[m-rev.] for review: Document experience on AIX.

[Julien Fischer]

Hi Peter,

On Mon, 14 Jul 2014, Peter Wang wrote:

> On Fri, 11 Jul 2014 18:15:38 +1000, Julien Fischer <jfischer at opturion.com> wrote:
>>>
>>> You may need to use the IBM C compiler instead of gcc.  Pass
>>> "--with-cc=xlc"
>>> when configuring the Mercury installation, and use high-level C grades
>>> for better performance.
>>>
>>
>> One issue here is that the configure script, Mercury.options, mgnuc script,
>> compiler/compiile_target_code.m
>> and probably other places won't recognise xlc as a type of C compiler --
>> the type should default
>> to unknown, but may incorrectly default to GCC in spots.
>
> I found one instance with grep -i for "compiler[-_ ]type",
> in reserve_stack_size_flags.

I'm not sure what you grepped there.  I count at least six uses of
get_c_compiler_type in compiler/compile_target_code.m (admittedly, most
of them are workarounds for Visual C weirdness).

I suggest adding a cc_xlc alternative to the type
globals.c_compiler_type and also recognising the options variable
XLC_FLAGS (we already support GCC_FLAGS, CLANG_FLAGS etc).

> Here is an updated document for review.

That's fine although most of the various workarounds could (and should
IMO) be applied by automatically if we recognised xlc as a separate sort
of C compiler.  (Incidentally, I believe xlc has a GCC compatibility
wrapper.

For GCC 4.2 on AIX, I think you should make the configure script print
an error message saying that the version of GCC is too ancient and
broken and then abort.

Cheers,
Julien.