C++ PATCH for c++/85277, ICE with invalid offsetof

[Jason Merrill <jason at redhat dot com>]

Here, the code was improperly assuming that the member argument must
be a decl at the point of the error, but since we stopped folding
foo[0] to foo, in this case it's an INDIRECT_REF.

And the existing error for INDIRECT_REF is inaccurate for this case,
so let's stick to complaining about asking for offsetof a function.

While I was here, I updated the non-standard-layout diagnostic to say
"conditionally-supported" rather than undefined.

Tested x86_64-cp-linux-gnu, applying to trunk.

commit cb3221a892dc8ea6c06d148b3756d82067644869
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Apr 9 12:51:38 2018 -0400

            PR c++/85277 - ICE with invalid offsetof.
    
            * semantics.c (finish_offsetof): Avoid passing non-DECL to %qD.
            Adjust -Winvalid-offsetof diagnostic to say conditionally supported.

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 59cac77f6b7..8c893ed64b0 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -4043,17 +4043,17 @@ finish_offsetof (tree object_ptr, tree expr, location_t loc)
       || TREE_CODE (TREE_TYPE (expr)) == METHOD_TYPE
       || TREE_TYPE (expr) == unknown_type_node)
     {
-      if (INDIRECT_REF_P (expr))
-	error ("second operand of %<offsetof%> is neither a single "
-	       "identifier nor a sequence of member accesses and "
-	       "array references");
-      else
+      while (TREE_CODE (expr) == COMPONENT_REF
+	     || TREE_CODE (expr) == COMPOUND_EXPR)
+	expr = TREE_OPERAND (expr, 1);
+
+      if (DECL_P (expr))
 	{
-	  if (TREE_CODE (expr) == COMPONENT_REF
-	      || TREE_CODE (expr) == COMPOUND_EXPR)
-	    expr = TREE_OPERAND (expr, 1);
 	  error ("cannot apply %<offsetof%> to member function %qD", expr);
+	  inform (DECL_SOURCE_LOCATION (expr), "declared here");
 	}
+      else
+	error ("cannot apply %<offsetof%> to member function");
       return error_mark_node;
     }
   if (TREE_CODE (expr) == CONST_DECL)
@@ -4069,9 +4069,9 @@ finish_offsetof (tree object_ptr, tree expr, location_t loc)
       && CLASS_TYPE_P (TREE_TYPE (TREE_TYPE (object_ptr)))
       && CLASSTYPE_NON_STD_LAYOUT (TREE_TYPE (TREE_TYPE (object_ptr)))
       && cp_unevaluated_operand == 0)
-    pedwarn (loc, OPT_Winvalid_offsetof,
-	     "offsetof within non-standard-layout type %qT is undefined",
-	     TREE_TYPE (TREE_TYPE (object_ptr)));
+    warning_at (loc, OPT_Winvalid_offsetof, "offsetof within "
+		"non-standard-layout type %qT is conditionally-supported",
+		TREE_TYPE (TREE_TYPE (object_ptr)));
   return fold_offsetof (expr);
 }
 
diff --git a/gcc/testsuite/g++.dg/ext/builtin-offsetof1.C b/gcc/testsuite/g++.dg/ext/builtin-offsetof1.C
index 5c5e9cf246b..cbc2daafbdd 100644
--- a/gcc/testsuite/g++.dg/ext/builtin-offsetof1.C
+++ b/gcc/testsuite/g++.dg/ext/builtin-offsetof1.C
@@ -1,9 +1,11 @@
 // PR c++/51413
-// { dg-options "-w" }
+// PR c++/85277
+// { dg-options "-Wno-pointer-arith" }
 
 struct A
 {
   static void foo();
 };
 
-int i = __builtin_offsetof(A, foo[1]);  // { dg-error "neither a single identifier nor a sequence of member accesses and array references" }
+int i = __builtin_offsetof(A, foo[1]);  // { dg-error "offsetof" }
+int j = __builtin_offsetof(volatile A, foo[0]);  // { dg-error "offsetof" }
diff --git a/gcc/testsuite/g++.dg/other/offsetof3.C b/gcc/testsuite/g++.dg/other/offsetof3.C
index 8d982426560..779fc72670a 100644
--- a/gcc/testsuite/g++.dg/other/offsetof3.C
+++ b/gcc/testsuite/g++.dg/other/offsetof3.C
@@ -12,4 +12,4 @@ protected:
 typedef X* pX;
 typedef __SIZE_TYPE__ size_t;
 
-size_t yoff = __builtin_offsetof (X, y); /* { dg-error "35:non-standard-layout" } */
+size_t yoff = __builtin_offsetof (X, y); /* { dg-message "35:non-standard-layout" } */
diff --git a/gcc/testsuite/g++.dg/other/offsetof5.C b/gcc/testsuite/g++.dg/other/offsetof5.C
index 86b14488246..8514af087ad 100644
--- a/gcc/testsuite/g++.dg/other/offsetof5.C
+++ b/gcc/testsuite/g++.dg/other/offsetof5.C
@@ -9,14 +9,14 @@ struct A
   int &i;
 };
 
-int j = offsetof (A, i);		// { dg-error "offsetof" }
+int j = offsetof (A, i);		// { dg-message "offsetof" }
 
 template <typename T>
 struct S
 {
   T h;
   T &i;
-  static const int j = offsetof (S, i);	// { dg-error "offsetof" }
+  static const int j = offsetof (S, i);	// { dg-message "offsetof" }
 };
 
 int k = S<int>::j;			// { dg-message "required from here" }
diff --git a/gcc/testsuite/g++.dg/other/offsetof8.C b/gcc/testsuite/g++.dg/other/offsetof8.C
index 0668199b366..211c5127026 100644
--- a/gcc/testsuite/g++.dg/other/offsetof8.C
+++ b/gcc/testsuite/g++.dg/other/offsetof8.C
@@ -9,4 +9,4 @@ struct B: virtual A { };
 int a[]  = {
   !&((B*)0)->i,    // { dg-error "invalid access to non-static data member" }
   __builtin_offsetof (B, i)   // { dg-error "invalid access to non-static" }
-};			      // { dg-error "offsetof within non-standard-layout type" "" { target *-*-* } .-1 }
+};			      // { dg-message "offsetof within non-standard-layout type" "" { target *-*-* } .-1 }