(c_expand_return): Refine check for returning pointer to local

variable to allow subtracting a pointer from it.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@8837 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index b295be7..ceabea8 100644 (file)
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -1,5 +1,5 @@
 /* Build expressions with type checking for C compiler.
-   Copyright (C) 1987, 88, 91, 92, 93, 1994 Free Software Foundation, Inc.
+   Copyright (C) 1987, 88, 91, 92, 93, 94, 1995 Free Software Foundation, Inc.
 
 This file is part of GNU CC.
 
@@ -6348,25 +6348,50 @@ c_expand_return (retval)
 
       /* Strip any conversions, additions, and subtractions, and see if
         we are returning the address of a local variable.  Warn if so.  */
-      while (TREE_CODE (inner) == NOP_EXPR
-            || TREE_CODE (inner) == NON_LVALUE_EXPR
-            || TREE_CODE (inner) == CONVERT_EXPR
-            || TREE_CODE (inner) == PLUS_EXPR
-            || TREE_CODE (inner) == MINUS_EXPR)
-       inner = TREE_OPERAND (inner, 0);
-
-      if (TREE_CODE (inner) == ADDR_EXPR)
+      while (1)
        {
-         inner = TREE_OPERAND (inner, 0);
+         switch (TREE_CODE (inner))
+           {
+           case NOP_EXPR:   case NON_LVALUE_EXPR:  case CONVERT_EXPR:
+           case PLUS_EXPR:
+             inner = TREE_OPERAND (inner, 0);
+             continue;
+
+           case MINUS_EXPR:
+             /* If the second operand of the MINUS_EXPR has a pointer
+                type (or is converted from it), this may be valid, so
+                don't give a warning.  */
+             {
+               tree op1 = TREE_OPERAND (inner, 1);
+
+               while (! POINTER_TYPE_P (TREE_TYPE (op1))
+                      && (TREE_CODE (op1) == NOP_EXPR
+                          || TREE_CODE (op1) == NON_LVALUE_EXPR
+                          || TREE_CODE (op1) == CONVERT_EXPR))
+                 op1 = TREE_OPERAND (op1, 0);
+
+               if (POINTER_TYPE_P (TREE_TYPE (op1)))
+                 break;
 
-         while (TREE_CODE_CLASS (TREE_CODE (inner)) == 'r')
-           inner = TREE_OPERAND (inner, 0);
+               inner = TREE_OPERAND (inner, 0);
+               continue;
+             }
+             
+           case ADDR_EXPR:
+             inner = TREE_OPERAND (inner, 0);
 
-         if (TREE_CODE (inner) == VAR_DECL
-             && ! DECL_EXTERNAL (inner)
-             && ! TREE_STATIC (inner)
-             && DECL_CONTEXT (inner) == current_function_decl)
-           warning ("function returns address of local variable");
+             while (TREE_CODE_CLASS (TREE_CODE (inner)) == 'r')
+               inner = TREE_OPERAND (inner, 0);
+
+             if (TREE_CODE (inner) == VAR_DECL
+                 && ! DECL_EXTERNAL (inner)
+                 && ! TREE_STATIC (inner)
+                 && DECL_CONTEXT (inner) == current_function_decl)
+               warning ("function returns address of local variable");
+             break;
+           }
+
+         break;
        }
 
       t = build (MODIFY_EXPR, TREE_TYPE (res), res, t);