[Bug c/32643] New: Wrong error message with unsigned char a = uchar&512

[Bug c/32643] New: Wrong error message with unsigned char a = uchar&512

[pinskia at gcc dot gnu dot org]

testcase, compile with -pedantic-errors (we don't reject it overwise in 4.3):
unsigned char p;
unsigned char p1 = p & 512;
------------- cut -------
We get:
overflow-warn-5.c:7: warning: overflow in implicit constant conversion
overflow-warn-5.c:7: error: overflow in constant expression

Now there is an overflow but only because we optimize the IR (unsigned
char)(((int)p)& 512) into:
p & (unsigned char)512 and (unsigned char)512 is converted into 0 (with
overflow) so we have p & 0 which is then optimized into 0(with overflow).  So
we are only rejecting this because of the overflow due to the conversion (which
was due to fold).


We don't reject as invalid code either:
unsigned char p;
unsigned char p1 = p & 0;


-- 
           Summary: Wrong error message with unsigned char a = uchar&512
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid, diagnostic
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-07-06 09:07 -------
Note this was found while trying to fix PR 32628.

The diagnostic issue is at least a regression from 4.0.1.  Well and the accepts
invalid (without -pedantic-errors for the first testcase).

The second testcase was  accepted wrongly in 4.0.1 also.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.3.0
      Known to work|                            |4.0.1
            Summary|Wrong error message with    |[4.3 Regression] Wrong error
                   |unsigned char a = uchar&512 |message with unsigned char a
                   |                            |= uchar&512


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-07-06 09:43 -------
This quick hack fixes the problem for both testcases (the fold-const part is
the only part required to fix the second testcase);
Index: fold-const.c
===================================================================
--- fold-const.c        (revision 126396)
+++ fold-const.c        (working copy)
@@ -3278,7 +3278,7 @@
 {
   tree t = fold_convert (type, result);

-  if (TREE_SIDE_EFFECTS (omitted))
+  if (folding_initializer || TREE_SIDE_EFFECTS (omitted))
     return build2 (COMPOUND_EXPR, type, fold_ignored_result (omitted), t);

   return non_lvalue (t);
@@ -3291,7 +3291,7 @@
 {
   tree t = fold_convert (type, result);

-  if (TREE_SIDE_EFFECTS (omitted))
+  if (folding_initializer || TREE_SIDE_EFFECTS (omitted))
     return build2 (COMPOUND_EXPR, type, fold_ignored_result (omitted), t);

   return pedantic_non_lvalue (t);
@@ -14438,6 +14438,10 @@
 tree
 fold_ignored_result (tree t)
 {
+  /* Just for now, if this is an initializer.   */
+  if (folding_initializer)
+    return t;
+
   if (!TREE_SIDE_EFFECTS (t))
     return integer_zero_node;

Index: c-typeck.c
===================================================================
--- c-typeck.c  (revision 126396)
+++ c-typeck.c  (working copy)
@@ -3783,7 +3783,8 @@
   enum tree_code coder;
   tree rname = NULL_TREE;
   bool objc_ok = false;
-
+  int old_folding_initializer;
+  
   if (errtype == ic_argpass || errtype == ic_argpass_nonproto)
     {
       tree selector;
@@ -3918,13 +3919,29 @@
           && (coder == INTEGER_TYPE || coder == REAL_TYPE
               || coder == ENUMERAL_TYPE || coder == COMPLEX_TYPE
               || coder == BOOLEAN_TYPE))
-    return convert_and_check (type, rhs);
+    {
+      tree new;
+      old_folding_initializer = folding_initializer;
+      if (errtype == ic_init)
+       folding_initializer = 1;
+      new = convert_and_check (type, rhs);
+      folding_initializer = old_folding_initializer;
+      return new;
+    }

   /* Aggregates in different TUs might need conversion.  */
   if ((codel == RECORD_TYPE || codel == UNION_TYPE)
       && codel == coder
       && comptypes (type, rhstype))
-    return convert_and_check (type, rhs);
+    {
+      tree new;
+      old_folding_initializer = folding_initializer;
+      if (errtype == ic_init)
+       folding_initializer = 1;
+      new = convert_and_check (type, rhs);
+      folding_initializer = old_folding_initializer;
+      return new;
+    }

   /* Conversion to a transparent union from its member types.
      This applies only to function arguments.  */


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2007-07-08 10:12 -------
(In reply to comment #0)
> testcase, compile with -pedantic-errors (we don't reject it overwise in 4.3):
> unsigned char p;
> unsigned char p1 = p & 512;
> 
> Now there is an overflow but only because we optimize the IR (unsigned
> char)(((int)p)& 512) into:
> p & (unsigned char)512 and (unsigned char)512 is converted into 0 (with
> overflow) so we have p & 0 which is then optimized into 0(with overflow).  So
> we are only rejecting this because of the overflow due to the conversion (which
> was due to fold).

There should not be any overflow? So the result is wrong independently whether
this is an initialization or not? The operation should be done with int, isn't
it?  

BTW, you should get two warnings when using -pedantic.

> We don't reject as invalid code either:
> unsigned char p;
> unsigned char p1 = p & 0;

Why should we? There is no overflow here, you mean that p is not constant? I
think we have two issues in the first testcase, one is folding (X op 0), the
other is converting 512 to uchar before performing the operation. Am I wrong?


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-07-08 10:19 -------
(In reply to comment #3)
> > We don't reject as invalid code either:
> > unsigned char p;
> > unsigned char p1 = p & 0;
> 
> Why should we? There is no overflow here, you mean that p is not constant? I
> think we have two issues in the first testcase, one is folding (X op 0), the
> other is converting 512 to uchar before performing the operation. Am I wrong?

Yes, the converting 512 to uchar is a valid optimization.  That is:
(char)(((int) a) & b)
is the same as:
a & ((char)b)
if a is of type char.
as there are no overflow concerns with AND.

The folding gets us to the case where we have "a & 0" which is not a valid
constant initializer at all.

Note I found this while working on fixing PR 32628, where the patch which fixes
that caues us to no longer emit a warning/error for the first testcase.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |32628
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-12-07 20:19 -------
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-12-07 20:19:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-03-14 16:52 -------
Adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.0                       |4.3.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2008-06-06 14:57 -------
4.3.1 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.1                       |4.3.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[jsm28 at gcc dot gnu dot org]

------- Comment #8 from jsm28 at gcc dot gnu dot org  2008-08-27 22:02 -------
4.3.2 is released, changing milestones to 4.3.3.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.2                       |4.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[manu at gcc dot gnu dot org]

------- Comment #9 from manu at gcc dot gnu dot org  2008-11-03 10:40 -------
Andrew,

what is the status of this? 

Joseph, 

Will this be fixed by your new code for 4.5?


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jsm28 at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[joseph at codesourcery dot com]

------- Comment #10 from joseph at codesourcery dot com  2008-11-03 12:58 -------
Subject: Re:  [4.2/4.3/4.4 Regression] Wrong error message with
 unsigned char a = uchar&512

On Mon, 3 Nov 2008, manu at gcc dot gnu dot org wrote:

> Joseph, 
> 
> Will this be fixed by your new code for 4.5?

As I said in <http://gcc.gnu.org/ml/gcc-patches/2008-10/msg01061.html>, 
that patch does not fix this bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2009-01-24 10:19 -------
GCC 4.3.3 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.3                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.2/4.3/4.4/4.5 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2009-08-04 12:28 -------
GCC 4.3.4 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643

[Bug c/32643] [4.3/4.4/4.5/4.6 Regression] Wrong error message with unsigned char a = uchar&512

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2010-05-22 18:11 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32643