Canonicalize declaration pointers when forming APValues.

References to different declarations of the same entity aren't different
values, so shouldn't have different representations.

Recommit of e6393ee with fixed handling
for weak declarations. We now look for attributes on the most recent
declaration when determining whether a declaration is weak. (Second
recommit with further fixes for mishandling of weak declarations. Our
behavior here is fundamentally unsound -- see PR47663 -- but this
approach attempts to not make things worse.)

Author: zygoloid

clang/include/clang/AST/APValue.h

@@ -174,6 +174,7 @@ class APValue {
       return !(LHS == RHS);
     }
     friend llvm::hash_code hash_value(const LValueBase &Base);
+    friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
     PtrTy Ptr;
@@ -201,8 +202,7 @@ class APValue {
 
   public:
     LValuePathEntry() : Value() {}
-    LValuePathEntry(BaseOrMemberType BaseOrMember)
-        : Value{reinterpret_cast<uintptr_t>(BaseOrMember.getOpaqueValue())} {}
+    LValuePathEntry(BaseOrMemberType BaseOrMember);
     static LValuePathEntry ArrayIndex(uint64_t Index) {
       LValuePathEntry Result;
       Result.Value = Index;

clang/lib/AST/APValue.cpp

@@ -38,7 +38,7 @@ static_assert(
     "Type is insufficiently aligned");
 
 APValue::LValueBase::LValueBase(const ValueDecl *P, unsigned I, unsigned V)
-    : Ptr(P), Local{I, V} {}
+    : Ptr(P ? cast<ValueDecl>(P->getCanonicalDecl()) : nullptr), Local{I, V} {}
 APValue::LValueBase::LValueBase(const Expr *P, unsigned I, unsigned V)
     : Ptr(P), Local{I, V} {}
 
@@ -82,13 +82,19 @@ bool operator==(const APValue::LValueBase &LHS,
                 const APValue::LValueBase &RHS) {
   if (LHS.Ptr != RHS.Ptr)
     return false;
-  if (LHS.is<TypeInfoLValue>())
+  if (LHS.is<TypeInfoLValue>() || LHS.is<DynamicAllocLValue>())
     return true;
   return LHS.Local.CallIndex == RHS.Local.CallIndex &&
          LHS.Local.Version == RHS.Local.Version;
 }
 }
 
+APValue::LValuePathEntry::LValuePathEntry(BaseOrMemberType BaseOrMember) {
+  if (const Decl *D = BaseOrMember.getPointer())
+    BaseOrMember.setPointer(D->getCanonicalDecl());
+  Value = reinterpret_cast<uintptr_t>(BaseOrMember.getOpaqueValue());
+}
+
 namespace {
   struct LVBase {
     APValue::LValueBase Base;
@@ -113,14 +119,16 @@ APValue::LValueBase::operator bool () const {
 
 clang::APValue::LValueBase
 llvm::DenseMapInfo<clang::APValue::LValueBase>::getEmptyKey() {
-  return clang::APValue::LValueBase(
-      DenseMapInfo<const ValueDecl*>::getEmptyKey());
+  clang::APValue::LValueBase B;
+  B.Ptr = DenseMapInfo<const ValueDecl*>::getEmptyKey();
+  return B;
 }
 
 clang::APValue::LValueBase
 llvm::DenseMapInfo<clang::APValue::LValueBase>::getTombstoneKey() {
-  return clang::APValue::LValueBase(
-      DenseMapInfo<const ValueDecl*>::getTombstoneKey());
+  clang::APValue::LValueBase B;
+  B.Ptr = DenseMapInfo<const ValueDecl*>::getTombstoneKey();
+  return B;
 }
 
 namespace clang {
@@ -773,8 +781,10 @@ void APValue::MakeMemberPointer(const ValueDecl *Member, bool IsDerivedMember,
   assert(isAbsent() && "Bad state change");
   MemberPointerData *MPD = new ((void*)(char*)Data.buffer) MemberPointerData;
   Kind = MemberPointer;
-  MPD->MemberAndIsDerivedMember.setPointer(Member);
+  MPD->MemberAndIsDerivedMember.setPointer(
+      Member ? cast<ValueDecl>(Member->getCanonicalDecl()) : nullptr);
   MPD->MemberAndIsDerivedMember.setInt(IsDerivedMember);
   MPD->resizePath(Path.size());
-  memcpy(MPD->getPath(), Path.data(), Path.size()*sizeof(const CXXRecordDecl*));
+  for (unsigned I = 0; I != Path.size(); ++I)
+    MPD->getPath()[I] = Path[I]->getCanonicalDecl();
 }

clang/lib/AST/Decl.cpp

@@ -4686,11 +4686,9 @@ char *Buffer = new (getASTContext(), 1) char[Name.size() + 1];
 void ValueDecl::anchor() {}
 
 bool ValueDecl::isWeak() const {
-  for (const auto *I : attrs())
-    if (isa<WeakAttr>(I) || isa<WeakRefAttr>(I))
-      return true;
-
-  return isWeakImported();
+  auto *MostRecent = getMostRecentDecl();
+  return MostRecent->hasAttr<WeakAttr>() ||
+         MostRecent->hasAttr<WeakRefAttr>() || isWeakImported();
 }
 
 void ImplicitParamDecl::anchor() {}

clang/lib/AST/DeclBase.cpp

@@ -720,7 +720,7 @@ bool Decl::isWeakImported() const {
   if (!canBeWeakImported(IsDefinition))
     return false;
 
-  for (const auto *A : attrs()) {
+  for (const auto *A : getMostRecentDecl()->attrs()) {
     if (isa<WeakImportAttr>(A))
       return true;
 

clang/lib/AST/ExprConstant.cpp

@@ -1978,18 +1978,11 @@ static bool HasSameBase(const LValue &A, const LValue &B) {
     return false;
 
   if (A.getLValueBase().getOpaqueValue() !=
-      B.getLValueBase().getOpaqueValue()) {
-    const Decl *ADecl = GetLValueBaseDecl(A);
-    if (!ADecl)
-      return false;
-    const Decl *BDecl = GetLValueBaseDecl(B);
-    if (!BDecl || ADecl->getCanonicalDecl() != BDecl->getCanonicalDecl())
-      return false;
-  }
+      B.getLValueBase().getOpaqueValue())
+    return false;
 
-  return IsGlobalLValue(A.getLValueBase()) ||
-         (A.getLValueCallIndex() == B.getLValueCallIndex() &&
-          A.getLValueVersion() == B.getLValueVersion());
+  return A.getLValueCallIndex() == B.getLValueCallIndex() &&
+         A.getLValueVersion() == B.getLValueVersion();
 }
 
 static void NoteLValueLocation(EvalInfo &Info, APValue::LValueBase Base) {
@@ -3158,7 +3151,8 @@ static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
 
   // If we're currently evaluating the initializer of this declaration, use that
   // in-flight value.
-  if (Info.EvaluatingDecl.dyn_cast<const ValueDecl*>() == VD) {
+  if (declaresSameEntity(Info.EvaluatingDecl.dyn_cast<const ValueDecl *>(),
+                         VD)) {
     Result = Info.EvaluatingDeclValue;
     return true;
   }

clang/lib/CodeGen/CGExprConstant.cpp

@@ -1877,6 +1877,10 @@ ConstantLValue
 ConstantLValueEmitter::tryEmitBase(const APValue::LValueBase &base) {
   // Handle values.
   if (const ValueDecl *D = base.dyn_cast<const ValueDecl*>()) {
+    // The constant always points to the canonical declaration. We want to look
+    // at properties of the most recent declaration at the point of emission.
+    D = cast<ValueDecl>(D->getMostRecentDecl());
+
     if (D->hasAttr<WeakRefAttr>())
       return CGM.GetWeakRefReference(D).getPointer();
 

clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp

@@ -24,11 +24,10 @@ constexpr double &ni3; // expected-error {{declaration of reference variable 'ni
 
 constexpr int nc1 = i; // expected-error {{constexpr variable 'nc1' must be initialized by a constant expression}} expected-note {{read of non-const variable 'i' is not allowed in a constant expression}}
 constexpr C nc2 = C(); // expected-error {{cannot have non-literal type 'const C'}}
-int &f(); // expected-note {{declared here}}
+int &f(); // expected-note 2{{declared here}}
 constexpr int &nc3 = f(); // expected-error {{constexpr variable 'nc3' must be initialized by a constant expression}} expected-note {{non-constexpr function 'f' cannot be used in a constant expression}}
 constexpr int nc4(i); // expected-error {{constexpr variable 'nc4' must be initialized by a constant expression}} expected-note {{read of non-const variable 'i' is not allowed in a constant expression}}
 constexpr C nc5((C())); // expected-error {{cannot have non-literal type 'const C'}}
-int &f(); // expected-note {{here}}
 constexpr int &nc6(f()); // expected-error {{constexpr variable 'nc6' must be initialized by a constant expression}} expected-note {{non-constexpr function 'f'}}
 
 struct pixel {

clang/test/CodeGenCXX/weak-external.cpp

@@ -64,3 +64,15 @@ class _LIBCPP_EXCEPTION_ABI runtime_error
 void dummysymbol() {
   throw(std::runtime_error("string"));
 }
+
+namespace not_weak_on_first {
+  int func();
+  // CHECK: {{.*}} extern_weak {{.*}} @_ZN17not_weak_on_first4funcEv(
+  int func() __attribute__ ((weak));
+
+  typedef int (*FuncT)();
+
+  extern const FuncT table[] = {
+      func,
+  };
+}

clang/test/OpenMP/ordered_messages.cpp

@@ -16,6 +16,9 @@ void xxx(int argc) {
 }
 
 int foo();
+#if __cplusplus >= 201103L
+// expected-note@-2 {{declared here}}
+#endif
 
 template <class T>
 T foo() {
@@ -176,7 +179,7 @@ T foo() {
 
 int foo() {
 #if __cplusplus >= 201103L
-// expected-note@-2 2 {{declared here}}
+// expected-note@-2 {{declared here}}
 #endif
 int k;
   #pragma omp for ordered