[Bug rtl-optimization/35542] New: fwprop only propagates one operand

[Bug rtl-optimization/35542] New: fwprop only propagates one operand

[hutchinsonandy at aim dot com]

fwprop.c  currently has a bug where a successful  propagation to one operand 
of an instruction will prevent propagation to any remaining operands.


The cause is due to the use of loc_mentioned_in_p() to check that a reference,
provided by earlier DF scan, still exist in an instruction.

The test is intended to check that an earlier propagation and simplification 
has not removed D/U references.

However, loc_mentioned_in_p(), compares addresses of rtx to determine 
equivalence. If an instruction has already been modified and simplified, this
will
longer apply - even if the def/use is still valid.

This problem was already noted in Nov, but no bug report seems to have been 
filed.

http://gcc.gnu.org/ml/gcc-patches/2007-11/msg00170.html


I will attach patch, that uses reg_mentioned_p() as a substitute. The only
differences I noted where:

a) reg_mentioned_p() does not match physical sub registers of longer hard
registers.
This seems to have no consequence since fwprop entirely rejects hard_registers 
 in latter code. Perhaps for clarity, hard registers could be ignored earlier.

b) registers in asm_operands are found. Which seems beneficial if they are
pseudos and again ignored if they are hard registers.


I am only able to test this with AVR port. In that it was 100% successful with
no 
regressions of torture/execute testsuite.


-- 
           Summary: fwprop only propagates one operand
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hutchinsonandy at aim dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] fwprop only propagates one operand

[hutchinsonandy at aim dot com]

------- Comment #1 from hutchinsonandy at aim dot com  2008-03-11 20:34 -------
Created an attachment (id=15300)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15300&action=view)
Patch to search modified instruction for register.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] fwprop only propagates one operand

[bonzini at gcc dot gnu dot org]

------- Comment #2 from bonzini at gnu dot org  2008-04-02 09:57 -------
Subject: Bug 35542

Author: bonzini
Date: Wed Apr  2 09:56:17 2008
New Revision: 133829

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133829
Log:
2008-04-02  Andy Hutchinson <hutchinsonamdy@aim.com>

        PR rtl-optimization/35542
        * fwprop.c (forward_propagate_and_simplify): Replace
        loc_reg_mentioned_in_p with reg_mentioned_p.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/fwprop.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[bonzini at gnu dot org]

------- Comment #3 from bonzini at gnu dot org  2008-04-02 09:57 -------
committed to trunk, will backport to 4.3 in due time (causes regressions for
AVR)


-- 

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
      Known to fail|                            |4.3.0
      Known to work|                            |4.4.0
   Last reconfirmed|0000-00-00 00:00:00         |2008-04-02 09:57:10
               date|                            |
            Summary|fwprop only propagates one  |[4.3 Regression] fwprop only
                   |operand                     |propagates one operand


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[eric dot weddington at atmel dot com]

------- Comment #4 from eric dot weddington at atmel dot com  2008-04-02 15:21 -------
(In reply to comment #3)
> committed to trunk, will backport to 4.3 in due time (causes regressions for
> AVR)
> 

Could you list what fails?
Thanks!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[bonzini at gnu dot org]

------- Comment #5 from bonzini at gnu dot org  2008-04-02 15:25 -------
I meant that this is a patch that is scheduled for backporting to 4.3, because
it fixes regressions on AVR.

The text between parentheses should have been "bug causes regressions for AVR".
 Sorry.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[hutchinsonandy at aim dot com]

------- Comment #6 from hutchinsonandy at aim dot com  2008-04-02 15:44 -------
Subject: Re:  [4.3 Regression] fwprop only propagates
 one operand

Eric,

it's difficult to give you a specfic example as the propagation is very 
sensitive to generated code. I found this looking at other AVR bugs and 
discovered it was not working. (I'll  look up that example latter for 
you).

It not an obvious thing as other (good) changes due to DF merge, 
re-arrange code enough to obscure the omission. But the result is an 
extra move or redundant instruction here and there.

(its also not at all specfic to AVR)

Andy





-----Original Message-----
From: eric dot weddington at atmel dot com <gcc-bugzilla@gcc.gnu.org>
To: hutchinsonandy@aim.com
Sent: Wed, 2 Apr 2008 10:21 am
Subject: [Bug rtl-optimization/35542] [4.3 Regression] fwprop only 
propagates one operand




------- Comment #4 from eric dot weddington at atmel dot com  
2008-04-02 15:21
-------
(In reply to comment #3)
> committed to trunk, will backport to 4.3 in due time (causes 
regressions for
> AVR)
>

Could you list what fails?
Thanks!


--


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[aoliva at gcc dot gnu dot org]

------- Comment #7 from aoliva at gcc dot gnu dot org  2008-04-29 08:19 -------
Subject: Bug 35542

Author: aoliva
Date: Tue Apr 29 08:18:36 2008
New Revision: 134782

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=134782
Log:
* fwprop.c (forward_propagate_and_simplify): Replace entire
var location rtx.  Revert part of 2007-11-08 obviated by:
2008-04-02  Andy Hutchinson <hutchinsonamdy@aim.com>
PR rtl-optimization/35542
* fwprop.c (forward_propagate_and_simplify): Replace
loc_reg_mentioned_in_p with reg_mentioned_p.

Modified:
    branches/var-tracking-assignments-branch/gcc/ChangeLog.vta
    branches/var-tracking-assignments-branch/gcc/fwprop.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.3.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[bonzini at gnu dot org]

------- Comment #8 from bonzini at gnu dot org  2008-08-01 09:54 -------
backported


-- 

bonzini at gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|4.4.0                       |4.4.0 4.3.2
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542

[Bug rtl-optimization/35542] [4.3 Regression] fwprop only propagates one operand

[bonzini at gcc dot gnu dot org]

------- Comment #9 from bonzini at gnu dot org  2008-08-01 09:55 -------
Subject: Bug 35542

Author: bonzini
Date: Fri Aug  1 09:54:04 2008
New Revision: 138505

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=138505
Log:
2008-08-01  Paolo Bonzini  <bonzini@gnu.org>

        Backport from mainline:
        2008-04-02  Andy Hutchinson <hutchinsonamdy@aim.com>

        PR rtl-optimization/35542
        * fwprop.c (forward_propagate_and_simplify): Replace
        loc_reg_mentioned_in_p with reg_mentioned_p.


Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/fwprop.c


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542