Revert 363295, it caused PR42276. Also revert follow-ups 363337, 363340.

Revert 363340 "Remove unused SK_LValueToRValue initialization step."
Revert 363337 "PR23833, DR2140: an lvalue-to-rvalue conversion on a glvalue of type"
Revert 363295 "C++ DR712 and others: handle non-odr-use resulting from an lvalue-to-rvalue conversion applied to a member access or similar not-quite-trivial lvalue expression."

llvm-svn: 363352

2 files changed, 51 insertions, 131 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index a561b045f9a..d444a35be86 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -635,10 +635,8 @@ 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;
-  Res = ImplicitCastExpr::Create(Context, T, CK, E, nullptr, VK_RValue);
+  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
@@ -15808,32 +15806,6 @@ QualType Sema::getCapturedDeclRefType(VarDecl *Var, SourceLocation Loc) {
   return DeclRefType;
 }
 
-namespace {
-// Helper to copy the template arguments from a DeclRefExpr or MemberExpr.
-// The produced TemplateArgumentListInfo* points to data stored within this
-// object, so should only be used in contexts where the pointer will not be
-// used after the CopiedTemplateArgs object is destroyed.
-class CopiedTemplateArgs {
-  bool HasArgs;
-  TemplateArgumentListInfo TemplateArgStorage;
-public:
-  template<typename RefExpr>
-  CopiedTemplateArgs(RefExpr *E) : HasArgs(E->hasExplicitTemplateArgs()) {
-    if (HasArgs)
-      E->copyTemplateArgumentsInto(TemplateArgStorage);
-  }
-  operator TemplateArgumentListInfo*()
-#ifdef __has_cpp_attribute
-#if __has_cpp_attribute(clang::lifetimebound)
-  [[clang::lifetimebound]]
-#endif
-#endif
-  {
-    return HasArgs ? &TemplateArgStorage : nullptr;
-  }
-};
-}
-
 /// Walk the set of potential results of an expression and mark them all as
 /// non-odr-uses if they satisfy the side-conditions of the NonOdrUseReason.
 ///
@@ -15925,11 +15897,16 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
 
     // Rebuild as a non-odr-use DeclRefExpr.
     MarkNotOdrUsed();
+    TemplateArgumentListInfo TemplateArgStorage, *TemplateArgs = nullptr;
+    if (DRE->hasExplicitTemplateArgs()) {
+      DRE->copyTemplateArgumentsInto(TemplateArgStorage);
+      TemplateArgs = &TemplateArgStorage;
+    }
     return DeclRefExpr::Create(
         S.Context, DRE->getQualifierLoc(), DRE->getTemplateKeywordLoc(),
         DRE->getDecl(), DRE->refersToEnclosingVariableOrCapture(),
         DRE->getNameInfo(), DRE->getType(), DRE->getValueKind(),
-        DRE->getFoundDecl(), CopiedTemplateArgs(DRE), NOUR);
+        DRE->getFoundDecl(), TemplateArgs, NOUR);
   }
 
   case Expr::FunctionParmPackExprClass: {
@@ -15947,107 +15924,52 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
     break;
   }
 
+  // FIXME: Implement these.
   //   -- If e is a subscripting operation with an array operand...
-  case Expr::ArraySubscriptExprClass: {
-    auto *ASE = cast<ArraySubscriptExpr>(E);
-    Expr *OldBase = ASE->getBase()->IgnoreImplicit();
-    if (!OldBase->getType()->isArrayType())
-      break;
-    ExprResult Base = Rebuild(OldBase);
-    if (!Base.isUsable())
-      return Base;
-    Expr *LHS = ASE->getBase() == ASE->getLHS() ? Base.get() : ASE->getLHS();
-    Expr *RHS = ASE->getBase() == ASE->getRHS() ? Base.get() : ASE->getRHS();
-    SourceLocation LBracketLoc = ASE->getBeginLoc(); // FIXME: Not stored.
-    return S.ActOnArraySubscriptExpr(nullptr, LHS, LBracketLoc, RHS,
-                                     ASE->getRBracketLoc());
-  }
+  //   -- If e is a class member access expression [...] naming a non-static
+  //      data member...
 
+  //   -- If e is a class member access expression naming a static data member,
+  //      ...
   case Expr::MemberExprClass: {
     auto *ME = cast<MemberExpr>(E);
-    // -- If e is a class member access expression [...] naming a non-static
-    //    data member...
-    if (isa<FieldDecl>(ME->getMemberDecl())) {
-      ExprResult Base = Rebuild(ME->getBase());
-      if (!Base.isUsable())
-        return Base;
-      return MemberExpr::Create(
-          S.Context, Base.get(), ME->isArrow(), ME->getOperatorLoc(),
-          ME->getQualifierLoc(), ME->getTemplateKeywordLoc(),
-          ME->getMemberDecl(), ME->getFoundDecl(), ME->getMemberNameInfo(),
-          CopiedTemplateArgs(ME), ME->getType(), ME->getValueKind(),
-          ME->getObjectKind(), ME->isNonOdrUse());
-    }
-
     if (ME->getMemberDecl()->isCXXInstanceMember())
+      // FIXME: Recurse to the left-hand side.
       break;
 
-    // -- If e is a class member access expression naming a static data member,
-    //    ...
     if (ME->isNonOdrUse() || IsPotentialResultOdrUsed(ME->getMemberDecl()))
       break;
 
     // Rebuild as a non-odr-use MemberExpr.
     MarkNotOdrUsed();
+    TemplateArgumentListInfo TemplateArgStorage, *TemplateArgs = nullptr;
+    if (ME->hasExplicitTemplateArgs()) {
+      ME->copyTemplateArgumentsInto(TemplateArgStorage);
+      TemplateArgs = &TemplateArgStorage;
+    }
     return MemberExpr::Create(
         S.Context, ME->getBase(), ME->isArrow(), ME->getOperatorLoc(),
         ME->getQualifierLoc(), ME->getTemplateKeywordLoc(), ME->getMemberDecl(),
-        ME->getFoundDecl(), ME->getMemberNameInfo(), CopiedTemplateArgs(ME),
+        ME->getFoundDecl(), ME->getMemberNameInfo(), TemplateArgs,
         ME->getType(), ME->getValueKind(), ME->getObjectKind(), NOUR);
     return ExprEmpty();
   }
 
-  case Expr::BinaryOperatorClass: {
-    auto *BO = cast<BinaryOperator>(E);
-    Expr *LHS = BO->getLHS();
-    Expr *RHS = BO->getRHS();
-    // -- If e is a pointer-to-member expression of the form e1 .* e2 ...
-    if (BO->getOpcode() == BO_PtrMemD) {
-      ExprResult Sub = Rebuild(LHS);
-      if (!Sub.isUsable())
-        return Sub;
-      LHS = Sub.get();
-    //   -- If e is a comma expression, ...
-    } else if (BO->getOpcode() == BO_Comma) {
-      ExprResult Sub = Rebuild(RHS);
-      if (!Sub.isUsable())
-        return Sub;
-      RHS = Sub.get();
-    } else {
-      break;
-    }
-    return S.BuildBinOp(nullptr, BO->getOperatorLoc(), BO->getOpcode(),
-                        LHS, RHS);
-  }
+  // FIXME: Implement this.
+  //   -- If e is a pointer-to-member expression of the form e1 .* e2 ...
 
   //   -- If e has the form (e1)...
   case Expr::ParenExprClass: {
-    auto *PE = cast<ParenExpr>(E);
+    auto *PE = dyn_cast<ParenExpr>(E);
     ExprResult Sub = Rebuild(PE->getSubExpr());
     if (!Sub.isUsable())
       return Sub;
     return S.ActOnParenExpr(PE->getLParen(), PE->getRParen(), Sub.get());
   }
 
+  // FIXME: Implement these.
   //   -- If e is a glvalue conditional expression, ...
-  // We don't apply this to a binary conditional operator. FIXME: Should we?
-  case Expr::ConditionalOperatorClass: {
-    auto *CO = cast<ConditionalOperator>(E);
-    ExprResult LHS = Rebuild(CO->getLHS());
-    if (LHS.isInvalid())
-      return ExprError();
-    ExprResult RHS = Rebuild(CO->getRHS());
-    if (RHS.isInvalid())
-      return ExprError();
-    if (!LHS.isUsable() && !RHS.isUsable())
-      return ExprEmpty();
-    if (!LHS.isUsable())
-      LHS = CO->getLHS();
-    if (!RHS.isUsable())
-      RHS = CO->getRHS();
-    return S.ActOnConditionalOp(CO->getQuestionLoc(), CO->getColonLoc(),
-                                CO->getCond(), LHS.get(), RHS.get());
-  }
+  //   -- If e is a comma expression, ...
 
   // [Clang extension]
   //   -- If e has the form __extension__ e1...
@@ -16066,7 +15988,7 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
   //   -- If e has the form _Generic(...), the set of potential results is the
   //      union of the sets of potential results of the associated expressions.
   case Expr::GenericSelectionExprClass: {
-    auto *GSE = cast<GenericSelectionExpr>(E);
+    auto *GSE = dyn_cast<GenericSelectionExpr>(E);
 
     SmallVector<Expr *, 4> AssocExprs;
     bool AnyChanged = false;
@@ -16094,7 +16016,7 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
   //      results is the union of the sets of potential results of the
   //      second and third subexpressions.
   case Expr::ChooseExprClass: {
-    auto *CE = cast<ChooseExpr>(E);
+    auto *CE = dyn_cast<ChooseExpr>(E);
 
     ExprResult LHS = Rebuild(CE->getLHS());
     if (LHS.isInvalid())
@@ -16117,38 +16039,13 @@ static ExprResult rebuildPotentialResultsAsNonOdrUsed(Sema &S, Expr *E,
 
   // Step through non-syntactic nodes.
   case Expr::ConstantExprClass: {
-    auto *CE = cast<ConstantExpr>(E);
+    auto *CE = dyn_cast<ConstantExpr>(E);
     ExprResult Sub = Rebuild(CE->getSubExpr());
     if (!Sub.isUsable())
       return Sub;
     return ConstantExpr::Create(S.Context, Sub.get());
   }
 
-  // We could mostly rely on the recursive rebuilding to rebuild implicit
-  // casts, but not at the top level, so rebuild them here.
-  case Expr::ImplicitCastExprClass: {
-    auto *ICE = cast<ImplicitCastExpr>(E);
-    // Only step through the narrow set of cast kinds we expect to encounter.
-    // Anything else suggests we've left the region in which potential results
-    // can be found.
-    switch (ICE->getCastKind()) {
-    case CK_NoOp:
-    case CK_DerivedToBase:
-    case CK_UncheckedDerivedToBase: {
-      ExprResult Sub = Rebuild(ICE->getSubExpr());
-      if (!Sub.isUsable())
-        return Sub;
-      CXXCastPath Path(ICE->path());
-      return S.ImpCastExprToType(Sub.get(), ICE->getType(), ICE->getCastKind(),
-                                 ICE->getValueKind(), &Path);
-    }
-
-    default:
-      break;
-    }
-    break;
-  }
-
   default:
     break;
   }
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index d5ef5eddf3e..1a1d9347985 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -3282,6 +3282,7 @@ void InitializationSequence::Step::Destroy() {
   case SK_QualificationConversionXValue:
   case SK_QualificationConversionLValue:
   case SK_AtomicConversion:
+  case SK_LValueToRValue:
   case SK_ListInitialization:
   case SK_UnwrapInitList:
   case SK_RewrapInitList:
@@ -3465,6 +3466,15 @@ void InitializationSequence::AddAtomicConversionStep(QualType Ty) {
   Steps.push_back(S);
 }
 
+void InitializationSequence::AddLValueToRValueStep(QualType Ty) {
+  assert(!Ty.hasQualifiers() && "rvalues may not have qualifiers");
+
+  Step S;
+  S.Kind = SK_LValueToRValue;
+  S.Type = Ty;
+  Steps.push_back(S);
+}
+
 void InitializationSequence::AddConversionSequenceStep(
     const ImplicitConversionSequence &ICS, QualType T,
     bool TopLevelOfInitList) {
@@ -7495,6 +7505,7 @@ ExprResult InitializationSequence::Perform(Sema &S,
   case SK_QualificationConversionXValue:
   case SK_QualificationConversionRValue:
   case SK_AtomicConversion:
+  case SK_LValueToRValue:
   case SK_ConversionSequence:
   case SK_ConversionSequenceNoNarrowing:
   case SK_ListInitialization:
@@ -7766,6 +7777,14 @@ ExprResult InitializationSequence::Perform(Sema &S,
       break;
     }
 
+    case SK_LValueToRValue: {
+      assert(CurInit.get()->isGLValue() && "cannot load from a prvalue");
+      CurInit = ImplicitCastExpr::Create(S.Context, Step->Type,
+                                         CK_LValueToRValue, CurInit.get(),
+                                         /*BasePath=*/nullptr, VK_RValue);
+      break;
+    }
+
     case SK_ConversionSequence:
     case SK_ConversionSequenceNoNarrowing: {
       if (const auto *FromPtrType =
@@ -8987,6 +9006,10 @@ void InitializationSequence::dump(raw_ostream &OS) const {
       OS << "non-atomic-to-atomic conversion";
       break;
 
+    case SK_LValueToRValue:
+      OS << "load (lvalue to rvalue)";
+      break;
+
     case SK_ConversionSequence:
       OS << "implicit conversion sequence (";
       S->ICS->dump(); // FIXME: use OS