Full Text Bug Listing

Description:

Last confirmed:

Opened: 2002-10-14 07:36

When evaluating expressions like (unsigned)((int)x/2)/2,
gcc incorrectly merges these two divisions into one signed
(or unsigned in 2.7.2.3) division by 4, producing incorrect
result.

Release:
gcc-2.7.2.3, gcc-2.95.4, gcc-3.0.4, gcc-3.2

Environment:
Bug present in almost all gcc releases, tested on Linux and OS/2.

How-To-Repeat:
Compile and run the file. The bug can be seen with or
without optimizations.

------- Comment #1 From Wolfgang Bangerth 2003-02-02 23:15 -------

State-Changed-From-To: open->analyzed
State-Changed-Why: Same behavior still present with 3.4. Indeed strange.

------- Comment #2 From glen@imodulo.com 2003-03-15 21:50 -------

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org,
	mikulas@artax.karlin.mff.cuni.cz
Cc:  
Subject: Re: c/8224: Incorrect joining of signed and unsigned division
Date: Sat, 15 Mar 2003 21:50:10 +0000

 I'm testing the following patch as a fix to PR c/8224:
 
 	* fold-const.c (extract_muldiv_1): Don't pass through type conversions
 	when signedness changes for division or modulus.
 
 diff -Nru3p gcc-3.3.orig/gcc/fold-const.c gcc-3.3/gcc/fold-const.c
 --- gcc-3.3.orig/gcc/fold-const.c	2003-02-16 08:25:20.000000000 +0000
 +++ gcc-3.3/gcc/fold-const.c	2003-02-16 08:25:20.000000000 +0000
 @@ -4117,7 +4117,12 @@ extract_muldiv_1 (t, c, code, wide_type)
  	      /* ... or its type is larger than ctype,
  		 then we cannot pass through this truncation.  */
  	      || (GET_MODE_SIZE (TYPE_MODE (ctype))
 -		  < GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (op0))))))
 +		  < GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (op0))))
 +	      /* ... or signedness changes for division or modulus,
 +		 then we cannot pass through this conversion.  */
 +	      || (code != MULT_EXPR
 +		  && (TREE_UNSIGNED (ctype)
 +		      != TREE_UNSIGNED (TREE_TYPE (op0))))))
  	break;
  
        /* Pass the constant down and see if we can make a simplification.  If

------- Comment #3 From glen@imodulo.com 2003-03-21 22:48 -------

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Cc:  
Subject: Re: c/8224: Incorrect joining of signed and unsigned division
Date: Fri, 21 Mar 2003 22:48:01 -1000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8224
 
 I'll need someone with CVS write access to commit the following patch:
 http://gcc.gnu.org/ml/gcc-bugs/2003-03/msg00949.html
 Approval is here:
 http://gcc.gnu.org/ml/gcc-patches/2003-03/msg01966.html
 
 FYI, the patch I submitted to gcc-patches is equivalent to the one above
 except I mistakenly forgot the "or modulus" part of the comment.
 Hence, I think the patch sent to gcc-bugs should be committed.
 
 Thanks!
 
 -glen

------- Comment #4 From glen@imodulo.com 2003-03-23 18:33 -------

From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Cc:  
Subject: Re: c/8224: Incorrect joining of signed and unsigned division
Date: Sun, 23 Mar 2003 18:33:20 +0000

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8224
 
 Adding link to test case:
 http://gcc.gnu.org/ml/gcc-patches/2003-03/txt00029.txt

From: mmitchel@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: c/8224 Date: 23 Mar 2003 22:55:51 -0000 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_3-branch Changes by: mmitchel@gcc.gnu.org 2003-03-23 22:55:51 Modified files: gcc : ChangeLog fold-const.c gcc/testsuite : ChangeLog Added files: gcc/testsuite/gcc.dg: 20030323-1.c Log message: PR c/8224 * fold-const.c (extract_muldiv_1): Don't pass through type conversions when signedness changes for division or modulus. PR c/8224 * gcc.dg/20030323-1.c: New test. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.16114.2.346&r2=1.16114.2.347 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/fold-const.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.227.2.2&r2=1.227.2.3 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=1.2261.2.109&r2=1.2261.2.110 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/20030323-1.c.diff?cvsroot=gcc&only_with_tag=gcc-3_3-branch&r1=NONE&r2=1.1.2.1

From: mmitchel@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: c/8224 Date: 23 Mar 2003 22:57:26 -0000 CVSROOT: /cvs/gcc Module name: gcc Changes by: mmitchel@gcc.gnu.org 2003-03-23 22:57:26 Modified files: gcc : ChangeLog fold-const.c gcc/testsuite : ChangeLog Added files: gcc/testsuite/gcc.dg: 20030323-1.c Log message: PR c/8224 * fold-const.c (extract_muldiv_1): Don't pass through type conversions when signedness changes for division or modulus. PR c/8224 * gcc.dg/20030323-1.c: New test. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=1.17195&r2=1.17196 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/fold-const.c.diff?cvsroot=gcc&r1=1.241&r2=1.242 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.2527&r2=1.2528 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/20030323-1.c.diff?cvsroot=gcc&r1=1.1&r2=1.2

From: ebotcazou@gcc.gnu.org To: gcc-gnats@gcc.gnu.org Cc: Subject: c/8224 Date: 29 Mar 2003 10:29:33 -0000 CVSROOT: /cvs/gcc Module name: gcc Branch: gcc-3_2-branch Changes by: ebotcazou@gcc.gnu.org 2003-03-29 10:29:33 Modified files: gcc : ChangeLog fold-const.c gcc/testsuite : ChangeLog Added files: gcc/testsuite/gcc.dg: 20030323-1.c Log message: PR c/8224 * fold-const.c (extract_muldiv_1): Don't pass through type conversions when signedness changes for division or modulus. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=1.13152.2.657.2.289&r2=1.13152.2.657.2.290 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/fold-const.c.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=1.185.2.4.2.6&r2=1.185.2.4.2.7 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=1.1672.2.166.2.121&r2=1.1672.2.166.2.122 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/20030323-1.c.diff?cvsroot=gcc&only_with_tag=gcc-3_2-branch&r1=NONE&r2=1.2.4.1

Bug#: 8224	Product: gcc	Version: 3.2
Host:	Target:	Build:
Status: RESOLVED	Severity: normal	Priority: P3
Resolution: FIXED	Assigned To: unassigned@gcc.gnu.org	Reported By: mikulas@artax.karlin.mff.cuni.cz
Component: c		Target Milestone: ---
Summary: Incorrect joining of signed and unsigned division
Keywords: wrong-code
Opened: 2002-10-14 07:36