vec.h (VEC_BASE): If base is at offset 0 in the structure, use &(P)->base even if P is NULL.

	* vec.h (VEC_BASE): If base is at offset 0 in the structure,
	use &(P)->base even if P is NULL.

From-SVN: r181258

gcc/ChangeLog

 2011-11-10  Jakub Jelinek  <jakub@redhat.com>
 
+	* vec.h (VEC_BASE): If base is at offset 0 in the structure,
+	use &(P)->base even if P is NULL.
+
 	PR rtl-optimization/51023
 	* combine.c (simplify_comparison) <case SIGN_EXTEND>: Don't use
 	val_signbit_known_clear_p for signed comparison narrowing

gcc/vec.h

@@ -549,7 +549,12 @@ typedef struct VEC(T,A)							  \
 } VEC(T,A)
 
 /* Convert to base type.  */
+#if GCC_VERSION >= 4000
+#define VEC_BASE(P) \
+  ((offsetof (__typeof (*P), base) == 0 || (P)) ? &(P)->base : 0)
+#else
 #define VEC_BASE(P)  ((P) ? &(P)->base : 0)
+#endif
 
 /* Vector of integer-like object.  */
 #define DEF_VEC_I(T)							  \