Commit 819eb09f authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r309058: 

------------------------------------------------------------------------
r309058 | majnemer | 2017-07-25 16:33:58 -0700 (Tue, 25 Jul 2017) | 9 lines

[CodeGen] Correctly model std::byte's aliasing properties

std::byte, when defined as an enum, needs to be given special treatment
with regards to its aliasing properties. An array of std::byte is
allowed to be used as storage for other types.

This fixes PR33916.

Differential Revision: https://reviews.llvm.org/D35824
------------------------------------------------------------------------

llvm-svn: 309135
parent dfe8875c

clang/include/clang/AST/Type.h

+1 −0
Original line number Diff line number Diff line
@@ -1752,6 +1752,7 @@ public: 
  bool isTemplateTypeParmType() const;          // C++ template type parameter

  bool isNullPtrType() const;                   // C++11 std::nullptr_t

  bool isAlignValT() const;                     // C++17 std::align_val_t

  bool isStdByteType() const;                   // C++17 std::byte

  bool isAtomicType() const;                    // C11 _Atomic()



#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \

clang/lib/AST/Type.cpp

+9 −0
Original line number Diff line number Diff line
@@ -2313,6 +2313,15 @@ bool Type::isAlignValT() const { 
  return false;

}



bool Type::isStdByteType() const {

  if (auto *ET = getAs<EnumType>()) {

    auto *II = ET->getDecl()->getIdentifier();

    if (II && II->isStr("byte") && ET->getDecl()->isInStdNamespace())

      return true;

  }

  return false;

}



bool Type::isPromotableIntegerType() const {

  if (const BuiltinType *BT = getAs<BuiltinType>())

    switch (BT->getKind()) {

clang/lib/CodeGen/CodeGenTBAA.cpp

+6 −0
Original line number Diff line number Diff line
@@ -139,6 +139,12 @@ CodeGenTBAA::getTBAAInfo(QualType QTy) { 
    }

  }



  // C++1z [basic.lval]p10: "If a program attempts to access the stored value of

  // an object through a glvalue of other than one of the following types the

  // behavior is undefined: [...] a char, unsigned char, or std::byte type."

  if (Ty->isStdByteType())

    return MetadataCache[Ty] = getChar();



  // Handle pointers.

  // TODO: Implement C++'s type "similarity" and consider dis-"similar"

  // pointers distinct.

clang/test/CodeGenCXX/std-byte.cpp

0 → 100644
+41 −0
Original line number Diff line number Diff line 
// RUN: %clang_cc1 -std=c++1z -Werror -triple i386-unknown-unknown -emit-llvm -O1 -disable-llvm-passes -o - %s | FileCheck %s



// std::byte should be considered equivalent to char for aliasing.



namespace std {

enum byte : unsigned char {};

}



// CHECK-LABEL: define void @test0(

extern "C" void test0(std::byte *sb, int *i) {

  // CHECK: store i8 0, i8* %{{.*}} !tbaa [[TAG_CHAR:!.*]]

  *sb = std::byte{0};



  // CHECK: store i32 1, i32* %{{.*}} !tbaa [[TAG_INT:!.*]]

  *i = 1;

}



enum byte : unsigned char {};

namespace my {

enum byte : unsigned char {};

namespace std {

enum byte : unsigned char {};

} // namespace std

} // namespace my



// Make sure we don't get confused with other enums named 'byte'.



// CHECK-LABEL: define void @test1(

extern "C" void test1(::byte *b, ::my::byte *mb, ::my::std::byte *msb) {

  *b = ::byte{0};

  *mb = ::my::byte{0};

  *msb = ::my::std::byte{0};

  // CHECK-NOT: store i8 0, i8* %{{.*}} !tbaa [[TAG_CHAR]]

}



// CHECK:  !"any pointer", [[TYPE_CHAR:!.*]],

// CHECK: [[TYPE_CHAR]] = !{!"omnipotent char", [[TAG_CXX_TBAA:!.*]],

// CHECK: [[TAG_CXX_TBAA]] = !{!"Simple C++ TBAA"}

// CHECK: [[TAG_CHAR]] = !{[[TYPE_CHAR:!.*]], [[TYPE_CHAR]], i64 0}

// CHECK: [[TAG_INT]] = !{[[TYPE_INT:!.*]], [[TYPE_INT]], i64 0}

// CHECK: [[TYPE_INT]] = !{!"int", [[TYPE_CHAR]]