Revert r345562: "PR23833, DR2140: an lvalue-to-rvalue conversion on a glvalue of type"

This exposes a (known) CodeGen bug: it can't cope with emitting lvalue
expressions that denote non-odr-used but usable-in-constant-expression
variables. See PR39528 for a testcase.

Reverted for now until that issue can be fixed.

llvm-svn: 346065

10 files changed, 20 insertions, 81 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 4f7f807a84e..8b512815e81 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1816,11 +1816,6 @@ ImplicitCastExpr *ImplicitCastExpr::Create(const ASTContext &C, QualType T,
   void *Buffer =
       C.Allocate(totalSizeToAlloc<CastExpr::BasePathSizeTy, CXXBaseSpecifier *>(
           PathSize ? 1 : 0, PathSize));
-  // Per C++ [conv.lval]p3, lvalue-to-rvalue conversions on class and
-  // std::nullptr_t have special semantics not captured by CK_LValueToRValue.
-  assert((Kind != CK_LValueToRValue ||
-          !(T->isNullPtrType() || T->getAsCXXRecordDecl())) &&
-         "invalid type for lvalue-to-rvalue conversion");
   ImplicitCastExpr *E =
     new (Buffer) ImplicitCastExpr(T, Kind, Operand, PathSize, VK);
   if (PathSize)
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 0bbf3a6c561..42481939fa1 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1300,8 +1300,7 @@ static bool isSimpleZero(const Expr *E, CodeGenFunction &CGF) {
   // (int*)0 - Null pointer expressions.
   if (const CastExpr *ICE = dyn_cast<CastExpr>(E))
     return ICE->getCastKind() == CK_NullToPointer &&
-           CGF.getTypes().isPointerZeroInitializable(E->getType()) &&
-           !E->HasSideEffects(CGF.getContext());
+        CGF.getTypes().isPointerZeroInitializable(E->getType());
   // '\0'
   if (const CharacterLiteral *CL = dyn_cast<CharacterLiteral>(E))
     return CL->getValue() == 0;
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index c77f1bab5b1..519606e8214 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2072,14 +2072,14 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
 
   case CK_NullToPointer:
     if (MustVisitNullValue(E))
-      CGF.EmitIgnoredExpr(E);
+      (void) Visit(E);
 
     return CGF.CGM.getNullPointer(cast<llvm::PointerType>(ConvertType(DestTy)),
                               DestTy);
 
   case CK_NullToMemberPointer: {
     if (MustVisitNullValue(E))
-      CGF.EmitIgnoredExpr(E);
+      (void) Visit(E);
 
     const MemberPointerType *MPT = CE->getType()->getAs<MemberPointerType>();
     return CGF.CGM.getCXXABI().EmitNullMemberPointer(MPT);
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index d7fc1aa04dd..a7dc08248eb 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -623,11 +623,8 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   if (E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
     Cleanup.setExprNeedsCleanups(true);
 
-  // C++ [conv.lval]p3:
-  //   If T is cv std::nullptr_t, the result is a null pointer constant.
-  CastKind CK = T->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
-  ExprResult Res =
-      ImplicitCastExpr::Create(Context, T, CK, E, nullptr, VK_RValue);
+  ExprResult Res = ImplicitCastExpr::Create(Context, T, CK_LValueToRValue, E,
+                                            nullptr, VK_RValue);
 
   // C11 6.3.2.1p2:
   //   ... if the lvalue has atomic type, the value has the non-atomic version
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 0cfac997199..1e4d12d20cd 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -7644,13 +7644,9 @@ InitializationSequence::Perform(Sema &S,
 
     case SK_LValueToRValue: {
       assert(CurInit.get()->isGLValue() && "cannot load from a prvalue");
-      // C++ [conv.lval]p3:
-      //   If T is cv std::nullptr_t, the result is a null pointer constant.
-      CastKind CK =
-          Step->Type->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
-      CurInit =
-          ImplicitCastExpr::Create(S.Context, Step->Type, CK, CurInit.get(),
-                                   /*BasePath=*/nullptr, VK_RValue);
+      CurInit = ImplicitCastExpr::Create(S.Context, Step->Type,
+                                         CK_LValueToRValue, CurInit.get(),
+                                         /*BasePath=*/nullptr, VK_RValue);
       break;
     }
 
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
index 74345b5eba8..fb13e89b5fa 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -379,6 +379,7 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
       case CK_BitCast:
       case CK_AddressSpaceConversion:
       case CK_BooleanToSignedIntegral:
+      case CK_NullToPointer:
       case CK_IntegralToPointer:
       case CK_PointerToIntegral: {
         SVal V = state->getSVal(Ex, LCtx);
@@ -501,12 +502,6 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
         Bldr.generateNode(CastE, Pred, state);
         continue;
       }
-      case CK_NullToPointer: {
-        SVal V = svalBuilder.makeNull();
-        state = state->BindExpr(CastE, LCtx, V);
-        Bldr.generateNode(CastE, Pred, state);
-        continue;
-      }
       case CK_NullToMemberPointer: {
         SVal V = svalBuilder.getMemberPointer(nullptr);
         state = state->BindExpr(CastE, LCtx, V);
diff --git a/clang/test/Analysis/nullptr.cpp b/clang/test/Analysis/nullptr.cpp
index e9b975c148a..38e099b7fbd 100644
--- a/clang/test/Analysis/nullptr.cpp
+++ b/clang/test/Analysis/nullptr.cpp
@@ -128,10 +128,18 @@ void shouldNotCrash() {
   decltype(nullptr) p; // expected-note{{'p' declared without an initial value}}
   if (getSymbol()) // expected-note   {{Assuming the condition is false}}
                    // expected-note@-1{{Taking false branch}}
+                   // expected-note@-2{{Assuming the condition is false}}
+                   // expected-note@-3{{Taking false branch}}
+                   // expected-note@-4{{Assuming the condition is true}}
+                   // expected-note@-5{{Taking true branch}}
+    invokeF(p); // expected-warning{{1st function call argument is an uninitialized value}}
+                // expected-note@-1{{1st function call argument is an uninitialized value}}
+  if (getSymbol()) // expected-note   {{Assuming the condition is false}}
+                   // expected-note@-1{{Taking false branch}}
                    // expected-note@-2{{Assuming the condition is true}}
                    // expected-note@-3{{Taking true branch}}
-    invokeF(p);    // expected-note   {{Calling 'invokeF'}}
-                   // expected-note@-1{{Passing null pointer value via 1st parameter 'x'}}
+    invokeF(nullptr); // expected-note   {{Calling 'invokeF'}}
+                      // expected-note@-1{{Passing null pointer value via 1st parameter 'x'}}
   if (getSymbol()) {  // expected-note  {{Assuming the condition is true}}
                       // expected-note@-1{{Taking true branch}}
     X *xx = Type().x; // expected-note   {{Null pointer value stored to field 'x'}}
diff --git a/clang/test/CXX/drs/dr21xx.cpp b/clang/test/CXX/drs/dr21xx.cpp
index b111529b09f..2522ff7dbde 100644
--- a/clang/test/CXX/drs/dr21xx.cpp
+++ b/clang/test/CXX/drs/dr21xx.cpp
@@ -19,16 +19,6 @@ namespace dr2120 { // dr2120: 7
   static_assert(!__is_standard_layout(E), "");
 }
 
-namespace dr2140 { // dr2140: 8
-#if __cplusplus >= 201103L
-  union U { int a; decltype(nullptr) b; };
-  constexpr int *test(U u) {
-    return u.b;
-  }
-  static_assert(!test({123}), "u.b should be valid even when b is inactive");
-#endif
-}
-
 namespace dr2180 { // dr2180: yes
   class A {
     A &operator=(const A &); // expected-note 0-2{{here}}
diff --git a/clang/test/CodeGenCXX/nullptr.cpp b/clang/test/CodeGenCXX/nullptr.cpp
index 222e5e5803c..e93f7061bdd 100644
--- a/clang/test/CodeGenCXX/nullptr.cpp
+++ b/clang/test/CodeGenCXX/nullptr.cpp
@@ -22,44 +22,3 @@ void g() {
 const std::type_info& f2() {
   return typeid(nullptr_t);
 }
-
-union U {
-  int n;
-  nullptr_t b;
-};
-// CHECK-LABEL: define {{.*}}pr23833_a
-// CHECK: store
-// CHECK: load
-// CHECK-NOT: load
-// CHECK: ret i1 false
-bool pr23833_a(U &u) { return u.b; }
-
-// CHECK-LABEL: define {{.*}}pr23833_b
-// CHECK: store
-// CHECK: load
-// CHECK-NOT: load
-// CHECK: ret i8* null
-nullptr_t pr23833_b(nullptr_t &n) { return n; }
-
-struct X1 { operator int*(); };
-struct X2 { operator const nullptr_t&(); };
-
-// CHECK-LABEL: define {{.*}}pr23833_c
-// CHECK: call {{.*}}X1
-// CHECK: call {{.*}}X2
-// CHECK-NOT: load
-// CHECK: ret i32
-int pr23833_c() {
-  return X1() != X2();
-}
-
-// CHECK-LABEL: define {{.*}}pr23833_d
-// CHECK: call {{.*}}X2
-// CHECK-NOT: load
-// CHECK: store
-// CHECK: load
-// CHECK: ret i32*
-int *pr23833_d() {
-  int *p = X2();
-  return p;
-}
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 69b0b9d0753..460978260f1 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -12655,7 +12655,7 @@ and <I>POD class</I></td>
     <td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2140">2140</a></td>
     <td>CD4</td>
     <td>Lvalue-to-rvalue conversion of <TT>std::nullptr_t</TT></td>
-    <td class="svn" align="center">SVN</td>
+    <td class="none" align="center">Unknown</td>
   </tr>
   <tr id="2141">
     <td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2141">2141</a></td>