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Re: GCC-4.5.0 comparison with previous releases and LLVM-2.7 on SPEC2000 for x86/x86_64
2010/11/16 Jan Hubicka <hubicka@ucw.cz>:
>> On Mon, Nov 15, 2010 at 5:39 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> >> > Fortunately linker plugin solves the problem here and this is why I want to
>> >> > have it by default. ?GCC then can do effectively -fwhole-program for binaries
>> >> > (since linker knows what will be bound elsewhere) and take advantage of
>> >> > visibility((hidden)) hints for shared libraries same way. ?Most of important
>> >> > shared libraries gets visibility ((hidden)) right.
>> >> >
>> >> > It is sad that LTO w/o linker plugin doesn't give that much benefits.
>> >> > Ideas are welcome here.
>> >>
>> >> Linker feedback will be limited here -- mostly global variable
>> >> aliasing (as I remember only 2/3 spec programs benefit from it), it
>> >> helps ?You don't get whole program points-to, whole program mod-ref
>> >> (with context sensitivity), whole program structure layout. The latter
>> >> are the real kickers (in terms of SPEC performance), but promoting LTO
>> >> with those numbers can be misleading as many programs won't get it.
>> >
>> > Well, I am speaking of our linker plugin here. ?What it does is to pass GCC
>> > resolution information so it knows what symbols are bound externally. Since
>> > typically you link LTO alone or with small non-LTO part, most of symbols are
>> > not bound and thus effecitvely you get -fwhole-program (-fwhole-program just
>> > declare everything static except for main ())
>> >
>> > We don't really do whole program points-to or structure layout.
>>
>> gcc will eventually, right?
>
> Sure hope so ;)
> We really need to solve scalability with our IPA points-to and make it
> compatible with WHOPR.
>>
>> > Mod-ref is just
>> > simple ipa-reference code. How you get context sensitivity on mod/ref?
>>
>> mod-ref relies on points-to. With context sensitive points-to, you can
>> also get CS mod-ref -- basically mod-ref info per callsite.
>
> Ah sure, I was too focused on our current "mod/ref" :)
Btw, IPA-PTA also performs mod/ref analysis (but of course it is
context insensitive).
Richard.
> Honza
>