Re: missed uninitialised variable warning

[Andrew Pinski <pinskia at physics dot uc dot edu>]

On Monday, Aug 4, 2003, at 09:20 US/Eastern, Michael Matz wrote:

> Hi,
>
> On 4 Aug 2003, Gabriel Dos Reis wrote:
>
> > | Hmm, hard to fix ...  I don't know, the patch below does it for the 
> > easy
> > | 'x = x' case.  But I immediately withdraw it, as I like this 
> > feature ;-)
> >
> > where were you when people argued with that? ;-)
>
> I think I also argued for this feature.  ;-)
>
> The patch catches only one certain instance of the whole recursive
> initialization problem.  Namely it does not catch things like
> "int i = g(i); int j = j + 1;" , i.e. any more complicated expression 
> than
> the var itself.


Here is a patch which should warn about more complicated expressions.
If you want to limit gcc not warn about int i=i;, then add a condition 
in contains_exp
for the case x==t and change the name of contains_exp.


Thanks,
Andrew Pinski

Index: Makefile.in
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Makefile.in,v
retrieving revision 1.1135
diff -u -p -r1.1135 Makefile.in
--- Makefile.in	1 Aug 2003 14:04:00 -0000	1.1135
+++ Makefile.in	4 Aug 2003 13:54:13 -0000
@@ -1525,7 +1525,7 @@ varasm.o : varasm.c $(CONFIG_H) $(SYSTEM
 function.o : function.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) 
$(RTL_H) $(TREE_H) \
    flags.h function.h $(EXPR_H) $(OPTABS_H) libfuncs.h $(REGS_H) 
hard-reg-set.h \
    insn-config.h $(RECOG_H) output.h toplev.h except.h $(HASHTAB_H) 
$(GGC_H) \
-   $(TM_P_H) langhooks.h gt-function.h
+   $(TM_P_H) tree-inline.h langhooks.h gt-function.h
 stmt.o : stmt.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_H) 
$(TREE_H) flags.h \
    function.h insn-config.h hard-reg-set.h $(EXPR_H) libfuncs.h 
except.h \
    $(LOOP_H) $(RECOG_H) toplev.h output.h varray.h $(GGC_H) $(TM_P_H) \
Index: function.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/function.c,v
retrieving revision 1.449
diff -u -p -r1.449 function.c
--- function.c	25 Jul 2003 09:52:25 -0000	1.449
+++ function.c	4 Aug 2003 13:54:13 -0000
@@ -62,6 +62,7 @@ Software Foundation, 59 Temple Place - S
 #include "tm_p.h"
 #include "integrate.h"
 #include "langhooks.h"
+#include "tree-inline.h"

 #ifndef TRAMPOLINE_ALIGNMENT
 #define TRAMPOLINE_ALIGNMENT FUNCTION_BOUNDARY
@@ -5539,6 +5540,24 @@ pad_below (struct args_size *offset_ptr,
     }
 }
 
+/* Is the tree, t, the expression x. */
+static tree
+contains_exp_1 (tree *t , int *walk_sub_trees, void *x)
+{
+  if (*t == x)
+    return t;
+  return NULL_TREE;
+}
+
+/* Does the tree, t, contain the expression x. */
+static bool
+contains_exp (tree t, tree x)
+{
+  if (walk_tree_without_duplicates ( &t, contains_exp_1, x))
+    return true;
+  return false;
+}
+
 /* Walk the tree of blocks describing the binding levels within a 
function
    and warn about uninitialized variables.
    This is done after calling flow_analysis and before global_alloc
@@ -5566,7 +5585,8 @@ uninitialized_vars_warning (tree block)

 	     We do not care about the actual value in DECL_INITIAL, so we do
 	     not worry that it may be a dangling pointer.  */
-	  && DECL_INITIAL (decl) == NULL_TREE
+	  && (DECL_INITIAL (decl) == NULL_TREE || contains_exp (DECL_INITIAL 
(decl), decl) )
 	  && regno_uninitialized (REGNO (DECL_RTL (decl))))
 	warning ("%H'%D' might be used uninitialized in this function",
                  &DECL_SOURCE_LOCATION (decl), decl);