varasm.c (initializer_constant_valid_p): Indicate subtraction of pointers to the…

varasm.c (initializer_constant_valid_p): Indicate subtraction of pointers to the same string constant is absolute.

2000-12-28  Jeffrey Oldham  <oldham@codesourcery.com>

	* varasm.c (initializer_constant_valid_p): Indicate subtraction of
	pointers to the same string constant is absolute.

From-SVN: r38514

gcc/ChangeLog

+2000-12-28  Jeffrey Oldham  <oldham@codesourcery.com>
+
+	* varasm.c (initializer_constant_valid_p): Indicate subtraction of
+	pointers to the same string constant is absolute.
+
 2000-12-28  Joseph S. Myers  <jsm28@cam.ac.uk>
 
 	* c-common.c (enum format_type): Add strfmon_format_type.

gcc/varasm.c

@@ -4252,6 +4252,14 @@ initializer_constant_valid_p (value, endtype)
 	     Then the value is absolute.  */
 	  if (valid0 == valid1 && valid0 != 0)
 	    return null_pointer_node;
+
+	  /* Since GCC guarantees that string constants are unique in the
+	     generated code, a subtraction between two copies of the same
+	     constant string is absolute.  */
+	  if (valid0 && TREE_CODE (valid0) == STRING_CST &&
+	      valid1 && TREE_CODE (valid1) == STRING_CST &&
+	      TREE_STRING_POINTER (valid0) == TREE_STRING_POINTER (valid1))
+	    return null_pointer_node;
 	}
 
       /* Support differences between labels.  */