Re: GNAT and register allocation

[Stephen Leake <stephen_leake@stephe-leake.org>]

Georg Bauhaus <rm.dash-bauhaus@futureapps.de> writes:

> On 21.04.12 14:10, Stephen Leake wrote:
>
>>> I must use one set of options for an entire program in this case.
>>
>> Why?
>
> This requirement is likely a fact (external) that we can't change.
> We may try one day.

Sounds like a bad rule; do they tell you to use C? or to use -O3 instead
of -O2? This is a decision that should be left to the people running the
Makefiles!

>> gpr files give you a way to apply different compilation options to
>> different files. There are _lots_ of low-level gcc options controlling
>> inline and other optimizations; see gnat user guide, section 3.10.
>
> Controlling inline expansion with GCC's -f[no]-inline[-*] can
> require that the entire program be reorganized. Consider a call chain:
>
> A
> -> B
> --> C
> ---> D
>
> I want to specify that D be expanded inline into C,
> but also want to prevent C from being expanded into B.
> That is, B should actually call C. Right now, the bodies
> of B, C, and D are neighbors in the same scope.
>
> In this case, a possible solution seems to be to arrange
> for separate compilation units. 

Yes.

> Specify -fno-inline-functions for the translation of B, and enable
> inline expansion for C and D. Is this correct? OR will the "outer"
> inline prevention override the "inner"?

I don't know; the manual isn't very clear. A little experimentation
would tell.

> I'm also no sure yet whether or not this arrangement will be possible
> using Ada's feature for separate compilation ("separate" keyword),
> or whether I would have to make a child package containing C and D.
> (IIRC, GNAT uses slightly different rules for subprograms declared
> separate in other subprograms than for subprograms declared separate
> in (non-generic?) packages.)

Right.

> If this procedure adequately describes how to achieve inline control,
> then I will find a compiler pragma a little easier.

I guess you mean 'a pragma I can include in the current source files,
that applies to specific subprograms'.

Yes, that would be simpler. The command line options have the advantage
of being available now :).

-- 
-- Stephe