[Bug rtl-optimization/26663] New: Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[Bug rtl-optimization/26663] New: Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[steffen dot zimmermann at philips dot com]

The attached C++ code converts a floating point number from
our internal representation to IEEE format.

When run, the program should print a value of 144. This works
with gcc-3.3.6 at any optimization level (-O1 -- -O3). With
gcc-3.4.x and optimization level -O2 or -O3, it prints 42 instead.
I.e., it seems the "iFloat" variable in CMdilFloat::AsFloat() is
never modified.

Here's the output of the code with various vanilla gcc's, along
with their configuration:

$ uname -a
Linux xxx.xxx.com 2.6.9-22.0.2.ELsmp #1 SMP Thu Jan 5 17:13:01 EST 2006 i686
i686 i386 GNU/Linux

$ gcc-3.3.6/bin/g++ -v                            
Reading specs from
/home/steffenz/gcc/install/gcc-3.3.6/lib/gcc-lib/i686-pc-linux-gnu/3.3.6/specs
Configured with: ../gcc-3.3.6/configure
--prefix=/home/steffenz/gcc/install/gcc-3.3.6 --disable-nls
--enable-languages=c,c++
Thread model: posix
gcc version 3.3.6

$ gcc-3.3.6/bin/g++ -O1 -o test test.cpp && ./test
144

$ gcc-3.3.6/bin/g++ -O2 -o test test.cpp && ./test
144

$ gcc-3.3.6/bin/g++ -O3 -o test test.cpp && ./test
144

$ gcc-3.4.0/bin/g++ -v
Reading specs from
/home/steffenz/gcc/install/gcc-3.4.0/lib/gcc/i686-pc-linux-gnu/3.4.0/specs
Configured with: ../gcc-3.4.0/configure
--prefix=/home/steffenz/gcc/install/gcc-3.4.0 --disable-nls
--enable-languages=c,c++
Thread model: posix
gcc version 3.4.0

$ gcc-3.4.0/bin/g++ -O1 -o test test.cpp && ./test
144

$ gcc-3.4.0/bin/g++ -O2 -o test test.cpp && ./test
42

$ gcc-3.4.0/bin/g++ -O3 -o test test.cpp && ./test
42

$ gcc-3.4.6/bin/g++ -v
Reading specs from
/home/steffenz/gcc/install/gcc-3.4.6/lib/gcc/i686-pc-linux-gnu/3.4.6/specs
Configured with: ../gcc-3.4.6/configure
--prefix=/home/steffenz/gcc/install/gcc-3.4.6 --disable-nls
--enable-languages=c,c++
Thread model: posix
gcc version 3.4.6

$ gcc-3.4.6/bin/g++ -O1 -o test test.cpp && ./test
144

$ gcc-3.4.6/bin/g++ -O2 -o test test.cpp && ./test
42

$ gcc-3.4.6/bin/g++ -O3 -o test test.cpp && ./test
42


-- 
           Summary: Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or
                    gcc-3.3.6)
           Product: gcc
           Version: 3.4.6
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steffen dot zimmermann at philips dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26663

[Bug rtl-optimization/26663] Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[steffen dot zimmermann at philips dot com]

------- Comment #1 from steffen dot zimmermann at philips dot com  2006-03-13 13:12 -------
Created an attachment (id=11038)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11038&action=view)
C++ source code to reproduce the bug


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26663

[Bug rtl-optimization/26663] Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2006-03-13 13:37 -------
This is invalid as it violates C/C++ aliasing rules.

*** This bug has been marked as a duplicate of 21920 ***


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26663

[Bug rtl-optimization/26663] Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2006-03-13 14:15 -------
   * (u_32 *) pFloat = 0x7FFFFFFF; // NaN
That is violating C/C++ aliasing rules.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26663

[Bug rtl-optimization/26663] Wrong generated code with gcc-3.4.x -O2 (ok with -O1 or gcc-3.3.6)

[jbeitaharon at intrusic dot com]

------- Comment #4 from jbeitaharon at intrusic dot com  2006-03-13 14:40 -------
Subject: Re:  Wrong generated code with gcc-3.4.x
 -O2 (ok with -O1 or gcc-3.3.6)

Please take me off the CC list for this distribution.

I don't need the "encouragement" of knowing that many people experience 
similar frustrations with gcc's poor (or shall I say, uninformative) 
warning messages in the case of aliasing rule violations.

Thanks,
Jonathan

pinskia at gcc dot gnu dot org wrote:

>------- Comment #3 from pinskia at gcc dot gnu dot org  2006-03-13 14:15 -------
>   * (u_32 *) pFloat = 0x7FFFFFFF; // NaN
>That is violating C/C++ aliasing rules.
>
>
>  
>


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26663