[Bug target/39386] New: different computation results for O1 and O0 executables

[jxyang at cs dot utah dot edu]

This is seen on the version of avr-gcc 4.3.3 that gets built by the script that
comes with FemtoOS 0.88.

The program performs simple arithmatic and logical operations on a global
variable, and store the result in register R30:R31.

If the program is compiled with "avr-gcc -mmcu=atmega128 -O0", the final result
is 00. On the other hand, if the program is compiled with "avr-gcc
-mmcu=atmega128 -O1", the final result is 0xFF. Compiling at O2 gives me 0xFF
too.

Obviously, avr-gcc compiled the program wrong at one of the these optimization
levels.

This bug is observed in avr studio 4.15.


-- 
           Summary: different computation results for O1 and O0 executables
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jxyang at cs dot utah dot edu
 GCC build triplet: --target=avr --with-gnu-ld --with-gnu-as --enable-
                    languages=c,c+
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39386