r309058 - [CodeGen] Correctly model std::byte's aliasing properties

[David Majnemer via cfe-commits]

Should this go into 5.0 ?

On Tue, Jul 25, 2017 at 4:33 PM, David Majnemer via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: majnemer
> Date: Tue Jul 25 16:33:58 2017
> New Revision: 309058
>
> URL: http://llvm.org/viewvc/llvm-project?rev=309058&view=rev
> Log:
> [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
>
> Added:
>     cfe/trunk/test/CodeGenCXX/std-byte.cpp
> Modified:
>     cfe/trunk/include/clang/AST/Type.h
>     cfe/trunk/lib/AST/Type.cpp
>     cfe/trunk/lib/CodeGen/CodeGenTBAA.cpp
>
> Modified: cfe/trunk/include/clang/AST/Type.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/
> clang/AST/Type.h?rev=309058&r1=309057&r2=309058&view=diff
> ============================================================
> ==================
> --- cfe/trunk/include/clang/AST/Type.h (original)
> +++ cfe/trunk/include/clang/AST/Type.h Tue Jul 25 16:33:58 2017
> @@ -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) \
>
> Modified: cfe/trunk/lib/AST/Type.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/
> Type.cpp?rev=309058&r1=309057&r2=309058&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/AST/Type.cpp (original)
> +++ cfe/trunk/lib/AST/Type.cpp Tue Jul 25 16:33:58 2017
> @@ -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()) {
>
> Modified: cfe/trunk/lib/CodeGen/CodeGenTBAA.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/
> CodeGenTBAA.cpp?rev=309058&r1=309057&r2=309058&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/CodeGen/CodeGenTBAA.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CodeGenTBAA.cpp Tue Jul 25 16:33:58 2017
> @@ -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.
>
> Added: cfe/trunk/test/CodeGenCXX/std-byte.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> CodeGenCXX/std-byte.cpp?rev=309058&view=auto
> ============================================================
> ==================
> --- cfe/trunk/test/CodeGenCXX/std-byte.cpp (added)
> +++ cfe/trunk/test/CodeGenCXX/std-byte.cpp Tue Jul 25 16:33:58 2017
> @@ -0,0 +1,41 @@
> +// 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]]
>
>
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