[Bug rtl-optimization/57676] New: ICE: Maximum number of LRA constraint passes is achieved (30)

[Bug rtl-optimization/57676] New: ICE: Maximum number of LRA constraint passes is achieved (30)

[antoine.balestrat at gmail dot com]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

            Bug ID: 57676
           Summary: ICE: Maximum number of LRA constraint passes is
                    achieved (30)
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoine.balestrat at gmail dot com

Using GCC 4.9.0 as of 20130622 :

$ cat lra.c
int a, b, c;

void f(p1)
{
    for(;;)
    {
        if(p1 ? : (c /= 0))
        {
            int d;

            for(; d; d++)
            {
                for(b = 0; b < 4; b++)
                    p1 /= p1;
lbl:
                while(a);
            }
        }

        if((c &= 1))
            goto lbl;
    }
}

$ xgcc -w -O2 -funroll-loops lra.c
lra.c: In function ‘f’:
lra.c:23:1: internal compiler error: Maximum number of LRA constraint passes is
achieved (30)

 }
 ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
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From: "schlaffi at users dot sourceforge.net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/57674] wrong distribution for  std::binomial_distribution::operator()(g,param)
Date: Sat, 22 Jun 2013 16:40:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW674

--- Comment #2 from schlaffi at users dot sourceforge.net ---
Created attachment 30338
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id0338&actioníit
corrected version of the example file

sorry, forgot one line, the output should be

distribution 1: p = 0.8, f = 0.798828
distribution 2: p = 0.3, f = 0.206055

(bad) vs.

distribution 1: p = 0.8, f = 0.793945
distribution 2: p = 0.3, f = 0.308594

(good)

[Bug rtl-optimization/57676] [4.8/4.9 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-*-*, i?86-*-*
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |ra
   Last reconfirmed|                            |2013-06-24
                 CC|                            |vmakarov at gcc dot gnu.org
     Ever confirmed|0                           |1
            Summary|ICE: Maximum number of LRA  |[4.8/4.9 Regression] ICE:
                   |constraint passes is        |Maximum number of LRA
                   |achieved (30)               |constraint passes is
                   |                            |achieved (30)
   Target Milestone|---                         |4.8.2

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug rtl-optimization/57676] [4.8/4.9 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[vmakarov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

--- Comment #2 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
That is a pretty interesting test case.  Roughly speaking, we have chains of
divmodsi4 insns:

p1 / p2
...
p3 / p1

P1 (and many others) gets AX.  But it is necessary for P3 in the second insn. 
So on each LRA pass, there is a generation of reloads for one pseudo as P1. 
For these test case, LRA needs 36 passes (on each pass only 2 insns are
processed).  The current max number of passes is 30.

The simplest solution is to increase the max number of passes (and I probably
do it as the first solution).  But it is not the best solution as we don't know
how long the insn chain can be.  We need something smarter but currently I have
no ideas how to do it for any length of such insn chain.

[Bug rtl-optimization/57676] [4.8/4.9 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.2                       |4.8.3

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.2 has been released.

[Bug rtl-optimization/57676] [4.8/4.9 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

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

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I wonder if there is an algorithm to fall back to that doesn't require
iteration.
Or, if not, if we can instead check if there was progress during the last
iteration (interpreting the limit as a way to check whether we'll iterate
indefinitely).

[Bug rtl-optimization/57676] [4.8/4.9/4.10 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.3                       |4.8.4

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 4.8.3 is being released, adjusting target milestone.

[Bug rtl-optimization/57676] [4.8/4.9/5 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.4                       |4.8.5

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.4 has been released.

[Bug rtl-optimization/57676] [4.8/4.9/5/6 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.5                       |4.9.3

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
The gcc-4_8-branch is being closed, re-targeting regressions to 4.9.3.

[Bug rtl-optimization/57676] [4.9/5/6 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.3 has been released.

[Bug rtl-optimization/57676] [4.9/5/6 Regression] ICE: Maximum number of LRA constraint passes is achieved (30)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57676

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.3                       |4.9.4