? Ty->getVectorElementType() : Ty)
38  ->getBitWidth();
39  if (BitWidth <= 64)
40  return llvm::ConstantInt::get(Ty, IntValue);
41  return llvm::ConstantInt::get(
42  Ty, llvm::APInt::getSplat(BitWidth, llvm::APInt(64, IntValue)));
43  }
44  if (Ty->isPtrOrPtrVectorTy()) {
45  auto *PtrTy = cast<llvm::PointerType>(
46  Ty->isVectorTy() ? Ty->getVectorElementType() : Ty);
47  unsigned PtrWidth = CGM.getContext().getTargetInfo().getPointerWidth(
48  PtrTy->getAddressSpace());
49  if (PtrWidth > 64)
50  llvm_unreachable("pattern initialization of unsupported pointer width");
51  llvm::Type *IntTy = llvm::IntegerType::get(CGM.getLLVMContext(), PtrWidth);
52  auto *Int = llvm::ConstantInt::get(IntTy, IntValue);
53  return llvm::ConstantExpr::getIntToPtr(Int, PtrTy);
54  }
55  if (Ty->isFPOrFPVectorTy()) {
56  unsigned BitWidth = llvm::APFloat::semanticsSizeInBits(
57  (Ty->isVectorTy() ? Ty->getVectorElementType() : Ty)
58  ->getFltSemantics());
59  llvm::APInt Payload(64, NaNPayload);
60  if (BitWidth >= 64)
61  Payload = llvm::APInt::getSplat(BitWidth, Payload);
62  return llvm::ConstantFP::getQNaN(Ty, NegativeNaN, &Payload);
63  }
64  if (Ty->isArrayTy()) {
65  // Note: this doesn't touch tail padding (at the end of an object, before
66  // the next array object). It is instead handled by replaceUndef.
67  auto *ArrTy = cast<llvm::ArrayType>(Ty);
69  ArrTy->getNumElements(),
70  initializationPatternFor(CGM, ArrTy->getElementType()));
71  return llvm::ConstantArray::get(ArrTy, Element);
72  }
73 
74  // Note: this doesn't touch struct padding. It will initialize as much union
75  // padding as is required for the largest type in the union. Padding is
76  // instead handled by replaceUndef. Stores to structs with volatile members
77  // don't have a volatile qualifier when initialized according to C++. This is
78  // fine because stack-based volatiles don't really have volatile semantics
79  // anyways, and the initialization shouldn't be observable.
80  auto *StructTy = cast<llvm::StructType>(Ty);
81  llvm::SmallVector<llvm::Constant *, 8> Struct(StructTy->getNumElements());
82  for (unsigned El = 0; El != Struct.size(); ++El)
83  Struct[El] = initializationPatternFor(CGM, StructTy->getElementType(El));
84  return llvm::ConstantStruct::get(StructTy, Struct);
85 }
llvm::Constant * initializationPatternFor(CodeGenModule &, llvm::Type *)
Definition: PatternInit.cpp:14
llvm::LLVMContext & getLLVMContext()
const TargetInfo & getTargetInfo() const
Definition: ASTContext.h:706
uint64_t getPointerWidth(unsigned AddrSpace) const
Return the width of pointers on this target, for the specified address space.
Definition: TargetInfo.h:360
ASTContext & getContext() const
llvm::APInt APInt
Definition: Integral.h:27
This class organizes the cross-function state that is used while generating LLVM code.
virtual uint64_t getMaxPointerWidth() const
Return the maximum width of pointers on this target.
Definition: TargetInfo.h:368