[Bug middle-end/33638] New: optimization bug: wrong code with -fforce-addr

["manfred99 at gmx dot ch" <gcc-bugzilla at gcc dot gnu dot org>]

I have a rather nasty optimization issue with gfortran (as of yesterday). 
As I think it could be an optimization issue and not an gfortran frontend
issue, so I assigned it to the middle-end.

I narrowed my problem to one single fortran function. If I compile this
function with
"gfortran -O2 -march=pentium4" the output is OK, using
"gfortran -O2 -march=pentium4 -fforce-addr" produces wrong output.

When reducing optimization level to "-O1", the issue vanishes for all tried
flag combinations.
If I comment out a particular non-functional line in this code, the issue goes
away:

if (always_true) then
  ....
else
   this_line_commented_out_makes_it_working_again
   ....
endif

I will add assembler output of original, non-working code as well as
of working code when commenting the non-functional line, both compiled with
"gfortran -O2 -march=pentium4 -fforce-addr -S comunpack.f"
Function code is added as well.


Further data points:
- output of -fdump-tree-optimized is the same for both the working and the 
    broken case (of the original function, not the line commenting test).
- there are differences in assembler output though.
- the code calls C functions.
- I could reproduce this issue on an different, non-pentium4 machine 
    using the same flags.
- the flag -march=pentium4 is necessary to trigger the issue.


-- 
           Summary: optimization bug: wrong code with -fforce-addr
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: manfred99 at gmx dot ch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33638