[m-dev.] gcc abort on runtime/mercury_atomic_ops.c

[Julien Fischer]

On Mon, 22 Oct 2007, Zoltan Somogyi wrote:

> On my laptop (alys, a Dell Inspiron 9400 with an Intel T2500 CPU), I get
> the following error from gcc:
>
> ../scripts/mgnuc --grade asm_fast.gc      --c-debug --no-ansi   --   -O0 -g    -c mercury_atomic_ops.c -o mercury_atomic_ops.o
> mercury_atomic_ops.c: In function `MR_compare_and_swap_word':
> mercury_atomic_ops.c:22: error: can't find a register in class `GENERAL_REGS' while reloading `asm'
>
> The output of gcc -v is:
>
> Reading specs from /usr/lib/gcc/i486-linux-gnu/3.4.6/specs
> Configured with: ../src/configure -v --enable-languages=c,c++,f77,pascal --prefix=/usr --libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --program-suffix=-3.4 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --with-tune=pentium4 i486-linux-gnu
> Thread model: posix
> gcc version 3.4.6 (Ubuntu 3.4.6-1ubuntu2)
>
> The error goes away if I delete the -O0 from the list of command line
> arguments. (I originally added it via Mmake.runtime.params, since I was
> trying to debug something in the runtime.)
>
> Does anyone know what specifically causes the incompatibility of -O0
> with this inline asm code? (I mean beside the x86's lack of registers,
> especially after we reserve some.)

I think we should make the code runtime/mercury_atomic_ops.[ch] 
conditional on MR_LL_PARALLEL_CONJ being defined (at least for the time
being.)  Any code that uses the functions in mercury_atomic_ops is
already condtional on that macro anyway.

Julien.
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