Sender: yakush AT ipmnet DOT ru
Message-ID: <36D64959.8BB95024@ipmnet.ru>
Date: Fri, 26 Feb 1999 10:12:25 +0300
From: "S.Yakush" <yakush AT ipmnet DOT ru>
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To: pgcc AT delorie DOT com
Subject: PGCC Optimization bug (?)
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Reply-To: pgcc AT delorie DOT com

Hi there,

I came across an optimisation-related bug in
pgcc-1.1.1 :-(
The program below has been distilled from my code
in which I use 1D double array to store 2D data,
the Var class allocates the memory and provides
an access function Var::Arr. This program works
fine when compiled by egcs-1.1.1 with or without
optimisation. However, pgcc-1.1.1
(bootstrapped with --enable-haifa --enable-threads
--enable-shared) gives a weird result: the unoptimised
code runs fine, but optimised (-O1, -O2, -O3) one
crashes when data element a->Arr(2,2) is accessed.
At the same time, a->Arr(0,2) can be accessed with
any optimisation. If the result is assigned to a
local variable (rather than the global one),
the code runs as well.

Here is the program tst.C:

//------------------------------------- start
class Var{
public:
    double* Array;
    int NX;
    int NY;
    Var(int Nx, int Ny){
 NX = Nx; NY = Ny;
 Array = new double[NX*NY];
 for(register int i = 0; i < NX*NY; i++)
     Array[i] = (double)i; // Initialise somehow, just in case
    }
    double Arr(int i, int j){return (*(Array+i+NX*j));} // Access
function
};

double V;
int main()
{

  Var *a = new Var(5,5);
//  Uncomment one line of the following three:
//             V = a->Arr(0,2); // This works fine (V is global)
//      double V = a->Arr(2,2); // This works fine (V is local)
               V = a->Arr(2,2); // This causes Segmentation fault
  return 0;
}
//-------------------------------------- end

An here is what happens:

$g++ -v -O3 tst.C -o tst
Reading specs from
/usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/specs
gcc version pgcc-2.91.60 19981201 (egcs-1.1.1 release)
 /usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/cpp
-lang-c++ -v -undef -D__GNUC__=2 -D__GNUG__=2 -D__cplusplus
-D__GNUC_MINOR__=91 -D__ELF__ -Dunix -Di386 -D__i386__ -Dlinux -D__ELF__
-D__unix__ -D__i386__ -D__i386__ -D__linux__ -D__uni
x -D__i386 -D__linux -Asystem(posix) -D__EXCEPTIONS -D__OPTIMIZE__
-Asystem(unix) -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__
-Di686 -Dpentiumpro -D__i686 -D__i686__ -D__pentiumpro -D__pentiumpro__
tst.C /tmp/ccphIXyQ.ii
GNU CPP version pgcc-2.91.60 19981201 (egcs-1.1.1 release) (i386
Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/pgcc-1.1.1/include/g++
 /usr/local/include
 /usr/local/pgcc-1.1.1/i686-pc-linux-gnu/include
 /usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/include

 /usr/include
End of search list.
 /usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/cc1plus
/tmp/ccphIXyQ.ii -quiet -dumpbase tst.cc -O3 -version -o /tmp/ccOZ6PAy.s

GNU C++ version pgcc-2.91.60 19981201 (egcs-1.1.1 release)
(i686-pc-linux-gnu) compiled by GNU C version pgcc-2.91.60 19981201
(egcs-1.1.1 release).
 as -V -Qy -o /tmp/ccd88pOi.o /tmp/ccOZ6PAy.s
GNU assembler version 2.9.1 (i686-pc-linux-gnu), using BFD version
2.9.1.0.15
 /usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/collect2
-m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o tst /usr/lib/crt1.o
/usr/lib/crti.o
/usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/crtbegin.o
-L/usr/local/pgcc-
1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60
-L/usr/local/pgcc-1.1.1/i686-pc-linux-gnu/lib
-L/usr/local/pgcc-1.1.1/lib /tmp/ccd88pOi.o -lstdc++ -lm -lgcc -lc -lgcc
/usr/local/pgcc-1.1.1/lib/gcc-lib/i686-pc-linux-gnu/pgcc-2.91.60/crtend.o
/usr/lib/crtn
.o
$
$./tst
Segmentation fault (core dumped)
$

Another hint: if NX in the access function Arr(i,j)
is substituted manually by a constant 5, everything
works fine even with optimisation.

Thanks
S.Yakush