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Re: missed uninitialised variable warning

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


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

RCS file: /cvs/gcc/gcc/gcc/,v
retrieving revision 1.1135
diff -u -p -r1.1135
--- 1 Aug 2003 14:04:00 -0000 1.1135
+++ 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"

@@ -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 || 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);

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