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From: "ishiura-compiler at ml dot kwansei.ac.jp" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/57131] New: Wong register assignment?
Date: Wed, 01 May 2013 06:02:00 -0000
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X-Bugzilla-Component: rtl-optimization
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X-Bugzilla-Who: ishiura-compiler at ml dot kwansei.ac.jp
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57131

             Bug #: 57131
           Summary: Wong register assignment?
    Classification: Unclassified
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ishiura-compiler@ml.kwansei.ac.jp


This miscompile occurs only on 32bit x86 (i686) target of GCC 4.8.1
(prerelease).  
(There is no problem with x86_64 target or GCC 4.7.3.) 
A dubious option is "-foptimize-register-move."

  $ cat error.c

  int main (void)
  {
    volatile int x1 = 0;
    volatile long long x2 = 0;
    volatile int x3 = 0;
    volatile int x4 = 1;
    volatile int x5 = 1;
    volatile long long x6 = 1;

    long long t = ( ( x1 * ( x2 << x3 ) ) / (x4 * x5) ) + x6 ;

    return (t == 1); 
  }

  $ i686-pc-linux-gnu-gcc-4.8.1 error.c -O1 -fexpensive-optimizations
-foptimize-register-move
  $ ./a.out
  Floating point exception (core dumped)

-----

$ i686-pc-linux-gnu-gcc-4.8.1 -v
Using built-in specs.
COLLECT_GCC=i686-pc-linux-gnu-gcc-4.8.1
COLLECT_LTO_WRAPPER=/usr/local/i686-tools/gcc-4.8.1/libexec/gcc/i686-pc-linux-gnu/4.8.1/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: /home/hassy-i686-linux/gcc/configure
--prefix=/usr/local/i686-tools/gcc-4.8.1/
--with-gmp=/usr/local/gmp-5.1.1/ --with-mpfr=/usr/local/mpfr-3.1.2/
--with-mpc=/usr/local/mpc-1.0.1/ --disable-multilib --disable-nls
--enable-languages=c
Thread model: posix
gcc version 4.8.1 20130428 (prerelease) (GCC)