optimization/6330: tiny C++ prog broken under -O1

[David Hanney]

Many thanks for your prompt response!

I assumed (wrongly, I know) that because "the cast-output is the same four 
bytes
as the cast-input" that it would be at the same address (union-style). My bad.

But, given this behavior-set ..

    gcc with plain     C++ works.            (no compiler warning)
    gcc with optimized C++ doesn't work.     (no compiler warning)
    gcc with           C   doesn't compile.
   (under gcc 2.95.4 and gcc 3)

.. would a compiler warning be useful here?

Especially as the pointer may be formed implicitly via a reference
(as shown in the code quoted below)

cheers,

DH

-------------------------------------------
#!/bin/sh

# what compiler/OS version is it?
gcc-3.0 -v
uname -a

# create a program
echo '#include <stdio.h>' > x.cpp
echo '#include <stdlib.h>' >> x.cpp
echo 'typedef unsigned char byte;' >> x.cpp;
echo 'typedef byte *pbyte;' >> x.cpp;
echo 'void change(pbyte &z) { z = (pbyte)"correct"; }' >> x.cpp
echo 'int main() {' >> x.cpp
echo '    char *s = "incorrect";' >> x.cpp
echo '    change((byte*)s);' >> x.cpp
echo '    printf("%s\n", s);' >> x.cpp
echo '    exit(0);' >> x.cpp
echo '}' >> x.cpp

# compile and run it
gcc-3.0 x.cpp
./a.out

# compile and run The Same Program optimized
gcc-3.0 -O1 x.cpp
./a.out
-------------------------------------------





At 00:41 18/04/02 +0000, rth@gcc.gnu.org wrote:
>Synopsis: tiny C++ prog broken under -O1
>
>State-Changed-From-To: open->closed
>State-Changed-By: rth
>State-Changed-When: Wed Apr 17 17:41:35 2002
>State-Changed-Why:
>     Not a bug.  You have taken the address of a temporary.
>     You wanted "change((byte**)&s)".
>
>http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6330 
>