wrong code with -fforce-addr

[Manfred Schwarb]

Hi,

I have a rather nasty wrong code issue with recent gfortran (of yesterday) at higher optimisation levels.
It's in a large program with a lot of legacy things in it, mixed c and fortran (66-95).

I could track down the error to one subroutine with 300 LOC of fortran95 (well, fortran66 with
some few fortran95 statements).

With "-O2 -fforce-addr", the program produces the correct output,
with "-O2 -march=pentium4 -fforce-addr" the output is wrong.
If I omit "-fforce-addr", the output is always correct.
At optimisation level "-O1", i.e. "-O1 -march=pentium4 -fforce-addr", the output is OK.

The output of -fdump-tree-optimized is the same for the working and non-working case.
As expected, there are differences in the assembler output, however, I do
not speak assembler.

As this program has a lot of iterations and a lot of data IO, it seems rather unrealistic
to poke with a debugger or putting in print statements.

Has anybody an idea how to narrow things?
What would be the appropriate debug output to see what is going wrong?

Thanks,
Manfred