[Bug rtl-optimization/30931] New: Simple test case loops infinitely with -O1 -fstrength-reduce.

[Bug rtl-optimization/30931] New: Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

The simple test which I'll attach shortly, loops infinitely when compiled with
-O1 -fstrength-reduce and executes fine with plain -O1.  Doing a little
debugging, it seems the loop index variable "i" is not incremented within the
loop causing us to loop forever.

I have tested this using the latest FSF 4.1, 4.2 and mainline compiler sources
and it only fails using the 4.1 compiler.  Using an older 3.4.6 distro
compiler, it executes fine, so this _looks_ like a regression.


-- 
           Summary: Simple test case loops infinitely with -O1 -fstrength-
                    reduce.
           Product: gcc
           Version: 4.1.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bergner at gcc dot gnu dot org
 GCC build triplet: i686-linux
  GCC host triplet: i686-linux
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

------- Comment #1 from bergner at gcc dot gnu dot org  2007-02-22 22:40 -------
Created an attachment (id=13092)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13092&action=view)
Reduced testcase showing the infinite looping


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[steven at gcc dot gnu dot org]

------- Comment #2 from steven at gcc dot gnu dot org  2007-02-22 23:26 -------
I cannot reproduce this.
Please paste the output of gcc -v.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-02-22 23:29 -------
> it only fails using the 4.1 compiler.

Well that is because loop.c has been removed in 4.2 and above.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

------- Comment #4 from bergner at gcc dot gnu dot org  2007-02-22 23:32 -------
This is using source checked out this afternoon (revision 122219):

bg47:bergner% ./install/gcc-4.1/bin/gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../../gcc-4_1-20070222/configure --enable-shared
--enable-threads=posix --enable-checking --enable-languages=c
--prefix=/tmp/bergner/install/gcc-4.1
Thread model: posix
gcc version 4.1.3 20070222 (prerelease)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-02-23 10:03 -------
Works for me.  Can you tell us all options in effect?  I.e. gcc -O
-fstrength-reduce t.c -v output?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

------- Comment #6 from bergner at gcc dot gnu dot org  2007-02-23 14:06 -------
Here's the output you asked for using the latest 4.1 sources I built yesterday.
This also fails for me using the system compilers on Ubuntu Edgy and SLES10.
I'll try and track down a x86 RHEL5 system to test there too.

Please note it's not the compiler that is looping forever, but the built binary
when executed.

bg47:bergner% ./install/gcc-4.1/bin/gcc -O1 -fstrength-reduce pr30311.c -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../../gcc-4_1-20070222/configure --enable-shared
--enable-threads=posix --enable-checking --enable-languages=c
--prefix=/tmp/bergner/install/gcc-4.1
Thread model: posix
gcc version 4.1.3 20070222 (prerelease)
 /tmp/bergner/install/gcc-4.1/libexec/gcc/i686-pc-linux-gnu/4.1.3/cc1 -quiet -v
pr30311.c -quiet -dumpbase pr30311.c -mtune=pentiumpro -auxbase pr30311 -O1
-version -fstrength-reduce -o /tmp/cc6Cx7Y6.s
ignoring nonexistent directory
"/tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /tmp/bergner/install/gcc-4.1/include
 /tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3/include
 /usr/include
End of search list.
GNU C version 4.1.3 20070222 (prerelease) (i686-pc-linux-gnu)
        compiled by GNU C version 3.4.4 20050721 (Red Hat 3.4.4-2).
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 3c763771770d7626aeca3ba678fea9f5
 as -V -Qy -o /tmp/ccmkRFA6.o /tmp/cc6Cx7Y6.s
GNU assembler version 2.15.92.0.2 (i386-redhat-linux) using BFD version
2.15.92.0.2 20040927
 /tmp/bergner/install/gcc-4.1/libexec/gcc/i686-pc-linux-gnu/4.1.3/collect2
--eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o
/usr/lib/crti.o
/tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3/crtbegin.o
-L/tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3
-L/tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3/../../..
/tmp/ccmkRFA6.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed
-lgcc_s --no-as-needed
/tmp/bergner/install/gcc-4.1/lib/gcc/i686-pc-linux-gnu/4.1.3/crtend.o
/usr/lib/crtn.o


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2007-02-23 14:13 -------
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|i686-linux                  |
   GCC host triplet|i686-linux                  |
 GCC target triplet|i686-linux                  |i?86-*-*
           Keywords|                            |wrong-code
      Known to fail|                            |4.0.0 4.0.4 4.1.0 4.1.2
      Known to work|                            |3.4.6 4.2.0
   Last reconfirmed|0000-00-00 00:00:00         |2007-02-23 14:13:03
               date|                            |
            Summary|Simple test case loops      |[4.1 Regression] Simple test
                   |infinitely with -O1 -       |case loops infinitely with -
                   |fstrength-reduce.           |O1 -fstrength-reduce.


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

------- Comment #8 from bergner at gcc dot gnu dot org  2007-02-23 14:17 -------
Created an attachment (id=13097)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13097&action=view)
Good assembly output from the 4.1 compiler (-O1 -fno-strength-reduce)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bergner at gcc dot gnu dot org]

------- Comment #9 from bergner at gcc dot gnu dot org  2007-02-23 14:17 -------
Created an attachment (id=13098)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13098&action=view)
Bad assembly output from the 4.1 compiler (-O1 -fstrength-reduce)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bonzini at gnu dot org]

------- Comment #10 from bonzini at gnu dot org  2007-02-23 14:30 -------
No, i (which is in %edx) *is* being incremented.  It's the strength-reduced
derived induction variable that is constructed in a wrong way.  The optimized
code looks like:

void bug (struct s *p)
{
  int i;
  struct s *pp = p;
  for (i=0; i < 2; i++)
    {
      goto loop_cond;

     loop:
      /* ??? I think gcc assumes that pp (%eax) is an induction variable of
         the inner loop... */
      pp[-1].first = 0;
     loop_cond:
      if (!pp[0].first)
        goto break_out_of_inner_loop;
      if (pp[0].done)
        goto loop;

     break_out_of_inner_loop;
      pp++; /* actually adds sizeof (struct s) in the asm code */
      i++;
    }
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[bonzini at gnu dot org]

------- Comment #11 from bonzini at gnu dot org  2007-02-23 14:32 -------
>   for (i=0; i < 2; i++)

Well, that's obviously

    for (i=0; i < 2; )

in my code of comment #10.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 Regression] Simple test case loops infinitely with -O1 -fstrength-reduce.

[ebotcazou at gcc dot gnu dot org]

------- Comment #12 from ebotcazou at gcc dot gnu dot org  2007-02-26 19:18 -------
Investigating.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |ebotcazou at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-02-23 14:13:03         |2007-02-26 19:18:18
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 regression] infinite loop with -O1 -fstrength-reduce

[ebotcazou at gcc dot gnu dot org]

------- Comment #13 from ebotcazou at gcc dot gnu dot org  2007-02-27 20:21 -------
Subject: Bug 30931

Author: ebotcazou
Date: Tue Feb 27 20:21:17 2007
New Revision: 122383

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=122383
Log:
        PR rtl-optimization/30931
        * loop.c (combine_givs_p): Return false if either GIV is not
        always executed.


Added:
    branches/gcc-4_1-branch/gcc/testsuite/gcc.c-torture/execute/20070227-1.c
Modified:
    branches/gcc-4_1-branch/gcc/ChangeLog
    branches/gcc-4_1-branch/gcc/loop.c
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931

[Bug rtl-optimization/30931] [4.1 regression] infinite loop with -O1 -fstrength-reduce

[ebotcazou at gcc dot gnu dot org]

------- Comment #14 from ebotcazou at gcc dot gnu dot org  2007-02-27 20:23 -------
Fixed on 4.1 branch.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2007-
                   |                            |02/msg02159.html
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30931