[Bug tree-optimization/38405] New: Regression (silent failure) handling bitfield in ternary

[Bug tree-optimization/38405] New: Regression (silent failure) handling bitfield in ternary

[gcc-bugzilla at gcc dot gnu dot org]

        In the context of a function returning int, and rfp->signed is a
one-bit field,
        return rfp->signed_flag ? 1 : 0;
        yields -1.  This is an optimization problem, seen with -O2 but not -O1.
        Isolated to -ftree-vrp.  Not seen in gcc-4.3 or earlier.

Environment:
System: Linux recycle 2.6.26-1-amd64 #1 SMP Sat Oct 18 15:27:18 UTC 2008 x86_64
GNU/Linux



host: x86_64-pc-linux-gnu
build: x86_64-pc-linux-gnu
target: x86_64-pc-linux-gnu
configured with: ../src/configure -v --with-pkgversion='Debian 20081130-1'
--with-bugurl=file:///usr/share/doc/gcc-snapshot/README.Bugs
--enable-languages=c,c++,java,fortran,objc,obj-c++,ada
--prefix=/usr/lib/gcc-snapshot --enable-shared --with-system-zlib --disable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-java-awt=gtk
--enable-gtk-cairo --disable-plugin
--with-java-home=/usr/lib/gcc-snapshot/java-1.5.0-gcj-4.4-1.5.0.0/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/gcc-snapshot/jvm
--with-jvm-jar-dir=/usr/lib/gcc-snapshot/jvm-exports
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-mpfr
--enable-cld --disable-werror --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu

How-To-Repeat:

Short way:

$ gcc -Wall -O1 -ftree-vrp ternbug.c -o ternbug && ./ternbug
Hello world: -1
FAIL
$ 

Long way:

$ /usr/lib/gcc-snapshot/libexec/gcc/x86_64-linux-gnu/4.4.0/cc1 -fpreprocessed
ternbug.i -quiet -dumpbase ternbug.c -mtune=generic -auxbase ternbug -O1
-ftree-vrp -version -o ternbug.s
GNU C (Debian 20081130-1) version 4.4.0 20081130 (experimental) [trunk revision
142292] (x86_64-linux-gnu)
        compiled by GNU C version 4.4.0 20081130 (experimental) [trunk revision
142292], GMP version 4.2.2, MPFR version 2.3.2.
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: ef8facef55b835d47393957737fa78a4
$ as -V -Qy -o ternbug.o ternbug.s
GNU assembler version 2.18.0 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Debian) 2.18.0.20080103
$ /usr/lib/gcc-snapshot/libexec/gcc/x86_64-linux-gnu/4.4.0/collect2
--eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o
ternbug /usr/lib/../lib/crt1.o /usr/lib/../lib/crti.o
/usr/lib/gcc-snapshot/lib/gcc/x86_64-linux-gnu/4.4.0/crtbegin.o
-L/usr/lib/gcc-snapshot/lib/gcc/x86_64-linux-gnu/4.4.0
-L/usr/lib/gcc-snapshot/lib/gcc/x86_64-linux-gnu/4.4.0/../../../../lib
-L/lib/../lib -L/usr/lib/../lib
-L/usr/lib/gcc-snapshot/lib/gcc/x86_64-linux-gnu/4.4.0/../../.. ternbug.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc-snapshot/lib/gcc/x86_64-linux-gnu/4.4.0/crtend.o
/usr/lib/../lib/crtn.o
$ ./ternbug
Hello world: -1
FAIL
$ 

Minimal test case, ternbug.{c,i}:

extern int printf (__const char *__restrict __format, ...);

struct vpiBinaryConst {
 int signed_flag :1;
 int sized_flag :1;
};

int binary_get(int code, struct vpiBinaryConst *rfp)
{
 switch (code) {
  case 1:
   return rfp->signed_flag ? 1 : 0;
  default:
   printf("error: %d not supported\n", code);
   return 0;
 }
}


------- Comment #1 from ldoolitt at recycle dot lbl dot gov  2008-12-04 17:36 -------
Fix:
        Work around by reducing optimization, e.g., from -O2 to -O1


-- 
           Summary: Regression (silent failure) handling bitfield in ternary
           Product: gcc
           Version: 4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ldoolitt at recycle dot lbl dot gov
 GCC build triplet: x86_64-pc-linux-gnu
  GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] Regression (silent failure) handling bitfield in ternary

[ldoolitt at recycle dot lbl dot gov]

------- Comment #2 from ldoolitt at recycle dot lbl dot gov  2008-12-04 17:45 -------
Created an attachment (id=16827)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16827&action=view)
test case source (preprocessed)

Test case source in "how to reproduce" got chopped.  Sorry.  Here it is in the
form of an attachment.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] Regression (silent failure) handling bitfield in ternary

[hjl dot tools at gmail dot com]

------- Comment #3 from hjl dot tools at gmail dot com  2008-12-04 20:35 -------
It is caused by revision 140288:

http://gcc.gnu.org/ml/gcc-patches/2008-08/msg01925.html


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bonzini at gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[hjl dot tools at gmail dot com]

-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl dot tools at gmail dot
                   |                            |com
            Summary|Regression (silent failure) |[4.4 Regression] (silent
                   |handling bitfield in ternary|failure) handling bitfield
                   |                            |in ternary
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[bonzini at gnu dot org]

------- Comment #4 from bonzini at gnu dot org  2008-12-05 09:02 -------
I'll look at it in a couple of days.  In the meanwhile, could you please attach
the dumps of vrp and the pass just before it?


-- 

bonzini at gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |bonzini at gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-12-05 09:02:53
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2008-12-05 11:23 -------
The error is likely

Folding statement: D.1241_5 = D.1242_4 != 0;
Folded into: D.1241_5 = (int) D.1242_4;

which is wrong for

  <unnamed-signed:1> D.1242;

because it sign-extends.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.3.2
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[bonzini at gnu dot org]

------- Comment #6 from bonzini at gnu dot org  2008-12-05 15:42 -------
Subject: Re:  [4.4 Regression] (silent failure)
 handling bitfield in ternary


> Folding statement: D.1241_5 = D.1242_4 != 0;
> Folded into: D.1241_5 = (int) D.1242_4;
> 
> which is wrong for
> 
>   <unnamed-signed:1> D.1242;
> 
> because it sign-extends.

So it's probably in fold-const.c and latent in 4.3 too...

Paolo


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[hjl dot tools at gmail dot com]

------- Comment #7 from hjl dot tools at gmail dot com  2008-12-07 16:17 -------
This bug disappeared between revision 142341 and revision 142508.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2008-12-07 16:29 -------
Maybe it's just gone latent ...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[hjl at gcc dot gnu dot org]

------- Comment #9 from hjl at gcc dot gnu dot org  2008-12-07 16:44 -------
Subject: Bug 38405

Author: hjl
Date: Sun Dec  7 16:43:15 2008
New Revision: 142538

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=142538
Log:
2008-12-07  H.J. Lu  <hongjiu.lu@intel.com>

        PR tree-optimization/38405
        * gcc.dg/torture/pr38405.c: New.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr38405.c
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[hjl dot tools at gmail dot com]

------- Comment #10 from hjl dot tools at gmail dot com  2008-12-07 17:17 -------
It is fixed by revision 142483:

http://gcc.gnu.org/ml/gcc-patches/2008-12/msg00341.html


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[hjl dot tools at gmail dot com]

------- Comment #11 from hjl dot tools at gmail dot com  2008-12-07 17:39 -------
Oops. It is revision 142484:

http://gcc.gnu.org/ml/gcc-patches/2008-12/msg00340.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2008-12-07 18:52 -------
We now get

  D.1254 = BIT_FIELD_REF <*rfp, 8, 0>;
  D.1255 = D.1254 & 1;
  D.1253 = D.1255 != 0;

which causes missed optimizations.  Jakub - can you disable the bit-field-ref
folding for single tests like this?


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2008-12-07 19:20 -------
It's not fixed.  Jakub just made it latent.  I am testing a real fix.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #15 from rguenth at gcc dot gnu dot org  2008-12-07 20:34 -------
Subject: Bug 38405

Author: rguenth
Date: Sun Dec  7 20:33:07 2008
New Revision: 142539

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=142539
Log:
2008-12-07  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/38405
        * tree-vrp.c (simplify_truth_ops_using_ranges): Make sure to
        not sign-extend truth values.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-vrp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405

[Bug tree-optimization/38405] [4.4 Regression] (silent failure) handling bitfield in ternary

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2008-12-07 20:33 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38405