Dear GCC folks:
I'm having a problem with GCC 2.95.3 that appears to be a compiler bug. It
seems to be optimizing out inlined function code with side effects, and is
related to binding a non-const pointer to a const pointer reference function
parameter. The problem only happens with optimization on, and goes away with
-O0.
I assume this must be known problem, but I'm having a hard time finding a patch
to fix it. It is not an option at this time to upgrade to a newer compiler
version, but we are planning to do that in the future.
Below is the test program and output.
I really appreciate any help you can give.
Thanks in advance,
--Ray
-----------------------
#include <iostream>
#include <iomanip>
#include <string.h>
typedef unsigned char byte;
inline unsigned unpack2 (const byte *&data)
{
unsigned val = data[0] << 8 | data[1];
data += 2;
return val;
}
inline unsigned unpack2 (const byte *&data, unsigned &count)
{
unsigned val = data[0] << 8 | data[1];
data += 2;
count -= 2;
return val;
}
/*
inline unsigned unpack2 (byte *&data)
{
unsigned val = data[0] << 8 | data[1];
data += 2;
return val;
}
inline unsigned unpack2 (byte *&data, unsigned &count)
{
unsigned val = data[0] << 8 | data[1];
data += 2;
count -= 2;
return val;
}
*/
void extractInfo (byte *&data, unsigned &datalen,
unsigned &f1, unsigned &f2)
{
cout << "data = " << data << ", datalen = " << datalen << endl;
f1 = unpack2 (data, datalen);
cout << "data = " << data << ", datalen = " << datalen << endl;
byte *peek = data;
//const byte *peek = data; // **** Adding "const" works around the
compiler problem ****
// Another work-around is to uncomment the
non-const f1 of unpack2() above
unsigned tmp = datalen;
cout << "peek = " << peek << ", tmp = " << tmp << endl;
(void) unpack2 (peek, tmp); // skip over irrelevant field
cout << "peek = " << peek << ", tmp = " << tmp << endl;
(void) unpack2 (peek, tmp); // skip over irrelevant field
cout << "peek = " << peek << ", tmp = " << tmp << endl;
unsigned xlen = unpack2 (peek, tmp);
cout << "peek = " << peek << ", tmp = " << tmp << endl;
f2 = xlen;
}
int
main(int, char**)
{
byte *x = "0123456789";
unsigned len = strlen(x);
unsigned fld1, fld2;
extractInfo (x, len, fld1, fld2);
cout << "x = " << x << endl;
cout << "len = " << len << endl;
cout << "fld1 = " << hex << fld1 << dec << endl;
cout << "fld2 = " << hex << fld2 << dec << endl;
return 0;
}
-----------------------
$ gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu/bin/i686-unknown-linux-gnu-g++
-O0 -W -Wall -o foo foo.cpp
$ ./foo
data = 0123456789, datalen = 10
data = 23456789, datalen = 8
peek = 23456789, tmp = 8
peek = 456789, tmp = 6
peek = 6789, tmp = 4
peek = 89, tmp = 2
x = 23456789
len = 8
fld1 = 3031
fld2 = 3637
$ gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu/bin/i686-unknown-linux-gnu-g++
-O2 -W -Wall -o foo foo.cpp
$ ./foo
data = 0123456789, datalen = 10
data = 23456789, datalen = 8
peek = 23456789, tmp = 8
peek = 23456789, tmp = 6
peek = 23456789, tmp = 4
peek = 23456789, tmp = 2
x = 23456789
len = 8
fld1 = 3031
fld2 = 3233
