[Bug middle-end/37674] New: Bootstrap failure due to miscompilation of genattrtab

[Bug middle-end/37674] New: Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

With the patch for PR37535 applied to mainline GCC the bootstrap still fails
due to a miscompilation.  The problem is that r52 is assigned to r6 what
collides with an INSN loading r6 with a parameter for a CALL.

I think the problem is created in ira_flattening.  Allocno a3 is a parent of
a87. For a87 the conflict with r6 is properly recorded. Afterwards ira_flatting
merges a87 into a3 without propagating the conflict_hard_regs set. So the
conflict with r6 is lost and ira_reassign_pseudos later on assigns r52 to hard
reg r6. 

There is already code in ira_flattening which propagates the conflict sets. But
the code is only enabled if propagate_p is true. This in turn seems only to get
set if the loop once merged allocnos with different regnos?! I unfortunately
don't understand this enough to come up with a patch. So I better leave that to
you :)  Please contact me if you need more information.

I wasn't able to reduce the testcase (genattrtab) since it is quite difficult
to see from the code if the miscompile occurred or not.

;; a3(r52,l0) conflicts: a1(r87,l0) ......
;;     total conflict hard regs: 0-6 14
;;     conflict hard regs: 0-5 14

;; a87(r52,l2) conflicts: a86(r48,l2) .....
;;     total conflict hard regs: 0-6 14
;;     conflict hard regs: 0-6 14

...
Moving ranges of a87r52 to a3r52:  [245..248] [234..243] [229..232] [218..227]
[173..189] [126..169]

...
 Try assign 52(a3), cost=268: reassign to 6


-- 
           Summary: Bootstrap failure due to miscompilation of genattrtab
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: krebbel at gcc dot gnu dot org
 GCC build triplet: s390x-ibm-linux
  GCC host triplet: s390x-ibm-linux
GCC target triplet: s390x-ibm-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

-- 

krebbel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

------- Comment #1 from krebbel at gcc dot gnu dot org  2008-09-30 15:30 -------
The failure can currently be seen bootstrapping ira-merge branch (rev.:
140776).

configure --enable-shared --with-system-zlib --enable-threads=posix
--enable-__cxa_atexit --enable-checking --enable-decimal-float
--enable-languages=c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Keywords|                            |ra, wrong-code
            Summary|Bootstrap failure due to    |[4.4 Regression] Bootstrap
                   |miscompilation of genattrtab|failure due to
                   |                            |miscompilation of genattrtab
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

------- Comment #2 from krebbel at gcc dot gnu dot org  2008-10-06 14:07 -------
Just to check whether the propagation of the conflicting hard regs in
ira_flatting really is the main problem I've tried the following patch. With
that patch the ira branch bootstraps on s390x.

Index: gcc/ira-build.c
===================================================================
--- gcc/ira-build.c.orig        2008-10-06 11:16:39.000000000 +0200
+++ gcc/ira-build.c     2008-10-06 14:44:57.000000000 +0200
@@ -2147,7 +2147,7 @@ ira_flattening (int max_regno_before_emi
          ira_assert (ALLOCNO_CAP_MEMBER (parent_a) == NULL);
          if (ALLOCNO_MEM_OPTIMIZED_DEST (a) != NULL)
            mem_dest_p = true;
-         if (propagate_p)
+         /*      if (propagate_p)*/
            {
              if (!allocno_propagated_p [ALLOCNO_NUM (parent_a)])
                COPY_HARD_REG_SET (ALLOCNO_TOTAL_CONFLICT_HARD_REGS (parent_a),

I think one reason why this problem does not occur more often and not on other
targets is that on S/390 r6 is used as argument register but is also call
saved!

The conflict between r52 and hard reg r6 is recorded for an instruction which
loads the argument for a function call. Since such an INSN is most likely more
or less directly followed by a call instruction the missing propagation of
conflicting hard regs is papered over by ira_build_conflicts. This function
always adds the call clobbered registers to the conflict sets of pseudos which
are live across function calls. For r6 on S/390 this does not happen what - at
least to my understanding - reveals the bug in ira_flattening.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

------- Comment #3 from krebbel at gcc dot gnu dot org  2008-10-10 16:56 -------
Vladimir could you please have a look. Mainline is still not bootstrapping on
S/390 due to this problem.


-- 

krebbel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |vmakarov at gcc dot gnu dot
                   |dot org                     |org
           Severity|critical                    |blocker


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[vmakarov at redhat dot com]

------- Comment #4 from vmakarov at redhat dot com  2008-10-10 20:16 -------
I am sorry that I was silent.  I am working on this.  Please don't worry,
Andreas. Simply I have a lot of IRA bugs.  I hope the problem will be solved on
next week.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[vmakarov at redhat dot com]

------- Comment #5 from vmakarov at redhat dot com  2008-10-14 19:50 -------
Updating of total_conflict_hard_regs in ira-build.c::ira_flattening was
completely wrong.  So I rewrite the calculation of total_conflict_hard_regs and
total_no_stack_reg_p.  It is now done from the scratch.  The code became more
readable and there is no visible slowdown of IRA.

I'll send a patch solving the PR later today.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[hjl at gcc dot gnu dot org]

------- Comment #6 from hjl at gcc dot gnu dot org  2008-10-14 22:50 -------
Subject: Bug 37674

Author: hjl
Date: Tue Oct 14 22:49:36 2008
New Revision: 141122

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=141122
Log:
2008-10-14  Vladimir Makarov  <vmakarov@redhat.com>

        PR middle-end/37674
        * ira-build.c (ira_flattening): Recalculate
        ALLOCNO_TOTAL_NO_STACK_REG_P and ALLOCNO_TOTAL_CONFLICT_HARD_REGS
        from the scratch instead of the propagation.

Modified:
    branches/ira-merge/gcc/ChangeLog.ira
    branches/ira-merge/gcc/ira-build.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[vmakarov at gcc dot gnu dot org]

------- Comment #7 from vmakarov at gcc dot gnu dot org  2008-10-16 00:23 -------
Subject: Bug 37674

Author: vmakarov
Date: Thu Oct 16 00:22:13 2008
New Revision: 141159

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=141159
Log:
2008-10-15  Vladimir Makarov  <vmakarov@redhat.com>

        PR middle-end/37674
        * ira-build.c (ira_flattening): Recalculate
        ALLOCNO_TOTAL_NO_STACK_REG_P and ALLOCNO_TOTAL_CONFLICT_HARD_REGS
        from the scratch instead of the propagation.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/ira-build.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2008-10-20 11:46 -------
Does s390x-linux bootstrap now (possibly with PR37815 fix as well)?  Can this
be closed?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

------- Comment #9 from krebbel at gcc dot gnu dot org  2008-10-20 12:07 -------
(In reply to comment #8)
> Does s390x-linux bootstrap now (possibly with PR37815 fix as well)?  Can this
> be closed?

This particular problem seems to be fixed for s390x. GCC still doesn't
bootstrap - even with the patch from PR37815. There still is a problem with
value range propagation. I'm working on this.


-- 

krebbel at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674

[Bug middle-end/37674] [4.4 Regression] Bootstrap failure due to miscompilation of genattrtab

[krebbel at gcc dot gnu dot org]

------- Comment #10 from krebbel at gcc dot gnu dot org  2008-10-20 12:08 -------
My testcase works fine with current GCC mainline.


-- 

krebbel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |VERIFIED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37674