[Bug optimization/11937] New: bogus warning while compiling gcc/function.c

[Bug optimization/11937] New: bogus warning while compiling gcc/function.c

[gcc-bugzilla at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937

           Summary: bogus warning while compiling gcc/function.c
           Product: gcc
           Version: 3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: uwe at netbsd dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-unknown-freebsd4.8
  GCC host triplet: i386-unknown-freebsd4.8
GCC target triplet: shle--netbsdelf


I'm using this compiler to compile the same version of the gcc for
NetBSD/hcpsh

host: shle--netbsdelf
build: i386--freebsd4.8 
target: shle--netbsdelf

configured with: ../configure --prefix=/var/tmp/xtarget --target=shle--netbsdelf --host=shle--netbsdelf --build=i386--freebsd4.8 --disable-multilib --disable-shared --enable-languages=c

While compiling function.c the warning about `and' of mutually
exclusive equal-tests is always 0 is produced:

shle--netbsdelf-gcc -save-temps -c -g -O2 -DIN_GCC   -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long   -DHAVE_CONFIG_H    -I. -I. -I../../gcc -I../../gcc/. -I../../gcc/config -I../../gcc/../include ../../gcc/function.c -o function.o
../../gcc/function.c: In function `aggregate_value_p':
../../gcc/function.c:4283: warning: suggest parentheses around && within ||
../../gcc/function.c: In function `assign_parms':
../../gcc/function.c:4740: warning: `and' of mutually exclusive equal-tests is always 0

I saw this warning with gcc-3.3 release and also with gcc-3.3.1
release as imported into the NetBSD source tree.

The warning is triggered by turning optimization on.  Compiling with
-O0 doesn't produce the warning.

The warning about line 4283 is not present for 3.3 and 3.3.1 releases
and is not pertinent to this bug report.

The offending line is:

    else if (PARM_BOUNDARY % BITS_PER_WORD != 0)

that expands to:

    else if (((target_flags & (1<<0)) ? 64 : 32) % (8 * (((target_flags & (1<<0)) && ! (target_flags & (1<<8))) ? 8 : 4)) != 0)


In particular the following subexpression causes the warning:

    ((target_flags & (1<<0)) && ! (target_flags & (1<<8)))

which is just the TARGET_SHMEDIA macro that is used all over the place
without any problems.

I did some debugging (sorry, but I know next to nothing about gcc
internals) and if I'm reading the output of dump_node correctly, the
fold-const.c:fold_truthop() complains about the tree that corresponds
to the following C expression:

    ((target_flags & 0x101) == 1) && ((target_flags & 1) == 0)

where the first occurence of `target_flags' is actually a
bit_field_ref node.

Now, the lhs of this `and' is the correct folding of the

    ((target_flags & (1<<0)) && ! (target_flags & (1<<8)))

TARGET_SHMEDIA macro, but I have no idea where the rhs comes from.

After looking through the ChangeLog I thought that might be some
shared structures are modified, so I tried to apply the fix from the
gcc-3_3-rhl-branch:

        * fold-const.c (fold): Never modify argument passed to fold, instead
        change a copy and return it.
        * convert.c (convert_to_integer): Likewise.

by pulling the following diffs:

    convert.c: 1.19 -> 1.19.18.1
    fold-constant.c: 1.227.2.3.4.1 -> 1.227.2.3.4.2
    
but that didn't help (same warning) and didn't produce any errors with
ENABLE_FOLD_CHECKING.

This warning seems to indicate a bug in optimizer.

gcc-3.4-20030813 snapshot does not have this problem.

However, since the next release of NetBSD will be using gcc 3.3.1 as
the system compiler, it would be very nice to have a fix or a
work-around for this bug on the 3.3 branch.

Environment:
System: FreeBSD vortex.sparc.spb.su 4.8-STABLE FreeBSD 4.8-STABLE #0: Wed Jun 4 13:52:39 MSD 2003 root@vortex.sparc.spb.su:/usr/obj/usr/src/sys/VORTEX i386

host: i386-unknown-freebsd4.8
build: i386-unknown-freebsd4.8
target: shle--netbsdelf
configured with: ../configure --prefix=/var/tmp/xtools --target=shle--netbsdelf --disable-multilib --disable-shared --enable-languages=c

How-To-Repeat:

With a gcc from the 3.3 branch targeting shle--netbsdelf (probably,
any SuperH target) try to compile the following file:

[Bug optimization/11937] bogus warning while compiling gcc/function.c

[uwe at netbsd dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From uwe at netbsd dot org  2003-08-16 00:45 -------
Created an attachment (id=4614)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=4614&action=view)
Source file that demonstrates the problem.

Oops, it seems that the uuencoded file I included into the PR didn't make it to
bugzilla.

[Bug optimization/11937] [3.3 only] bogus warning while compiling gcc/function.c

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
            Summary|bogus warning while         |[3.3 only] bogus warning
                   |compiling gcc/function.c    |while compiling
                   |                            |gcc/function.c
   Target Milestone|---                         |3.3.3


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-08-16 00:48 -------
Do you know if this is a regression from an earlier GCC?

[Bug optimization/11937] [3.3 only] bogus warning while compiling gcc/function.c

[uwe at netbsd dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From uwe at netbsd dot org  2003-08-16 00:56 -------
Subject: Re:  [3.3 only] bogus warning while compiling gcc/function.c

gcc-2.95.3 (system compiler) that is used to build this gcc-3.3.1
sources as a cross compiler targeting superh compiles this file
without that warning.

when the resulting gcc-3.3.1 is used to compile the same gcc-3.3.1
sources as the native compiler to be run on the superh host, I get
this warning.

So this is a regression from 2.95 series.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[3.3 only] bogus warning    |[3.3 Regression] bogus
                   |while compiling             |warning while compiling
                   |gcc/function.c              |gcc/function.c


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-08-16 01:04 -------
Thanks I do not know if it is going to be fixed for 3.3.x as it is already fixed in 3.4.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
  GCC build triplet|i386-unknown-freebsd4.8     |
   GCC host triplet|i386-unknown-freebsd4.8     |
 GCC target triplet|shle--netbsdelf             |
   Last reconfirmed|0000-00-00 00:00:00         |2003-08-16 01:17:43
               date|                            |


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-08-16 01:17 -------
I can reproduce the following warning on powerpc-apple-darwin6.6 in 3.3.2 (20030815):
test1.c: In function `f':
test1.c:6: warning: `and' of mutually exclusive equal-tests is always 0

It also happens on i686-pc-linux-gnu.


The code:
int target_flags;

int f()
{ 
return 
(((target_flags & (1<<0)) ? 64 : 32) % (8 * (((target_flags & (1<<0)) && ! (target_flags & (1<<8))) ? 8 
: 4)) != 0)
;
}

It does not happen in 3.1 (20020420).
Broken : Search converges between 2002-06-02-trunk (#80) and 2002-07-14-trunk (#81).
Fixed: Search converges between 2003-07-02-trunk (#331) and 2003-07-03-trunk (#332).


Here are two changes on the July 2 which might have fixed this:
2003-07-02  Jeff Law   <-- this one needs another patch fix fix a regression which it caused

        * expr.c (do_store_flag): Remove special case folding for
        single bit tests.  Instead call back into the commonized folder
        routine.
        * fold-const.c (fold_single_bit_test): New function, mostly
        extracted from do_store_flag, with an additional case extracted
        from fold.
        (fold): Call fold_single_bit_test appropriately.
        * tree.h (fold_single_bit_test): Prototype.

2003-07-02  Eric Botcazou

        PR optimization/11210
        * expr.c (handled_component_p) [NOP_EXPR]: Add ??? note
        about the behaviour with regard to bitfields.     
        * fold-const (decode_field_reference): Record outermost type in
        case the expression is a NOP. Strip all NOPs. Set the signedness
        to that of the outermost type (if any) when the bitsize is equal
        to the size of the type.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[uwe at ptc dot spbu dot ru]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From uwe at ptc dot spbu dot ru  2003-08-16 01:26 -------
Subject: Re:  [3.3 Regression] bogus warning while compiling gcc/function.c

Doh.  I tried to come up with a minimal test case like this, but
neither my test, nor yours give me the warning.

Thanks a lot, I will try those changes.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[uwe at ptc dot spbu dot ru]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From uwe at ptc dot spbu dot ru  2003-08-16 02:18 -------
Subject: Re:  [3.3 Regression] bogus warning while compiling gcc/function.c

The warning goes away after applying

expr.c:		1.561, 1.562
fold-const.c:	1.273, 1.276
tree.h:		1.419

to the gcc-3.3 branch (patches applied cleanly, with offset).

Relevant changelog entries:

2003-07-04  Jeff Law  <law@redhat.com>

        PR c/11428
        * expr.c (do_store_flag): Pass in the correct result type
        when calling fold_single_bit_test.
        * fold-const.c (fold_single_bit_test): Use result_type for the
        result when folding a sign bit test.

2003-07-02  Jeff Law  <law@redhat.com>

        * expr.c (do_store_flag): Remove special case folding for
        single bit tests.  Instead call back into the commonized folder
        routine.
        * fold-const.c (fold_single_bit_test): New function, mostly
        extracted from do_store_flag, with an additional case extracted
        from fold.
        (fold): Call fold_single_bit_test appropriately.
        * tree.h (fold_single_bit_test): Prototype.

Thanks!

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[uwe at ptc dot spbu dot ru]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From uwe at ptc dot spbu dot ru  2003-08-16 02:25 -------
Subject: Re:  [3.3 Regression] bogus warning while compiling gcc/function.c

On Sat, Aug 16, 2003 at 06:18:50 +0400, Valeriy E. Ushakov wrote:


> The warning goes away after applying
> 
> expr.c:		1.561, 1.562
> fold-const.c:	1.273, 1.276
> tree.h:		1.419

It probably also needs fold-const.c 1.280, as c/11449 blames
fold-const.c 1.273

2003-07-10  Kazu Hirata  <kazu@cs.umass.edu>

        PR c/11449
        * fold-const.c (sign_bit_p): Return EXP if VAL is the sign bit
        of HOST_WIDE_INT.
        (fold_single_bit_test): If sign_bit_p() fails, assume that the
        bit being tested is not a sign bit.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at redhat dot com


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-08-16 02:26 -------
Thanks for looking into it and finding the patch which fixes it.

Jeff could ask for inclusion for 3.3.2?
<http://gcc.gnu.org/ml/gcc-patches/2003-07/msg00299.html>

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.3.3                       |3.3.2

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[mmitchel at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937



------- Additional Comments From mmitchel at gcc dot gnu dot org  2003-09-05 07:18 -------
If someone would post the exact patch to review for 3.3.2, that would be great.

[Bug optimization/11937] [3.3 Regression] bogus warning while compiling gcc/function.c

[mmitchel at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11937


mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


------- Additional Comments From mmitchel at gcc dot gnu dot org  2003-10-16 09:27 -------
The changes required are too invasive for GCC 3.3.x.