[Bug c/49207] New: Instruction scheduling error in GCC mips cross-compiler

[Bug c/49207] New: Instruction scheduling error in GCC mips cross-compiler

[hanib at ece dot ubc.ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

           Summary: Instruction scheduling error in GCC mips
                    cross-compiler
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hanib@ece.ubc.ca


When compiling a testbench program using -O2 optimization, the GCC MIPS
cross-compiler generates an incorrect instruction sequence (a store before a
load to the same memory location) which leads to a memory corruption problem
and crashes the program. If the -O1 or -O0 switches are used, this problem does
not occur.

The output of the gcc -v -save-temps command is included below and the test.i
file is attached. I am also including, below, the portion of assembly code that
contains the erroneous instruction sequence (see arrows).

/mnt/disk/home/tools/mipsel/bin/mipsel-linux-gcc   -v -save-temps -O2 -static  
-DSPEC_CPU_LINUX_IA32       test.o             -lm        -o perlbench
Using built-in specs.
Target: mipsel-linux
Configured with: ../../src/gcc-4.4.3/configure --target=mipsel-linux
--prefix=/mnt/disk/home/tools/mipsel --with-sysroot=/mnt/disk/home/tools/mipsel
--disable-libssp --disable-libgomp --disable-libmudflap --disable-nls
--enable-languages=c,c++,fortran
Thread model: posix
gcc version 4.4.3 (GCC) 
COMPILER_PATH=/mnt/disk/home/tools/mipsel/libexec/gcc/mipsel-linux/4.4.3/:/mnt/disk/home/tools/mipsel/libexec/gcc/mipsel-linux/4.4.3/:/mnt/disk/home/tools/mipsel/libexec/gcc/mipsel-linux/:/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/:/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/:/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/../../../../mipsel-linux/bin/
LIBRARY_PATH=/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/:/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/../../../../mipsel-linux/lib/:/mnt/disk/home/tools/mipsel/lib/:/mnt/disk/home/tools/mipsel/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-static' '-DSPEC_CPU_LINUX_IA32'
'-o' 'perlbench' '-mllsc' '-mno-shared'
 /mnt/disk/home/tools/mipsel/libexec/gcc/mipsel-linux/4.4.3/collect2
--sysroot=/mnt/disk/home/tools/mipsel -EL -static -o perlbench
/mnt/disk/home/tools/mipsel/usr/lib/crt1.o
/mnt/disk/home/tools/mipsel/usr/lib/crti.o
/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/crtbeginT.o
-L/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3
-L/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/../../../../mipsel-linux/lib
-L/mnt/disk/home/tools/mipsel/lib -L/mnt/disk/home/tools/mipsel/usr/lib test.o
-lm --start-group -lgcc -lgcc_eh -lc --end-group
/mnt/disk/home/tools/mipsel/lib/gcc/mipsel-linux/4.4.3/crtend.o
/mnt/disk/home/tools/mipsel/usr/lib/crtn.o
/mnt/disk/home/tools/mipsel/usr/lib/crt1.o: In function `__start':

>>>>>>>>>>>>>>>>>>>>>>> assembly code >>>>>>>>>>>>>>>>>>>>

$L100:
    lw    $3,%got(PL_xiv_root)($28)
    lw    $2,0($16)
    lw    $5,0($3)
    addiu    $4,$2,12
>>>>	sw	$5,12($2)
>>>>	lw	$19,12($2)
    li    $2,2            # 0x2
    beq    $17,$2,$L184
    sw    $4,0($3)

    beq    $18,$0,$L111
    nop

    move    $20,$0
    move    $21,$0
    move    $18,$0

[Bug c/49207] Instruction scheduling error in GCC mips cross-compiler

[hanib at ece dot ubc.ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

--- Comment #1 from hanib at ece dot ubc.ca 2011-05-28 06:19:34 UTC ---
Created attachment 24384
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24384
preprocessed file

[Bug c/49207] Instruction scheduling error in GCC mips cross-compiler

[hanib at ece dot ubc.ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

--- Comment #2 from hanib at ece dot ubc.ca 2011-05-28 06:20:36 UTC ---
Created attachment 24385
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24385
assembly language file

[Bug c/49207] Instruction scheduling error in GCC mips cross-compiler

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-05-28 09:32:38 UTC ---
I think you have an aliasing problem in your code.

[Bug c/49207] Instruction scheduling error in GCC mips cross-compiler

[hanib at ece dot ubc.ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

--- Comment #4 from hanib at ece dot ubc.ca 2011-05-28 21:21:40 UTC ---
(In reply to comment #3)
> I think you have an aliasing problem in your code.

The code I am compiling is the Perlbench benchmark from SPEC-CPU2006. If I
compile the code for an Intel machine using -O2 there is no problem. This
problem only appears when I use the GCC MIPS cross-compiler with the -O2
switch. I also traced through the code and the sequence of these two
instructions should be reversed.

[Bug middle-end/49207] Instruction scheduling error in GCC mips cross-compiler

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49207

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
          Component|c                           |middle-end
         Resolution|---                         |INVALID

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to hanib from comment #4)
> (In reply to comment #3)
> > I think you have an aliasing problem in your code.
> 
> The code I am compiling is the Perlbench benchmark from SPEC-CPU2006. If I
> compile the code for an Intel machine using -O2 there is no problem. This
> problem only appears when I use the GCC MIPS cross-compiler with the -O2
> switch. I also traced through the code and the sequence of these two
> instructions should be reversed.

Perl in SPEC CPU 2006 has known aliasing bugs in it; just use
-fno-strict-aliasing.