DR1295 and cleanup for P0135R1: Make our initialization code more directly

mirror the description in the standard. Per DR1295, this means that binding a
const / rvalue reference to a bit-field no longer "binds directly", and per
P0135R1, this means that we materialize a temporary in reference binding
after adjusting cv-qualifiers and before performing a derived-to-base cast.

In C++11 onwards, this should have fixed the last case where we would
materialize a temporary of the wrong type (with a subobject adjustment inside
the MaterializeTemporaryExpr instead of outside), but we still have to deal
with that possibility in C++98, unless we want to start using xvalues to
represent materialized temporaries there too.

llvm-svn: 289250

8 files changed, 61 insertions, 17 deletions

diff --git a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5-examples.cpp b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5-examples.cpp
index be1113d47e3..052349c8e2e 100644
--- a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5-examples.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5-examples.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -ast-dump %s 2>&1 | FileCheck %s
 
-// CHECK: example0
+// CHECK-LABEL: example0
 void example0() {
   double d = 2.0;
   // CHECK: VarDecl{{.*}}rd 'double &'
@@ -14,14 +14,15 @@ void example0() {
 struct A { };
 struct B : A { } b;
 
-// CHECK: example1
+// CHECK-LABEL: example1
 void example1() {
   // CHECK: VarDecl{{.*}}ra 'struct A &'
   // CHECK: ImplicitCastExpr{{.*}}'struct A' lvalue <DerivedToBase (A)>
   A &ra = b;
   // CHECK: VarDecl{{.*}}rca 'const struct A &'
-  // CHECK: ImplicitCastExpr{{.*}}'const struct A' lvalue <NoOp>
-  // CHECK: ImplicitCastExpr{{.*}}'struct A' lvalue <DerivedToBase (A)>
+  // CHECK: ImplicitCastExpr{{.*}}'const struct A' lvalue <DerivedToBase (A)>
+  // CHECK-NOT: MaterializeTemporaryExpr
+  // CHECK: ImplicitCastExpr{{.*}}'const struct B' lvalue <NoOp>
   const A& rca = b;
 }
 
@@ -31,21 +32,23 @@ struct X {
   operator B();
 } x;
 
-// CHECK: example2
+// CHECK-LABEL: example2
 void example2() {
   // CHECK: VarDecl{{.*}}rca 'const struct A &'
-  // CHECK: ImplicitCastExpr{{.*}}'const struct A' <NoOp>
-  // CHECK: ImplicitCastExpr{{.*}}'struct A' <DerivedToBase (A)>
+  // CHECK: ImplicitCastExpr{{.*}}'const struct A' lvalue <DerivedToBase (A)>
+  // CHECK: MaterializeTemporaryExpr{{.*}}'const struct B'
+  // CHECK: ImplicitCastExpr{{.*}}'const struct B' <NoOp>
   // CHECK: CallExpr{{.*}}B
   const A &rca = f(); 
   // CHECK: VarDecl{{.*}}r 'const struct A &'
-  // CHECK: ImplicitCastExpr{{.*}}'const struct A' <NoOp>
-  // CHECK: ImplicitCastExpr{{.*}}'struct A' <DerivedToBase (A)>
+  // CHECK: ImplicitCastExpr{{.*}}'const struct A' lvalue <DerivedToBase (A)>
+  // CHECK: MaterializeTemporaryExpr{{.*}}'const struct B'
+  // CHECK: ImplicitCastExpr{{.*}}'const struct B' <NoOp>
   // CHECK: CXXMemberCallExpr{{.*}}'struct B'
   const A& r = x;
 }
 
-// CHECK: example3
+// CHECK-LABEL: example3
 void example3() {
   // CHECK: VarDecl{{.*}}rcd2 'const double &'
   // CHECK: ImplicitCastExpr{{.*}} <IntegralToFloating>
diff --git a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5.cpp b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5.cpp
index 263f661208c..e775e8f0e3c 100644
--- a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.ref/p5.cpp
@@ -41,7 +41,7 @@ namespace PR6066 {
 
 namespace test3 {
   struct A {
-    unsigned bitX : 4; // expected-note 4 {{bit-field is declared here}}
+    unsigned bitX : 4; // expected-note 3 {{bit-field is declared here}}
     unsigned bitY : 4; // expected-note {{bit-field is declared here}}
     unsigned var;
 
@@ -50,7 +50,7 @@ namespace test3 {
 
   void test(A *a) {
     unsigned &t0 = a->bitX; // expected-error {{non-const reference cannot bind to bit-field 'bitX'}}
-    unsigned &t1 = (unsigned&) a->bitX; // expected-error {{non-const reference cannot bind to bit-field 'bitX'}}
+    unsigned &t1 = (unsigned&) a->bitX; // expected-error {{C-style cast from bit-field lvalue to reference type 'unsigned int &'}}
     unsigned &t2 = const_cast<unsigned&>(a->bitX); // expected-error {{const_cast from bit-field lvalue to reference type 'unsigned int &'}}
     unsigned &t3 = (a->foo(), a->bitX); // expected-error {{non-const reference cannot bind to bit-field 'bitX'}}
     unsigned &t4 = (a->var ? a->bitX : a->bitY); // expected-error {{non-const reference cannot bind to bit-field}}
diff --git a/clang/test/CXX/drs/dr12xx.cpp b/clang/test/CXX/drs/dr12xx.cpp
index c4f980a87dd..72d8d683ab7 100644
--- a/clang/test/CXX/drs/dr12xx.cpp
+++ b/clang/test/CXX/drs/dr12xx.cpp
@@ -3,8 +3,6 @@
 // RUN: %clang_cc1 -std=c++14 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 // RUN: %clang_cc1 -std=c++1z %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
 
-// expected-no-diagnostics
-
 namespace dr1213 { // dr1213: 4.0
 #if __cplusplus >= 201103L
   using T = int[3];
@@ -27,3 +25,29 @@ struct Derived : Base {
   virtual Incomplete *meow();
 };
 } // dr1250
+
+namespace dr1295 {  // dr1295: 4.0
+  struct X {
+    unsigned bitfield : 4;
+  };
+
+  X x = {1};
+
+  unsigned const &r1 = static_cast<X &&>(x).bitfield; // expected-error 0-1{{C++11}}
+  unsigned const &r2 = static_cast<unsigned &&>(x.bitfield); // expected-error 0-1{{C++11}}
+
+  template<unsigned &r> struct Y {};
+  Y<x.bitfield> y;
+#if __cplusplus <= 201402L
+  // expected-error@-2 {{does not refer to any declaration}} expected-note@-3 {{here}}
+#else
+  // expected-error@-4 {{refers to subobject}}
+#endif
+
+#if __cplusplus >= 201103L
+  const unsigned other = 0;
+  using T = decltype(true ? other : x.bitfield);
+  using T = unsigned;
+#endif
+}
+
diff --git a/clang/test/SemaCXX/constant-expression-cxx11.cpp b/clang/test/SemaCXX/constant-expression-cxx11.cpp
index 8ecf4a48481..a441405939e 100644
--- a/clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -386,6 +386,18 @@ namespace FakeInitList {
   constexpr init_list_2_init_list_3_ints ils = { { { { 1, 2, 3 } }, { { 4, 5, 6 } } } };
 }
 
+namespace ConstAddedByReference {
+  const int &r = (0);
+  constexpr int n = r;
+
+  struct A { constexpr operator int() const { return 0; }};
+  struct B { constexpr operator const int() const { return 0; }};
+  const int &ra = A();
+  const int &rb = B();
+  constexpr int na = ra;
+  constexpr int nb = rb;
+}
+
 }
 
 constexpr int strcmp_ce(const char *p, const char *q) {
diff --git a/clang/test/SemaCXX/constant-expression-cxx1z.cpp b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
index a045234ff9e..1563586e196 100644
--- a/clang/test/SemaCXX/constant-expression-cxx1z.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
@@ -39,3 +39,8 @@ namespace NoexceptFunctionTypes {
   static_assert(A<int>().g());
   static_assert(A<int>()());
 }
+
+namespace Cxx17CD_NB_GB19 {
+  const int &r = 0;
+  constexpr int n = r;
+}
diff --git a/clang/test/SemaCXX/member-init.cpp b/clang/test/SemaCXX/member-init.cpp
index 836c1f7455e..20e4cec5bfd 100644
--- a/clang/test/SemaCXX/member-init.cpp
+++ b/clang/test/SemaCXX/member-init.cpp
@@ -87,7 +87,7 @@ namespace PR14838 {
   struct thing {};
   struct another {
     another() : r(thing()) {}
-    // expected-error@-1 {{temporary of type 'const PR14838::function' has private destructor}}
+    // expected-error@-1 {{temporary of type 'PR14838::function' has private destructor}}
     // expected-warning@-2 {{binding reference member 'r' to a temporary value}}
     const function &r; // expected-note {{reference member declared here}}
   } af;
diff --git a/clang/test/SemaCXX/microsoft-new-delete.cpp b/clang/test/SemaCXX/microsoft-new-delete.cpp
index b929e618a03..beba4d9dd8a 100644
--- a/clang/test/SemaCXX/microsoft-new-delete.cpp
+++ b/clang/test/SemaCXX/microsoft-new-delete.cpp
@@ -16,7 +16,7 @@ void *operator new(size_t, const noncopyable&);
 void *q = new (nc) int[4]; // expected-error {{calling a private constructor}}
 
 struct bitfield { int n : 3; } bf; // expected-note {{here}}
-void *operator new[](size_t, int &);
+void *operator new[](size_t, int &); // expected-note {{passing argument to parameter here}}
 void *operator new(size_t, const int &);
 void *r = new (bf.n) int[4]; // expected-error {{non-const reference cannot bind to bit-field}}
 
diff --git a/clang/test/SemaCXX/reinterpret-cast.cpp b/clang/test/SemaCXX/reinterpret-cast.cpp
index 7c88dc0302a..6cc46d8b0d9 100644
--- a/clang/test/SemaCXX/reinterpret-cast.cpp
+++ b/clang/test/SemaCXX/reinterpret-cast.cpp
@@ -125,7 +125,7 @@ void const_arrays() {
 
 namespace PR9564 {
   struct a { int a : 10; }; a x;
-  int *y = &reinterpret_cast<int&>(x.a); // expected-error {{not allowed}}
+  int *y = &reinterpret_cast<int&>(x.a); // expected-error {{reinterpret_cast from bit-field lvalue to reference type 'int &'}}
 
   __attribute((ext_vector_type(4))) typedef float v4;
   float& w(v4 &a) { return reinterpret_cast<float&>(a[1]); } // expected-error {{not allowed}}