Re: IPA and LTO

[AJM-2 <mcpherson.aj@gmail.com>]

What you say is in line with my understanding, however when I instrument the
execute function of ipa-function-and-variable-visibility
(local_function_and_variable_visibility()) I note that:

gcc -flto a.c b.c
causes the pass to be called twice (presumably once per file).

If I split the compilation into two stages, then in the link stage
gcc -flto a.o b.o
the pass is never called.

Conversely, the gate of IPA-Points-to does seem to be called three times at
link time (presumably once for each file and then once for all together).  I
cannot discover the cause of the different behaviours here.


Diego Novillo-3 wrote:
> 
> On Wed, Jul 13, 2011 at 10:22, AJM-2 <mcpherson.aj@gmail.com> wrote:
> 
>> My question is whether LTO can be used in this way, to have a simple ipa
>> pass called once at link time with access to the function bodies, and if
>> so
>> how is this achieved?  cgraph_function_body_availability seems to only be
>> half the story.
> 
> Yes, it can.  You seem to be describing what GCC calls "simple IPA
> pass".  These are passes that cannot run in partitioned LTO mode, as
> they require the function bodies to operate.  Look for passes like
> pass_ipa_function_and_variable_visibility for an example of a simple
> IPA pass.
> 
> 
> Diego.
> 
> 

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