Commit e0e07a7e authored by Richard Smith's avatar Richard Smith
Browse files

Fix detection of __attribute__((may_alias)) to properly look through 

type sugar.

We previously missed the attribute in a lot of cases in C++, because
there's often other type sugar there (eg, ElaboratedType).
parent cdf5cfea

clang/lib/CodeGen/CodeGenTBAA.cpp

+9 −8
Original line number Diff line number Diff line
@@ -78,17 +78,18 @@ llvm::MDNode *CodeGenTBAA::getChar() { 


static bool TypeHasMayAlias(QualType QTy) {

  // Tagged types have declarations, and therefore may have attributes.

  if (const TagType *TTy = dyn_cast<TagType>(QTy))

    return TTy->getDecl()->hasAttr<MayAliasAttr>();

  if (auto *TD = QTy->getAsTagDecl())

    if (TD->hasAttr<MayAliasAttr>())

      return true;



  // Typedef types have declarations, and therefore may have attributes.

  if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) {

    if (TTy->getDecl()->hasAttr<MayAliasAttr>())

  // Also look for may_alias as a declaration attribute on a typedef.

  // FIXME: We should follow GCC and model may_alias as a type attribute

  // rather than as a declaration attribute.

  while (auto *TT = QTy->getAs<TypedefType>()) {

    if (TT->getDecl()->hasAttr<MayAliasAttr>())

      return true;

    // Also, their underlying types may have relevant attributes.

    return TypeHasMayAlias(TTy->desugar());

    QTy = TT->desugar();

  }



  return false;

}

clang/test/CodeGenCXX/may_alias.cpp

0 → 100644
+25 −0
Original line number Diff line number Diff line 
// RUN: %clang_cc1 %s -triple %itanium_abi_triple -emit-llvm -O2 -disable-llvm-passes -o - | FileCheck %s

// RUN: %clang_cc1 %s -triple %ms_abi_triple -emit-llvm -O2 -disable-llvm-passes -o - | FileCheck %s



enum class __attribute__((may_alias)) E {};



template<typename T> struct A {

  using B __attribute__((may_alias)) = enum {};

};



template<typename T> using Alias = typename A<T>::B;



// CHECK-LABEL: define {{.*}}foo

// CHECK: load i{{[0-9]*}}, {{.*}}, !tbaa ![[MAY_ALIAS:[^ ,]*]]

auto foo(E &r) { return r; }



// CHECK-LABEL: define {{.*}}goo

// CHECK: load i{{[0-9]*}}, {{.*}}, !tbaa ![[MAY_ALIAS]]

auto goo(A<int>::B &r) { return r; }



// CHECK-LABEL: define {{.*}}hoo

// CHECK: load i{{[0-9]*}}, {{.*}}, !tbaa ![[MAY_ALIAS]]

auto hoo(Alias<int> &r) { return r; }



// CHECK: ![[CHAR:.*]] = !{!"omnipotent char", !{{.*}}, i64 0}

// CHECK: ![[MAY_ALIAS]] = !{![[CHAR]], ![[CHAR]], i64 0}