[Bug debug/47881] New: [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[Bug debug/47881] New: [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

           Summary: [4.6 Regression] -fcompare-debug failure (length) with
                    -O -fno-dce -funroll-loops -fno-web
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zsojka@seznam.cz
                CC: aoliva@gcc.gnu.org
              Host: i686-pc-linux-gnu
            Target: i686-pc-linux-gnu


Created attachment 23452
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23452
reduced testcase

Compiler output:
$ gcc -O -fcompare-debug -fno-dce -funroll-loops -fno-web testcase.c -m32
gcc: error: testcase.c: -fcompare-debug failure (length)

$ diff testcase.*gkd
943c943
< (insn# 0 0 39 (set (reg:SI 4 si)
---
> (insn# 0 0 39 (set (reg:SI 5 di)
947,948c947,948
<             (set (reg:SI 4 si)
<                 (plus:SI (reg:SI 4 si)
---
>             (set (reg:SI 5 di)
>                 (plus:SI (reg:SI 5 di)
...

Tested revisions:
r170450 - fail
4.5 r170013 - OK
4.5.2 - OK

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

Steven Bosscher <steven at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.03.06 13:55:09
                 CC|                            |steven at gcc dot gnu.org
     Ever Confirmed|0                           |1

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-07 10:12:04 UTC ---
While this started with
http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=167390,
it looks just as it uncovered a latent IRA bug.
My guess is that the differences are related to ira-emit.c (change_loop)
creating
some new pseudos, whose live ranges then don't ignore debug insns (normally
debug insns would be changed or reset to avoid different lr ranges caused by
debug insns, but probably as this happens still within IRA it won't be
adjusted).

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-07 11:32:53 UTC ---
Problems start when the combiner leaves in a trivially dead insn by substing it
later on in some subsequent insn.  Nothing until IRA calls
delete_trivially_dead_insns, and when IRA calls it, it removes that insn, which
effectively shortens the lifetime of one of the pseudos.  Unfortunately that
psuedo is set multiple times (probably -funroll-loops is the reason), so
delete_trivially_dead_insns isn't trying to reset or change related debug
insns, it doesn't have enough infrastructure to do so.  Normally DF would then
reset them, but DF isn't recomputed until IRA finishes.

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-07 11:41:17 UTC ---
--- gcc/ira.c.jj    2011-02-21 15:37:42.000000000 +0100
+++ gcc/ira.c    2011-03-07 12:33:59.000000000 +0100
@@ -3232,7 +3232,8 @@ ira (FILE *f)
     check_allocation ();
 #endif

-  delete_trivially_dead_insns (get_insns (), max_reg_num ());
+  if (delete_trivially_dead_insns (get_insns (), max_reg_num ()))
+    df_analyze ();

   init_reg_equiv_memory_loc ();

indeed fixes this testcase, haven't tried to bootstrap/regtest it nor have any
idea whether some IRA bookkeeping will need to be updated in that case.

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-08 15:51:18 UTC ---
Author: jakub
Date: Tue Mar  8 15:51:12 2011
New Revision: 170780

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=170780
Log:
    PR debug/47881
    * ira.c (ira): Call df_analyze again if delete_trivially_dead_insns
    removed anything.

    * gcc.dg/pr47881.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/pr47881.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/cp/ChangeLog
    trunk/gcc/ira.c
    trunk/gcc/testsuite/ChangeLog

[Bug debug/47881] [4.6 Regression] -fcompare-debug failure (length) with -O -fno-dce -funroll-loops -fno-web

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47881

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-08 15:54:57 UTC ---
Fixed.