[Bug c/26436] New: Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[Bug c/26436] New: Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

While trying to build matplotlib-0.87 on HP-UX 11.23/IA-64 with gcc-3.4.3:
gcc -fno-strict-aliasing -DNDEBUG -D_FILE_OFFSET_BITS=64 -O2
-I/opt/TWWfsw/python235p/include/python2.3 -fPIC -I/opt/TWWfsw/libttf21/include
-I/opt/TWWfsw/libpng12/include -I/opt/TWWfsw/zlib11/include -I.
-I/opt/TWWfsw/python235/include/python2.3 -c src/_nc_cntr.c -o
build/temp.hp-ux-B.11.23-ia64-2.3/src/_nc_cntr.o -DNUMERIC=1
/var/tmp//ccPC8aab.s: Assembler messages:
/var/tmp//ccPC8aab.s:1186: Warning: Use of 'mov' may violate WAW dependency
'GR%, % in 1 - 127' (impliedf), specific resource number is 14
/var/tmp//ccPC8aab.s:1186: Warning: Only the first path encountering the
conflict is reported
/var/tmp//ccPC8aab.s:1185: Warning: This is the location of the conflicting
usage
/var/tmp//ccPC8aab.s:2016: Warning: Use of 'mov' may violate WAW dependency
'GR%, % in 1 - 127' (impliedf), specific resource number is 14
/var/tmp//ccPC8aab.s:2016: Warning: Only the first path encountering the
conflict is reported
/var/tmp//ccPC8aab.s:2015: Warning: This is the location of the conflicting
usage


-- 
           Summary: Use of 'mov' may violate WAW dependency 'GR%, % in 1 -
                    127' (impliedf), specific resource number is 14
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bugzilla-gcc at thewrittenword dot com
 GCC build triplet: ia64-hp-hpux11.23
  GCC host triplet: ia64-hp-hpux11.23
GCC target triplet: ia64-hp-hpux11.23


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug c/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #1 from bugzilla-gcc at thewrittenword dot com  2006-02-23 00:16 -------
Created an attachment (id=10893)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10893&action=view)
.s file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug c/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #2 from bugzilla-gcc at thewrittenword dot com  2006-02-23 00:16 -------
Created an attachment (id=10894)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10894&action=view)
.i file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2006-02-23 01:34 -------
What version of binutils are you using?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #4 from bugzilla-gcc at thewrittenword dot com  2006-02-23 01:38 -------
$ /opt/TWWfsw/gcc343/ia64-hp-hpux11.23/bin/as --version
GNU assembler 2.16
Copyright 2005 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License.  This program has absolutely no warranty.
This assembler was configured for a target of `ia64-hp-hpux11.23'.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #5 from bugzilla-gcc at thewrittenword dot com  2006-02-23 01:39 -------
Looking at gas/Changelog between 2.16 and 2.16.1, I see:
  2005-05-19  Jan Beulich  <jbeulich@novell.com>

          * config/tc-ia64.c (dot_endp): Don't use global symbol for unwind
          relocations in unwind section.

Dunno if this makes a difference. I'm building gcc-4.0.2 with binutils-2.16.1
now.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #6 from bugzilla-gcc at thewrittenword dot com  2006-02-23 02:38 -------
Created an attachment (id=10896)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10896&action=view)
.s file (gcc-4.0.2 with as 2.16.1)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #7 from bugzilla-gcc at thewrittenword dot com  2006-02-23 02:39 -------
Created an attachment (id=10897)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10897&action=view)
.i file (gcc-4.0.2 with as 2.16.1)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #8 from bugzilla-gcc at thewrittenword dot com  2006-02-23 02:41 -------
gcc-4.0.2 with either as 2.16/2.16.1 generates no warning.
gcc-3.4.3 with either as 2.16/2.16.1 generates the warning.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[pinskia at gcc dot gnu dot org]

------- Comment #9 from pinskia at gcc dot gnu dot org  2006-02-23 02:56 -------
Can you try 3.4.5?


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Use of 'mov' may violate WAW|[3.4 only] Use of 'mov' may
                   |dependency 'GR%, % in 1 -   |violate WAW dependency 'GR%,
                   |127' (impliedf), specific   |% in 1 - 127' (impliedf),
                   |resource number is 14       |specific resource number is
                   |                            |14
   Target Milestone|---                         |3.4.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #10 from bugzilla-gcc at thewrittenword dot com  2006-02-23 03:02 -------
Sure. It might take a few days.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[bugzilla-gcc at thewrittenword dot com]

------- Comment #11 from bugzilla-gcc at thewrittenword dot com  2006-02-24 22:03 -------
(In reply to comment #9)
> Can you try 3.4.5?

Same problem as 3.4.3.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[wilson at gcc dot gnu dot org]

------- Comment #12 from wilson at gcc dot gnu dot org  2006-02-28 02:13 -------
This looks like an assembler problem to me, and a known one at that.

The assembly code in question, somewhat simplified, is 
        .pred.rel.mutex p8, p9
        (p9) cmp4.lt p6, p7 = 1, r38
        (p8) cmp4.gt p6, p7 = -1, r38
        ;;
        (p6) addl r14 = 1, r0
        (p7) mov r14 = r0
The assembler should be able to figure out that this is safe.  Unfortunately,
the dependency violation checking code in the assembler was never finished. 
The problem is far harder than we originally thought, and the current code
can't handle complicated nested cases like this.  I estimate that fixing the
general problem is 1 month of work if I do the job, and 2 months if anyone else
does it.  Since IA-64 work is a hobby for me, it is unlikely I will tackle a
job this large.  Maybe this specific problem is simpler to fix than the general
case, but I'm reluctant to go that way.  I would prefer that the code be
rewritten from scratch, properly, rather than add hacks for special cases.

I suspect that the problem does not occur with gcc-4.x, because somewhere along
the line, someone made it stupider in order to fix a bug, and it no longer
generates the complicated nested DV cases that the assembler can't handle. 
Trying "grep ') cmp' test.s | wc" with the two testcases to find predicated
compare instructions gives 32 for the gcc-3.4 compiled one, and 11 for the
gcc-4.0 compiled one.

Actually, looking closely, I do see one possible problematic sequence in the
gcc-4.0 output, but it is immediately followed by a branch, and this forces the
compiler to insert a .pred.rel.mutex directive at the target label.  Thus the
gcc-4.0 output assembles cleanly, but this may just be a happy accident.

As a workaround, we could modify the compiler to try to detect nested DV cases,
and emit extra unnecessary .pred.rel.mutex directives for them.  This would
work around the assembler bug.  This isn't the best solution, but may be
simpler than trying to fix the assembler.


-- 

wilson at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[gdr at integrable-solutions dot net]

------- Comment #13 from gdr at integrable-solutions dot net  2006-02-28 09:02 -------
Subject: Re:  [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 -
127' (impliedf), specific resource number is 14

"wilson at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

[...]

| As a workaround, we could modify the compiler to try to detect nested DV
cases,
| and emit extra unnecessary .pred.rel.mutex directives for them.  This would
| work around the assembler bug.

Jim, you seem to understand well the issue.  Would you ve willing to
contribute a patch?  GCC-3.4.6 release is soon; otherwise, I will just
close this PR as won't fix.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[gdr at gcc dot gnu dot org]

------- Comment #14 from gdr at gcc dot gnu dot org  2006-03-01 10:13 -------
unlikey to be fixed for 3.4.6.


-- 

gdr at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436

[Bug target/26436] [3.4 only] Use of 'mov' may violate WAW dependency 'GR%, % in 1 - 127' (impliedf), specific resource number is 14

[wilson at gcc dot gnu dot org]

------- Comment #15 from wilson at gcc dot gnu dot org  2006-03-02 00:06 -------
Created an attachment (id=10952)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10952&action=view)
not recommended prototype patch to avoid assembler bug

I have a gcc-3.4.x patch that silences the assembler warnings for the testcase.
 However, I am not particularly happy about it.  It doesn't handle every
possible case.  Also, it doesn't attempt to verify that the predicate registers
are mutex.  It just emits a directive to disable the assembler warning.  In the
worst case, this could mask a gcc bug that would otherwise be found by the
assembler DV checks.  I haven't done any testing on this, other than running it
on the testcase.

I think it would be best if the problem was fixed in the assembler.  Meanwhile,
if you get suspicious assembler warnings, you can check the assembly code
yourself to see if there is a real problem, or if this is an assembler bug.  Or
if you are desperate, you can try using this patch.

I don't plan to do any further work on this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26436