[cfe-commits] r149366 - in /cfe/trunk: include/clang/Basic/DiagnosticASTKinds.td lib/AST/ExprConstant.cpp test/CXX/expr/expr.const/p2-0x.cpp

[Richard Smith]

Author: rsmith
Date: Tue Jan 31 00:41:30 2012
New Revision: 149366

URL: http://llvm.org/viewvc/llvm-project?rev=149366&view=rev
Log:
constexpr: the result of a relational operator between pointers to void is
unspecified unless the pointers are equal; therefore, such a comparison is not
a constant expression unless the pointers are equal.

Modified:
    cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
    cfe/trunk/lib/AST/ExprConstant.cpp
    cfe/trunk/test/CXX/expr/expr.const/p2-0x.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td?rev=149366&r1=149365&r2=149366&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td Tue Jan 31 00:41:30 2012
@@ -53,6 +53,8 @@
 def note_constexpr_typeid_polymorphic : Note<
   "typeid applied to expression of polymorphic type %0 is "
   "not allowed in a constant expression">;
+def note_constexpr_void_comparison : Note<
+  "comparison between unequal pointers to void has unspecified result">;
 def note_constexpr_temporary_here : Note<"temporary created here">;
 def note_constexpr_literal_here : Note<"literal written here">;
 def note_constexpr_depth_limit_exceeded : Note<

Modified: cfe/trunk/lib/AST/ExprConstant.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=149366&r1=149365&r2=149366&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Jan 31 00:41:30 2012
@@ -4331,6 +4331,18 @@
 
       const CharUnits &LHSOffset = LHSValue.getLValueOffset();
       const CharUnits &RHSOffset = RHSValue.getLValueOffset();
+
+      // C++11 [expr.rel]p3:
+      //   Pointers to void (after pointer conversions) can be compared, with a
+      //   result defined as follows: If both pointers represent the same
+      //   address or are both the null pointer value, the result is true if the
+      //   operator is <= or >= and false otherwise; otherwise the result is
+      //   unspecified.
+      // We interpret this as applying to pointers to *cv* void.
+      if (LHSTy->isVoidPointerType() && LHSOffset != RHSOffset &&
+          E->getOpcode() != BO_EQ && E->getOpcode() != BO_NE)
+        CCEDiag(E, diag::note_constexpr_void_comparison);
+
       switch (E->getOpcode()) {
       default: llvm_unreachable("missing comparison operator");
       case BO_LT: return Success(LHSOffset < RHSOffset, E);

Modified: cfe/trunk/test/CXX/expr/expr.const/p2-0x.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/expr/expr.const/p2-0x.cpp?rev=149366&r1=149365&r2=149366&view=diff
==============================================================================
--- cfe/trunk/test/CXX/expr/expr.const/p2-0x.cpp (original)
+++ cfe/trunk/test/CXX/expr/expr.const/p2-0x.cpp Tue Jan 31 00:41:30 2012
@@ -376,10 +376,21 @@
   // If two pointers point to non-static data members of the same object with
   // different access control, the result is unspecified.
 
-  // FIXME:
   // [expr.rel]p3: Pointers to void can be compared [...] if both pointers
   // represent the same address or are both the null pointer [...]; otherwise
   // the result is unspecified.
+  struct S { int a, b; } s;
+  constexpr void *null = 0;
+  constexpr void *pv = (void*)&s.a;
+  constexpr void *qv = (void*)&s.b;
+  constexpr bool v1 = null < 0;
+  constexpr bool v2 = null < pv; // expected-error {{constant expression}}
+  constexpr bool v3 = null == pv; // ok
+  constexpr bool v4 = qv == pv; // ok
+  constexpr bool v5 = qv >= pv; // expected-error {{constant expression}} expected-note {{unequal pointers to void}}
+  constexpr bool v6 = qv > null; // expected-error {{constant expression}}
+  constexpr bool v7 = qv <= (void*)&s.b; // ok
+  constexpr bool v8 = qv > (void*)&s.a; // expected-error {{constant expression}} expected-note {{unequal pointers to void}}
 
   // FIXME: Implement comparisons of pointers to members.
   // [expr.eq]p2: If either is a pointer to a virtual member function and