[Bug rtl-optimization/41085] New: [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[Bug rtl-optimization/41085] New: [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

With revision r149958 this test passed.
>From revision r149962 (i.e. the revision introducing the regression) and on,
this test has failed as follows:

Running /tmp/r149958-149962/gcc/gcc/testsuite/gcc.dg/dg.exp ...
...
FAIL: gcc.dg/pr28796-2.c execution test

With the message in the logfile being:

Executing on host: /tmp/r149958-149962/gccobj/gcc/xgcc
-B/tmp/r149958-149962/gccobj/gcc/ /tmp/r149958-149962/gcc/gcc/tes
tsuite/gcc.dg/pr28796-2.c   -O2 -funsafe-math-optimizations
-fno-finite-math-only -DUNSAFE   -isystem /tmp/r149958-14996
2/gccobj/cris-elf/./newlib/targ-include -isystem
/tmp/r149958-149962/gcc/newlib/libc/include -B/tmp/r149958-149962/gccob
j/cris-elf/./libgloss/cris/
-L/tmp/r149958-149962/gccobj/cris-elf/./libgloss/cris
-L/tmp/r149958-149962/gcc/libgloss/cri
s  -B/tmp/r149958-149962/gccobj/cris-elf/./newlib/
-L/tmp/r149958-149962/gccobj/cris-elf/./newlib -sim3  -lm   -o ./pr28
796-2.exe    (timeout = 300)
PASS: gcc.dg/pr28796-2.c (test for excess errors)
program stopped with signal 6.
FAIL: gcc.dg/pr28796-2.c execution test

I'll attach a reduced test-case and a description of the wrong code.

Author of patch exposing the regression CC:ed.


-- 
           Summary: [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hp at gcc dot gnu dot org
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: cris-axis-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #1 from hp at gcc dot gnu dot org  2009-08-17 03:44 -------
Created an attachment (id=18376)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18376&action=view)
Simplified gcc.dg/pr28796-2.c

It's the fourth call to foo that has its "d" parameter (passed in r10 and r11)
munged to 0, where r11 should have held 0x100000, just like r13 (parameter
"ld", passed in r12 and r13 and long double === double for this target).

If you look at the generated code, there's a little song-and-dance storing the
variables temporarily to stack because of the "volatile" qualifier, but which
seemingly improved with r149962.  To wit, the lines
  d = ((double)2.2250738585072014e-308L); ld = 2.2250738585072014e-308L;
  foo(d, ld, 0, 1);
are compiled as:
  d = 0; ld = 2.2250738585072014e-308L;
  foo(d, ld, 0, 1);

Deleting further individual statements or parameters or the volatile qualifiers
(any combination I tried) hid the bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[vmakarov at redhat dot com]

------- Comment #2 from vmakarov at redhat dot com  2009-08-17 15:13 -------
Thanks for reporting this bug.

I've looked at the code and I think the patch in question probably triggered
some latent reload bug.  All wrong code transformations are done in reload.

Although I think assigning r8 to pseudo 47 could result in wrong reload
behaviour because r8 is used as a frame pointer even before the RA.  It looks
very strange to me that r8 used as a frame pointer is *not a fixed* register. 
If I wrote the port, I'd rather use a virtual register for the frame pointer
and eliminate it into hard frame pointer register (r8) or to stack pointer as
all other ports do.  This probably would solve the problem.

So I see the 2 solution right now:
  1. make r8 fixed which is not so good because it eliminates it from RA when
     we use only sp for stack addressing
  2. use virtual frame pointer and eliminate it into r8 or sp.

The first solution is the simplest one, the second is more right, IMHO.

I'll be unavailable till the end of Aug.  So our discussion will be delayed. 
Sorry for that.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #3 from hp at gcc dot gnu dot org  2009-08-17 16:32 -------
(In reply to comment #2)
> Although I think assigning r8 to pseudo 47 could result in wrong reload
> behaviour because r8 is used as a frame pointer even before the RA.  It looks
> very strange to me that r8 used as a frame pointer is *not a fixed* register.

There's nothing wrong with that in a port, besides trigging reload bugs, that
is.  ...and now that you mention it, I guess it might inconvenience the
register allocator.

> If I wrote the port, I'd rather use a virtual register for the frame pointer
> and eliminate it into hard frame pointer register (r8) or to stack pointer as
> all other ports do.

Not all ports, e.g. the m68k port does the same (A6).  IMHO, requiring to
*manually* allocate a virtual frame-pointer in a port only to eliminate it to a
hard register is a wart; it's just complicating the port where middle-end gcc
could do the work.

> This probably would solve the problem.

I'd say it would cover it up, not solve it.

But thanks for looking, I'll have another look myself and try and see if I can
fix the actual reload bug.  I'm not ruling out eventually using a virtual frame
pointer, albeit pragmatically a fix, it just doesn't strike me as TRT.


-- 

hp at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |hp at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-08-17 16:32:08
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5 Regression]: cris-elf gcc.dg/pr28796-2.c

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-04-06 11:20 -------
GCC 4.5.0 is being released.  Deferring to 4.5.1.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.0                       |4.5.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #5 from hp at gcc dot gnu dot org  2010-07-24 03:14 -------
This regression disappeared in the range (162414:162421], perhaps because of
r162418. Let's see if it remains hidden, or if this PR just shapeshifted into
PR45051.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #6 from hp at gcc dot gnu dot org  2010-07-24 03:16 -------
Unassigning myself as I haven't done and won't do anything besides observing.


-- 

hp at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|hp at gcc dot gnu dot org   |unassigned at gcc dot gnu
                   |                            |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2010-07-31 09:29 -------
GCC 4.5.1 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.1                       |4.5.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #8 from hp at gcc dot gnu dot org  2010-09-11 04:33 -------
(In reply to comment #5)
> This regression disappeared in the range (162414:162421], perhaps because of
> r162418. Let's see if it remains hidden, or if this PR just shapeshifted into
> PR45051.

I (finally) checked this hunch of mine, and the fix for PR45051 indeed fixes
this PR too!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #9 from hp at gcc dot gnu dot org  2010-09-21 21:26 -------
Subject: Bug 41085

Author: hp
Date: Tue Sep 21 21:25:57 2010
New Revision: 164498

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=164498
Log:
        PR rtl-optimization/41085
        Backport from mainline
        2010-07-27  Bernd Schmidt  <bernds@codesourcery.com>

        PR rtl-optimization/45051
        * reload1.c (delete_output_reload): Use refers_to_regno_p rather
        than reg_mentioned_p.

Modified:
    branches/gcc-4_5-branch/gcc/ChangeLog
    branches/gcc-4_5-branch/gcc/reload1.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085

[Bug rtl-optimization/41085] [4.5/4.6 Regression]: cris-elf gcc.dg/pr28796-2.c

[hp at gcc dot gnu dot org]

------- Comment #10 from hp at gcc dot gnu dot org  2010-09-21 21:30 -------
.


-- 

hp at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41085