re PR middle-end/44100 (ICE compiling g++.dg/init/struct2.C on Tru64 UNIX V5.1B)

	PR middle-end/44100
	* typeck.c (cp_build_unary_op): Fold offsetof-like computations.

From-SVN: r159800

gcc/cp/ChangeLog

+2010-05-24  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR middle-end/44100
+	* typeck.c (cp_build_unary_op): Fold offsetof-like computations.
+
 2010-05-24  Joseph Myers  <joseph@codesourcery.com>
 
 	* error.c (cp_diagnostic_starter): Update call to

gcc/cp/typeck.c

@@ -5024,6 +5024,20 @@ cp_build_unary_op (enum tree_code code, tree xarg, int noconvert,
 	  return arg;
 	}
 
+      /* ??? Cope with user tricks that amount to offsetof.  */
+      if (TREE_CODE (argtype) != FUNCTION_TYPE
+	  && TREE_CODE (argtype) != METHOD_TYPE
+	  && argtype != unknown_type_node
+	  && (val = get_base_address (arg))
+	  && TREE_CODE (val) == INDIRECT_REF
+	  && TREE_CONSTANT (TREE_OPERAND (val, 0)))
+	{
+	  tree type = build_pointer_type (argtype);
+	  tree op0 = fold_convert (type, TREE_OPERAND (val, 0));
+	  tree op1 = fold_convert (sizetype, fold_offsetof (arg, val));
+	  return fold_build2 (POINTER_PLUS_EXPR, type, op0, op1);
+	}
+
       /* Uninstantiated types are all functions.  Taking the
 	 address of a function is a no-op, so just return the
 	 argument.  */

gcc/testsuite/ChangeLog

 2010-05-24  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* g++.dg/parse/array-size2.C: Remove dg-error directives.
+
+2010-05-24  Eric Botcazou  <ebotcazou@adacore.com>
+
 	PR ada/38394
 	* gnat.dg/array13.ad[sb]: New test.
 

gcc/testsuite/g++.dg/parse/array-size2.C

 // PR c/25682
 // { dg-do compile }
-// Test whether we don't ICE on invalid array sizes.
+// Test whether we don't ICE on questionable constructs where offsetof
+// should have been used instead.
 
 struct S
 {
@@ -13,7 +14,7 @@ extern void bar (char *, char *);
 void
 foo (void)
 {
-  char g[(char *) &((struct S *) 0)->b - (char *) 0];	// { dg-error "not an integral constant-expression" }
-  char h[(__SIZE_TYPE__) &((struct S *) 8)->b];		// { dg-error "not an integral constant-expression" }
+  char g[(char *) &((struct S *) 0)->b - (char *) 0];
+  char h[(__SIZE_TYPE__) &((struct S *) 8)->b];
   bar (g, h);
 }