[Bug target/52474] Regression: AVR-GCC: arithmetics produce completely wrong result

["gjl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52474

--- Comment #4 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2012-03-14 11:11:47 UTC ---
Created attachment 26889
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26889
main.s: FSF Assembler output

Here is the assembler output of the main mudule generated with

$ avr-gcc -mmcu=atmega168 -S main.c -O2 -dp

If you see the same code your problem is somewhere else.

If you see different code for these options, the problem comes from non-FSF
changes. As indicated in comment #0 there is a call to __mulhisi3 which is not
present in the attached main.s and is not part of the FSF sources, see
http://gcc.gnu.org/viewcvs/branches/gcc-4_5-branch/gcc/config/avr/avr.md?content-type=text%2Fplain&view=co

__mulhisi3 is present in avr-gcc 4.7 but that implementation is from scratch
and does not use __mulhisi3 patches floating around.

(In reply to comment #3)
> OK, so talking to the debian maintainer, the GCC version I'm using is based
> upon patches available here: 
> 
> http://distribute.atmel.no/tools/opensource/avr-gcc/
> 
> Here is a test case. I'm unsure how to make a test case for code
> to be executed on a microcontroller because I need to make some
> assumptions about the board so that the result can be shown to
> the user somehow (flash a LED, whatever...)

Please, do not make assumptions on the hardware. The more assumptions you make
the more artificial barriert you build up. Just can use exit and abort from
stdlib.h to indicate the problem.

If you want to avoid that GCC uses knowledge on functions, you can

short __attribute__((noinline,noclone))
query (void)
{
  return 0;
}