[PATCH] D35824: [Sema] Implicitly apply the may_alias attribute to std::byte

[David Majnemer via Phabricator via cfe-commits]

majnemer updated this revision to Diff 108166.
majnemer added a comment.

- Address review comments


https://reviews.llvm.org/D35824

Files:
  include/clang/AST/Type.h
  lib/AST/Type.cpp
  lib/CodeGen/CodeGenTBAA.cpp
  test/CodeGenCXX/std-byte.cpp


Index: test/CodeGenCXX/std-byte.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/std-byte.cpp
@@ -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]]
Index: lib/CodeGen/CodeGenTBAA.cpp
===================================================================
--- lib/CodeGen/CodeGenTBAA.cpp
+++ lib/CodeGen/CodeGenTBAA.cpp
@@ -85,6 +85,12 @@
     return TypeHasMayAlias(TTy->desugar());
   }
 
+  // C++1z [intro.object]p3: If a complete object is created in storage
+  // associated with another object e of type [...] "array of N std::byte", that
+  // array provides storage for the created object [...].
+  if (QTy->isStdByteType())
+    return true;
+
   return false;
 }
 
Index: lib/AST/Type.cpp
===================================================================
--- lib/AST/Type.cpp
+++ lib/AST/Type.cpp
@@ -2313,6 +2313,15 @@
   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()) {
Index: include/clang/AST/Type.h
===================================================================
--- include/clang/AST/Type.h
+++ include/clang/AST/Type.h
@@ -1752,6 +1752,7 @@
   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) \


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