Hi,
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, I post it here,
the fortran list was not able to help so far.
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
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.
I'm in a loss where to search for the real cause. Has anybody a hint how to
proceed further?
Should I post the code of this function here on the list (~300 LOC)?
Thanks,
Manfred
