Implement C++ semantics for C-style and functional-style casts. This regresses Clang extension conversions, like vectors, but allows conversions via constructors and conversion operators.

Add custom conversions to static_cast.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@77076 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -1395,36 +1395,46 @@ def note_property_impl_required : Note<
 
 
 // C++ casts
-def err_bad_cxx_cast_generic : Error<"%0 from %2 to %1 is not allowed">;
-def err_bad_cxx_cast_rvalue : Error<"%0 from rvalue to reference type %1">;
+// These messages adhere to the TryCast pattern: %0 is an int specifying the
+// cast type, %1 is the source type, %2 is the destination type.
+def err_bad_cxx_cast_generic : Error<
+  "%select{const_cast|static_cast|reinterpret_cast|dynamic_cast|C-style cast|"
+  "functional-style cast}0 from %1 to %2 is not allowed">;
+def err_bad_cxx_cast_rvalue : Error<
+  "%select{const_cast|static_cast|reinterpret_cast|dynamic_cast|C-style cast|"
+  "functional-style cast}0 from rvalue to reference type %2">;
 def err_bad_cxx_cast_const_away : Error<
-  "%0 from %2 to %1 casts away constness">;
+  "%select{const_cast|static_cast|reinterpret_cast|dynamic_cast|C-style cast|"
+  "functional-style cast}0 from %1 to %2 casts away constness">;
 def err_bad_const_cast_dest : Error<
-  "const_cast to %0, which is not a reference, pointer-to-object, "
-  "or pointer-to-data-member">;
-
-def err_bad_reinterpret_cast_same_type : Error<
-  "source and destination type of reinterpret_cast are not distinct">;
-def ext_reinterpret_cast_fn_obj : Extension<
-  "reinterpret_cast between pointer-to-function and pointer-to-object is "
-  "an extension">;
-
+  "%select{const_cast||||C-style cast|functional-style cast}0 to %2, "
+  "which is not a reference, pointer-to-object, or pointer-to-data-member">;
+def ext_cast_fn_obj : Extension<
+  "cast between pointer-to-function and pointer-to-object is an extension">;
 def err_bad_reinterpret_cast_small_int : Error<
-  "cast from pointer to smaller type %0 loses information">;
+  "cast from pointer to smaller type %2 loses information">;
+def err_bad_lvalue_to_rvalue_cast : Error<
+  "cannot cast from lvalue of type %1 to rvalue reference type %2; types are "
+  "not compatible">;
+def err_bad_static_cast_pointer_nonpointer : Error<
+  "cannot cast from type %1 to pointer type %2">;
+def err_bad_static_cast_member_pointer_nonmp : Error<
+  "cannot cast from type %1 to member pointer type %2">;
+
+// These messages don't adhere to the pattern.
+// FIXME: Display the path somehow better.
+def err_ambiguous_base_to_derived_cast : Error<
+  "ambiguous cast from base %0 to derived %1:%2">;
+def err_static_downcast_via_virtual : Error<
+  "cannot cast %0 to %1 via virtual base %2">;
+def err_downcast_from_inaccessible_base : Error<
+  "cannot cast %1 to %0 due to inaccessible conversion path">;
 def err_bad_dynamic_cast_not_ref_or_ptr : Error<
   "%0 is not a reference or pointer">;
 def err_bad_dynamic_cast_not_class : Error<"%0 is not a class">;
 def err_bad_dynamic_cast_incomplete : Error<"%0 is an incomplete type">;
 def err_bad_dynamic_cast_not_ptr : Error<"%0 is not a pointer">;
 def err_bad_dynamic_cast_not_polymorphic : Error<"%0 is not polymorphic">;
-// FIXME: Display the path somehow better.
-def err_ambiguous_base_to_derived_cast : Error<
-  "ambiguous static_cast from base %0 to derived %1:%2">;
-def err_static_downcast_via_virtual : Error<
-  "cannot cast %0 to %1 via virtual base %2">;
-def err_bad_lvalue_to_rvalue_cast : Error<
-  "cannot cast from lvalue of type %0 to rvalue reference to %1; types are "
-  "not compatible">;
 
 // Other C++ expressions
 def err_need_header_before_typeid : Error<

lib/Sema/Sema.h

@@ -3169,9 +3169,10 @@ public:
                           bool AllowExplicit = false,
                           bool ForceRValue = false);
 
-  /// CheckCastTypes - Check type constraints for casting between types.
+  /// CheckCastTypes - Check type constraints for casting between types under
+  /// C semantics.
   bool CheckCastTypes(SourceRange TyRange, QualType CastTy, Expr *&CastExpr);
-  
+
   // CheckVectorCast - check type constraints for vectors. 
   // Since vectors are an extension, there are no C standard reference for this.
   // We allow casting between vectors and integer datatypes of the same size.
@@ -3184,7 +3185,11 @@ public:
   // or vectors and the element type of that vector.
   // returns true if the cast is invalid
   bool CheckExtVectorCast(SourceRange R, QualType VectorTy, QualType Ty);
-  
+
+  /// CXXCheckCStyleCast - Check constraints of a C-style or function-style
+  /// cast under C++ semantics.
+  bool CXXCheckCStyleCast(SourceRange R, QualType CastTy, Expr *&CastExpr);
+
   /// CheckMessageArgumentTypes - Check types in an Obj-C message send. 
   /// \param Method - May be null.
   /// \param [out] ReturnType - The return type of the send.
@@ -3196,7 +3201,7 @@ public:
 
   /// CheckCXXBooleanCondition - Returns true if conversion to bool is invalid.
   bool CheckCXXBooleanCondition(Expr *&CondExpr);
-                    
+
   /// ConvertIntegerToTypeWarnOnOverflow - Convert the specified APInt to have
   /// the specified width and sign.  If an overflow occurs, detect it and emit
   /// the specified diagnostic.

lib/Sema/SemaExpr.cpp

@@ -2919,14 +2919,15 @@ Sema::ActOnInitList(SourceLocation LBraceLoc, MultiExprArg initlist,
 
 /// CheckCastTypes - Check type constraints for casting between types.
 bool Sema::CheckCastTypes(SourceRange TyR, QualType castType, Expr *&castExpr) {
+  if (getLangOptions().CPlusPlus)
+    return CXXCheckCStyleCast(TyR, castType, castExpr);
+
   UsualUnaryConversions(castExpr);
 
   // C99 6.5.4p2: the cast type needs to be void or scalar and the expression
   // type needs to be scalar.
   if (castType->isVoidType()) {
     // Cast to void allows any expr type.
-  } else if (castType->isDependentType() || castExpr->isTypeDependent()) {
-    // We can't check any more until template instantiation time.
   } else if (!castType->isScalarType() && !castType->isVectorType()) {
     if (Context.getCanonicalType(castType).getUnqualifiedType() ==
         Context.getCanonicalType(castExpr->getType().getUnqualifiedType()) &&
@@ -3040,7 +3041,8 @@ Sema::ActOnCastExpr(SourceLocation LParenLoc, TypeTy *Ty,
 
   if (CheckCastTypes(SourceRange(LParenLoc, RParenLoc), castType, castExpr))
     return ExprError();
-  return Owned(new (Context) CStyleCastExpr(castType, castExpr, castType,
+  return Owned(new (Context) CStyleCastExpr(castType.getNonReferenceType(),
+                                            castExpr, castType,
                                             LParenLoc, RParenLoc));
 }
 

lib/Sema/SemaOverload.cpp

@@ -1136,7 +1136,7 @@ bool Sema::isObjCPointerConversion(QualType FromType, QualType ToType,
 
 /// CheckPointerConversion - Check the pointer conversion from the
 /// expression From to the type ToType. This routine checks for
-/// ambiguous (FIXME: or inaccessible) derived-to-base pointer
+/// ambiguous or inaccessible derived-to-base pointer
 /// conversions for which IsPointerConversion has already returned
 /// true. It returns true and produces a diagnostic if there was an
 /// error, or returns false otherwise.

test/Parser/cxx-ambig-paren-expr.cpp

@@ -5,9 +5,9 @@ void f() {
   int x, *px;
   
   // Type id.
-  (T())x;    // expected-error {{used type 'T ()'}}
-  (T())+x;   // expected-error {{used type 'T ()'}}
-  (T())*px;  // expected-error {{used type 'T ()'}}
+  (T())x;    // expected-error {{cast from 'int' to 'T ()'}}
+  (T())+x;   // expected-error {{cast from 'int' to 'T ()'}}
+  (T())*px;  // expected-error {{cast from 'int' to 'T ()'}}
   
   // Expression.
   x = (T());

test/SemaCXX/cstyle-cast.cpp

@@ -0,0 +1,231 @@
+// RUN: clang-cc -fsyntax-only -verify -faccess-control %s
+
+struct A {};
+
+// ----------- const_cast --------------
+
+typedef char c;
+typedef c *cp;
+typedef cp *cpp;
+typedef cpp *cppp;
+typedef cppp &cpppr;
+typedef const cppp &cpppcr;
+typedef const char cc;
+typedef cc *ccp;
+typedef volatile ccp ccvp;
+typedef ccvp *ccvpp;
+typedef const volatile ccvpp ccvpcvp;
+typedef ccvpcvp *ccvpcvpp;
+typedef int iar[100];
+typedef iar &iarr;
+typedef int (*f)(int);
+
+void t_cc()
+{
+  ccvpcvpp var = 0;
+  // Cast away deep consts and volatiles.
+  char ***var2 = (cppp)(var);
+  char ***const &var3 = var2;
+  // Const reference to reference.
+  char ***&var4 = (cpppr)(var3);
+  // Drop reference. Intentionally without qualifier change.
+  char *** var5 = (cppp)(var4);
+  const int ar[100] = {0};
+  // Array decay. Intentionally without qualifier change.
+  int *pi = (int*)(ar);
+  f fp = 0;
+  // Don't misidentify fn** as a function pointer.
+  f *fpp = (f*)(&fp);
+  int const A::* const A::*icapcap = 0;
+  int A::* A::* iapap = (int A::* A::*)(icapcap);
+}
+
+// ----------- static_cast -------------
+
+struct B : public A {};             // Single public base.
+struct C1 : public virtual B {};    // Single virtual base.
+struct C2 : public virtual B {};
+struct D : public C1, public C2 {}; // Diamond
+struct E : private A {};            // Single private base.
+struct F : public C1 {};            // Single path to B with virtual.
+struct G1 : public B {};
+struct G2 : public B {};
+struct H : public G1, public G2 {}; // Ambiguous path to B.
+
+enum Enum { En1, En2 };
+enum Onom { On1, On2 };
+
+struct Co1 { operator int(); };
+struct Co2 { Co2(int); };
+struct Co3 { };
+struct Co4 { Co4(Co3); operator Co3(); };
+
+// Explicit implicits
+void t_529_2()
+{
+  int i = 1;
+  (void)(float)(i);
+  double d = 1.0;
+  (void)(float)(d);
+  (void)(int)(d);
+  (void)(char)(i);
+  (void)(unsigned long)(i);
+  (void)(int)(En1);
+  (void)(double)(En1);
+  (void)(int&)(i);
+  (void)(const int&)(i);
+
+  int ar[1];
+  (void)(const int*)(ar);
+  (void)(void (*)())(t_529_2);
+
+  (void)(void*)(0);
+  (void)(void*)((int*)0);
+  (void)(volatile const void*)((const int*)0);
+  (void)(A*)((B*)0);
+  (void)(A&)(*((B*)0));
+  (void)(const B*)((C1*)0);
+  (void)(B&)(*((C1*)0));
+  (void)(A*)((D*)0);
+  (void)(const A&)(*((D*)0));
+  (void)(int B::*)((int A::*)0);
+  (void)(void (B::*)())((void (A::*)())0);
+  (void)(A*)((E*)0); // C-style cast ignores access control
+  (void)(void*)((const int*)0); // const_cast appended
+
+  (void)(int)(Co1());
+  (void)(Co2)(1);
+  (void)(Co3)((Co4)(Co3()));
+
+  // Bad code below
+  //(void)(A*)((H*)0); // {{static_cast from 'struct H *' to 'struct A *' is not allowed}}
+}
+
+// Anything to void
+void t_529_4()
+{
+  (void)(1);
+  (void)(t_529_4);
+}
+
+// Static downcasts
+void t_529_5_8()
+{
+  (void)(B*)((A*)0);
+  (void)(B&)(*((A*)0));
+  (void)(const G1*)((A*)0);
+  (void)(const G1&)(*((A*)0));
+  (void)(B*)((const A*)0); // const_cast appended
+  (void)(B&)(*((const A*)0)); // const_cast appended
+  (void)(E*)((A*)0); // access control ignored
+  (void)(E&)(*((A*)0)); // access control ignored
+
+  // Bad code below
+
+  (void)(C1*)((A*)0); // expected-error {{cannot cast 'struct A *' to 'struct C1 *' via virtual base 'struct B'}}
+  (void)(C1&)(*((A*)0)); // expected-error {{cannot cast 'struct A' to 'struct C1 &' via virtual base 'struct B'}}
+  (void)(D*)((A*)0); // expected-error {{cannot cast 'struct A *' to 'struct D *' via virtual base 'struct B'}}
+  (void)(D&)(*((A*)0)); // expected-error {{cannot cast 'struct A' to 'struct D &' via virtual base 'struct B'}}
+  (void)(H*)((A*)0); // expected-error {{ambiguous cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
+  (void)(H&)(*((A*)0)); // expected-error {{ambiguous cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
+
+  // TODO: Test DR427. This requires user-defined conversions, though.
+}
+
+// Enum conversions
+void t_529_7()
+{
+  (void)(Enum)(1);
+  (void)(Enum)(1.0);
+  (void)(Onom)(En1);
+
+  // Bad code below
+
+  (void)(Enum)((int*)0); // expected-error {{C-style cast from 'int *' to 'enum Enum' is not allowed}}
+}
+
+// Void pointer to object pointer
+void t_529_10()
+{
+  (void)(int*)((void*)0);
+  (void)(const A*)((void*)0);
+  (void)(int*)((const void*)0); // const_cast appended
+}
+
+// Member pointer upcast.
+void t_529_9()
+{
+  (void)(int A::*)((int B::*)0);
+
+  // Bad code below
+  (void)(int A::*)((int H::*)0); // expected-error {{ambiguous conversion from pointer to member of derived class 'struct H'}}
+  (void)(int A::*)((int F::*)0); // expected-error {{conversion from pointer to member of class 'struct F'}}
+}
+
+// -------- reinterpret_cast -----------
+
+enum test { testval = 1 };
+struct structure { int m; };
+typedef void (*fnptr)();
+
+// Test conversion between pointer and integral types, as in p3 and p4.
+void integral_conversion()
+{
+  void *vp = (void*)(testval);
+  long l = (long)(vp);
+  (void)(float*)(l);
+  fnptr fnp = (fnptr)(l);
+  (void)(char)(fnp); // expected-error {{cast from pointer to smaller type 'char' loses information}}
+  (void)(long)(fnp);
+}
+
+void pointer_conversion()
+{
+  int *p1 = 0;
+  float *p2 = (float*)(p1);
+  structure *p3 = (structure*)(p2);
+  typedef int **ppint;
+  ppint *deep = (ppint*)(p3);
+  (void)(fnptr*)(deep);
+}
+
+void constness()
+{
+  int ***const ipppc = 0;
+  int const *icp = (int const*)(ipppc);
+  (void)(int*)(icp); // const_cast appended
+  int const *const **icpcpp = (int const* const**)(ipppc); // const_cast appended
+  int *ip = (int*)(icpcpp);
+  (void)(int const*)(ip);
+  (void)(int const* const* const*)(ipppc);
+}
+
+void fnptrs()
+{
+  typedef int (*fnptr2)(int);
+  fnptr fp = 0;
+  (void)(fnptr2)(fp);
+  void *vp = (void*)(fp);
+  (void)(fnptr)(vp);
+}
+
+void refs()
+{
+  long l = 0;
+  char &c = (char&)(l);
+  // Bad: from rvalue
+  (void)(int&)(&c); // expected-error {{C-style cast from rvalue to reference type 'int &'}}
+}
+
+void memptrs()
+{
+  const int structure::*psi = 0;
+  (void)(const float structure::*)(psi);
+  (void)(int structure::*)(psi); // const_cast appended
+
+  void (structure::*psf)() = 0;
+  (void)(int (structure::*)())(psf);
+
+  (void)(void (structure::*)())(psi); // expected-error {{C-style cast from 'int const struct structure::*' to 'void (struct structure::*)()' is not allowed}}
+  (void)(int structure::*)(psf); // expected-error {{C-style cast from 'void (struct structure::*)()' to 'int struct structure::*' is not allowed}}
+}

test/SemaCXX/dcl_ambig_res.cpp

@@ -50,7 +50,7 @@ void foo5()
 void foo6() 
 { 
   (void)(int(1)); //expression 
-  (void)(int())1; // expected-error{{used type}}
+  (void)(int())1; // expected-error{{to 'int ()'}}
 } 
 
 // [dcl.ambig.res]p7:

test/SemaCXX/decl-expr-ambiguity.cpp

@@ -19,7 +19,7 @@ void f() {
   (int(1)); // expected-warning {{expression result unused}}
 
   // type-id
-  (int())1; // expected-error {{used type 'int ()' where arithmetic or pointer type is required}}
+  (int())1; // expected-error {{C-style cast from 'int' to 'int ()' is not allowed}}
 
   // Declarations.
   int fd(T(a)); // expected-warning {{parentheses were disambiguated as a function declarator}}

test/SemaCXX/static-cast.cpp

@@ -1,11 +1,11 @@
-// RUN: clang-cc -fsyntax-only -verify %s
+// RUN: clang-cc -fsyntax-only -verify -faccess-control %s
 
 struct A {};
 struct B : public A {};             // Single public base.
 struct C1 : public virtual B {};    // Single virtual base.
 struct C2 : public virtual B {};
 struct D : public C1, public C2 {}; // Diamond
-struct E : private A {};            // Single private base.
+struct E : private A {};            // Single private base. expected-note 2 {{'private' inheritance specifier here}}
 struct F : public C1 {};            // Single path to B with virtual.
 struct G1 : public B {};
 struct G2 : public B {};
@@ -14,6 +14,11 @@ struct H : public G1, public G2 {}; // Ambiguous path to B.
 enum Enum { En1, En2 };
 enum Onom { On1, On2 };
 
+struct Co1 { operator int(); };
+struct Co2 { Co2(int); };
+struct Co3 { };
+struct Co4 { Co4(Co3); operator Co3(); };
+
 // Explicit implicits
 void t_529_2()
 {
@@ -45,7 +50,9 @@ void t_529_2()
   (void)static_cast<int B::*>((int A::*)0);
   (void)static_cast<void (B::*)()>((void (A::*)())0);
 
-  // TODO: User-defined conversions
+  (void)static_cast<int>(Co1());
+  (void)static_cast<Co2>(1);
+  (void)static_cast<Co3>(static_cast<Co4>(Co3()));
 
   // Bad code below
 
@@ -80,11 +87,10 @@ void t_529_5_8()
   (void)static_cast<D&>(*((A*)0)); // expected-error {{cannot cast 'struct A' to 'struct D &' via virtual base 'struct B'}}
   (void)static_cast<B*>((const A*)0); // expected-error {{static_cast from 'struct A const *' to 'struct B *' casts away constness}}
   (void)static_cast<B&>(*((const A*)0)); // expected-error {{static_cast from 'struct A const' to 'struct B &' casts away constness}}
-  // Accessibility is not yet tested
-  //(void)static_cast<E*>((A*)0); // {{static_cast from 'struct A *' to 'struct E *' is not allowed}}
-  //(void)static_cast<E&>(*((A*)0)); // {{static_cast from 'struct A' to 'struct E &' is not allowed}}
-  (void)static_cast<H*>((A*)0); // expected-error {{ambiguous static_cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
-  (void)static_cast<H&>(*((A*)0)); // expected-error {{ambiguous static_cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
+  (void)static_cast<E*>((A*)0); // expected-error {{cannot cast 'struct A' to 'struct E' due to inaccessible}}
+  (void)static_cast<E&>(*((A*)0)); // expected-error {{cannot cast 'struct A' to 'struct E' due to inaccessible}}
+  (void)static_cast<H*>((A*)0); // expected-error {{ambiguous cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
+  (void)static_cast<H&>(*((A*)0)); // expected-error {{ambiguous cast from base 'struct A' to derived 'struct H':\n    struct A -> struct B -> struct G1 -> struct H\n    struct A -> struct B -> struct G2 -> struct H}}
   (void)static_cast<E*>((B*)0); // expected-error {{static_cast from 'struct B *' to 'struct E *' is not allowed}}
   (void)static_cast<E&>(*((B*)0)); // expected-error {{non-const lvalue reference to type 'struct E' cannot be initialized with a value of type 'struct B'}}
 

test/SemaTemplate/instantiate-cast.cpp

@@ -1,6 +1,6 @@
 // RUN: clang-cc -fsyntax-only -verify %s
 
-struct A { int x; };
+struct A { int x; }; // expected-note 2 {{candidate}}
 
 class Base { 
 public:
@@ -23,7 +23,7 @@ struct Constructible {
 template<typename T, typename U>
 struct CStyleCast0 {
   void f(T t) {
-    (void)((U)t); // FIXME:ugly expected-error{{operand}}
+    (void)((U)t); // expected-error{{C-style cast from 'struct A' to 'int'}}
   }
 };
 
@@ -36,7 +36,7 @@ template struct CStyleCast0<A, int>; // expected-note{{instantiation}}
 template<typename T, typename U>
 struct StaticCast0 {
   void f(T t) {
-    (void)static_cast<U>(t); // expected-error{{static_cast}}
+    (void)static_cast<U>(t); // expected-error{{initialization of 'struct A'}}
   }
 };
 
@@ -89,7 +89,7 @@ template struct ConstCast0<int const *, float *>; // expected-note{{instantiatio
 template<typename T, typename U>
 struct FunctionalCast1 {
   void f(T t) {
-    (void)U(t); // FIXME:ugly expected-error{{operand}}
+    (void)U(t); // expected-error{{C-style cast from 'struct A' to 'int'}}
   }
 };
 

www/cxx_status.html

@@ -540,10 +540,10 @@ welcome!</p>
 <tr>
   <td>&nbsp;&nbsp;&nbsp;&nbsp;5.2.3 [expr.type.conv]</td>
   <td class="complete" align="center"></td>
-  <td class="complete" align="center"></td>
-  <td class="basic"></td>
+  <td class="medium" align="center"></td>
+  <td class="advanced"></td>
   <td></td>
-  <td>Only between non-class types</td>
+  <td>Allows some invalid pointer conversions, AST has little information</td>
 </tr>
 <tr>
   <td>&nbsp;&nbsp;&nbsp;&nbsp;5.2.4 [expr.pseudo]</td>
@@ -588,10 +588,10 @@ welcome!</p>
 <tr>
   <td>&nbsp;&nbsp;&nbsp;&nbsp;5.2.9 [expr.static.cast]</td>
   <td class="complete" align="center"></td>
-  <td class="complete" align="center"></td>
+  <td class="medium" align="center"></td>
   <td class="advanced" align="center"></td>
   <td></td>
-  <td>Some custom conversions don't work.</td>
+  <td>Allows some invalid pointer conversions, AST has little information</td>
 </tr>
 <tr>
   <td>&nbsp;&nbsp;&nbsp;&nbsp;5.2.10 [expr.reinterpret.cast]</td>
@@ -694,10 +694,10 @@ welcome!</p>
 <tr>
   <td>&nbsp;&nbsp;5.4 [expr.cast]</td>
   <td class="complete" align="center"></td>
-  <td class="complete" align="center"></td>
-  <td class="medium"></td>
+  <td class="medium" align="center"></td>
+  <td class="advanced"></td>
   <td></td>
-  <td>Too lenient, and may not always have correct semantics</td>
+  <td>Allows some invalid pointer conversions, AST has little information</td>
 </tr>
 <tr>
   <td>&nbsp;&nbsp;5.5 [expr.mptr.oper]</td>