commit 7b0332389afd705f46b02fcf87ec3414b8dece34
Author: Nico Weber <thakis@chromium.org>
Date:   Fri Sep 4 10:13:28 2020 -0400

    Revert "Canonicalize declaration pointers when forming APValues."
    
    This reverts commit e6393ee813178e9d3306b8e3c6949a4f32f8a2cb.
    It breaks Wunreachable for weak attributes, see
    http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20200831/336645.html

diff --git a/clang/include/clang/AST/APValue.h b/clang/include/clang/AST/APValue.h
index 485e6c2602c..87e4bd7f84c 100644
--- a/clang/include/clang/AST/APValue.h
+++ b/clang/include/clang/AST/APValue.h
@@ -174,7 +174,6 @@ public:
       return !(LHS == RHS);
     }
     friend llvm::hash_code hash_value(const LValueBase &Base);
-    friend struct llvm::DenseMapInfo<LValueBase>;
 
   private:
     PtrTy Ptr;
@@ -202,7 +201,8 @@ public:
 
   public:
     LValuePathEntry() : Value() {}
-    LValuePathEntry(BaseOrMemberType BaseOrMember);
+    LValuePathEntry(BaseOrMemberType BaseOrMember)
+        : Value{reinterpret_cast<uintptr_t>(BaseOrMember.getOpaqueValue())} {}
     static LValuePathEntry ArrayIndex(uint64_t Index) {
       LValuePathEntry Result;
       Result.Value = Index;
diff --git a/clang/lib/AST/APValue.cpp b/clang/lib/AST/APValue.cpp
index 7531229654c..2a8834b4db0 100644
--- a/clang/lib/AST/APValue.cpp
+++ b/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 ? cast<ValueDecl>(P->getCanonicalDecl()) : nullptr), Local{I, V} {}
+    : Ptr(P), Local{I, V} {}
 APValue::LValueBase::LValueBase(const Expr *P, unsigned I, unsigned V)
     : Ptr(P), Local{I, V} {}
 
@@ -82,19 +82,13 @@ bool operator==(const APValue::LValueBase &LHS,
                 const APValue::LValueBase &RHS) {
   if (LHS.Ptr != RHS.Ptr)
     return false;
-  if (LHS.is<TypeInfoLValue>() || LHS.is<DynamicAllocLValue>())
+  if (LHS.is<TypeInfoLValue>())
     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;
@@ -119,16 +113,14 @@ APValue::LValueBase::operator bool () const {
 
 clang::APValue::LValueBase
 llvm::DenseMapInfo<clang::APValue::LValueBase>::getEmptyKey() {
-  clang::APValue::LValueBase B;
-  B.Ptr = DenseMapInfo<const ValueDecl*>::getEmptyKey();
-  return B;
+  return clang::APValue::LValueBase(
+      DenseMapInfo<const ValueDecl*>::getEmptyKey());
 }
 
 clang::APValue::LValueBase
 llvm::DenseMapInfo<clang::APValue::LValueBase>::getTombstoneKey() {
-  clang::APValue::LValueBase B;
-  B.Ptr = DenseMapInfo<const ValueDecl*>::getTombstoneKey();
-  return B;
+  return clang::APValue::LValueBase(
+      DenseMapInfo<const ValueDecl*>::getTombstoneKey());
 }
 
 namespace clang {
@@ -765,10 +757,8 @@ 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 ? cast<ValueDecl>(Member->getCanonicalDecl()) : nullptr);
+  MPD->MemberAndIsDerivedMember.setPointer(Member);
   MPD->MemberAndIsDerivedMember.setInt(IsDerivedMember);
   MPD->resizePath(Path.size());
-  for (unsigned I = 0; I != Path.size(); ++I)
-    MPD->getPath()[I] = Path[I]->getCanonicalDecl();
+  memcpy(MPD->getPath(), Path.data(), Path.size()*sizeof(const CXXRecordDecl*));
 }
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 8e43b62662e..e8f132dd480 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -1978,11 +1978,18 @@ static bool HasSameBase(const LValue &A, const LValue &B) {
     return false;
 
   if (A.getLValueBase().getOpaqueValue() !=
-      B.getLValueBase().getOpaqueValue())
-    return false;
+      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;
+  }
 
-  return A.getLValueCallIndex() == B.getLValueCallIndex() &&
-         A.getLValueVersion() == B.getLValueVersion();
+  return IsGlobalLValue(A.getLValueBase()) ||
+         (A.getLValueCallIndex() == B.getLValueCallIndex() &&
+          A.getLValueVersion() == B.getLValueVersion());
 }
 
 static void NoteLValueLocation(EvalInfo &Info, APValue::LValueBase Base) {
@@ -3101,8 +3108,7 @@ static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
 
   // If we're currently evaluating the initializer of this declaration, use that
   // in-flight value.
-  if (declaresSameEntity(Info.EvaluatingDecl.dyn_cast<const ValueDecl *>(),
-                         VD)) {
+  if (Info.EvaluatingDecl.dyn_cast<const ValueDecl*>() == VD) {
     Result = Info.EvaluatingDeclValue;
     return true;
   }
diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp
index 3720b277af7..8d51dbde717 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p9.cpp
@@ -24,10 +24,11 @@ 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 2{{declared here}}
+int &f(); // expected-note {{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 {
diff --git a/clang/test/OpenMP/ordered_messages.cpp b/clang/test/OpenMP/ordered_messages.cpp
index 8a3a86443eb..f6b9dbd6d27 100644
--- a/clang/test/OpenMP/ordered_messages.cpp
+++ b/clang/test/OpenMP/ordered_messages.cpp
@@ -16,9 +16,6 @@ void xxx(int argc) {
 }
 
 int foo();
-#if __cplusplus >= 201103L
-// expected-note@-2 {{declared here}}
-#endif
 
 template <class T>
 T foo() {
@@ -179,7 +176,7 @@ T foo() {
 
 int foo() {
 #if __cplusplus >= 201103L
-// expected-note@-2 {{declared here}}
+// expected-note@-2 2 {{declared here}}
 #endif
 int k;
   #pragma omp for ordered