From: "John (Eljay) Love-Jensen" <eljay@adobe.com>
To: "NightStrike" <nightstrike@gmail.com>,
"Tom St Denis" <tstdenis@ellipticsemi.com>
Cc: "J.C. Pizarro" <jcpiza@gmail.com>,
"Galloth" <lordgalloth@gmail.com>, <gcc-help@gcc.gnu.org>
Subject: RE: reduce compilation times?
Date: Tue, 27 Nov 2007 19:41:00 -0000 [thread overview]
Message-ID: <EDC8DDD212FEB34C884CBB0EE8EC2D9103B25E0A@namailgen.corp.adobe.com> (raw)
In-Reply-To: <b609cb3b0711271121p57206b2br87c6a6c99309255d@mail.gmail.com>
Hi NightStrike,
> Is there a difference in the speed of the resulting program when everything is split into many object files instead of being combined into a single main.c ...?
There may be a negative small performance impact in a resulting program that is split into many object files instead of being combined into a single main.c. (My expectation is that, overall, the performance impact will be negligible if it is even measurable.)
There may be a few interoperating routines that are strongly negatively impacted by being split into many object files instead of being combined into a single object file. (My expectation for these particular routines is that they should be heavily optimized, perhaps even being rewritten in lovingly handcrafted assembly -- assuming assembly chops are superior to the optimizing compiler's amazing optimizations.) If not re-written in hand coded assembly, at least having performance critical routines' code hand-tweaked to allow the GCC optimizer to do it's best to optimize it would be prudent (including using inline functions, and avoiding the anti-patterns that cripple optimization).
The way to assess those routines is through profiling.
GCC does not do "holistic" optimizations (yet). In contrast, LLVM does "holistic" optimizations.
>... or is the resulting binary identical bit for bit?
No, the resulting binary is not identical bit-for-bit.
It should be identical output for identical input. (Barring non-compliant or undefined behavior code, of course.)
HTH,
--Eljay
next prev parent reply other threads:[~2007-11-27 19:35 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-27 16:07 J.C. Pizarro
2007-11-27 16:19 ` Brian Dessent
2007-11-27 16:26 ` J.C. Pizarro
[not found] ` <5abcb5650711270804o171e1facr565beec70314af75@mail.gmail.com>
2007-11-27 16:41 ` J.C. Pizarro
2007-11-27 16:46 ` Tom St Denis
2007-11-27 17:16 ` J.C. Pizarro
2007-11-27 17:46 ` Tom St Denis
2007-11-27 18:26 ` Wesley Smith
2007-11-27 19:35 ` NightStrike
2007-11-27 19:41 ` John (Eljay) Love-Jensen [this message]
2007-11-27 19:49 ` Tom St Denis
2007-11-28 9:19 ` Brian Dessent
2007-11-28 12:07 ` Tom St Denis
2007-11-28 12:35 ` Brian Dessent
2007-11-27 17:44 ` Vladimir Vassilev
[not found] ` <998d0e4a0711271310k657b791cy6ad5cc5721105f4c@mail.gmail.com>
2007-11-27 22:30 ` J.C. Pizarro
-- strict thread matches above, loose matches on Subject: below --
2007-11-28 16:06 J.C. Pizarro
2007-11-28 16:16 ` Tom St Denis
2007-11-28 16:34 ` J.C. Pizarro
2007-11-28 18:18 ` Tom St Denis
2007-11-28 13:56 Duft Markus
2007-11-28 14:35 ` Tom St Denis
2007-11-29 0:23 ` Tim Prince
2007-11-28 13:25 Duft Markus
2007-11-28 13:26 ` Tom St Denis
2007-11-28 12:36 Duft Markus
2007-11-28 7:57 Duft Markus
2007-11-28 12:01 ` J.C. Pizarro
2007-11-28 12:28 ` Tom St Denis
2007-11-28 12:49 ` Fabian Cenedese
2007-11-28 13:03 ` Tom St Denis
2007-11-28 12:52 ` J.C. Pizarro
2007-11-28 13:17 ` Tom St Denis
2007-11-28 13:40 ` J.C. Pizarro
2007-11-28 13:51 ` Tom St Denis
2007-11-28 13:59 ` Tom St Denis
2007-11-28 15:51 ` John (Eljay) Love-Jensen
2007-11-28 13:30 ` Ted Byers
2007-11-28 12:12 ` John (Eljay) Love-Jensen
2007-11-28 12:31 ` J.C. Pizarro
2007-11-28 12:39 ` Tom St Denis
2007-11-28 12:54 ` John (Eljay) Love-Jensen
2007-11-28 12:18 ` Tom St Denis
2007-11-28 13:09 ` Ted Byers
2007-11-27 10:04 mahmoodn
2007-11-27 11:11 ` Andrew Haley
2007-11-27 11:15 ` mahmoodn
2007-11-27 11:30 ` Andrew Haley
2007-11-27 12:20 ` mahmoodn
2007-11-27 12:25 ` John Love-Jensen
2007-11-27 15:27 ` Tim Prince
2007-11-27 14:07 ` Andrew Haley
2007-11-28 9:01 ` mahmoodn
2007-11-28 12:11 ` John (Eljay) Love-Jensen
2007-11-30 9:15 ` mahmoodn
2007-11-30 13:33 ` mahmoodn
2007-11-27 15:48 ` Sven Eschenberg
2007-11-27 16:27 ` Andrew Haley
2007-11-27 18:51 ` Sven Eschenberg
2007-11-27 19:21 ` Andrew Haley
2007-11-27 20:43 ` Sven Eschenberg
2007-12-01 12:20 ` mahmoodn
2007-12-03 16:14 ` Andrew Haley
2007-12-04 11:23 ` mahmoodn
2007-12-04 12:19 ` Tom Browder
2007-12-05 7:44 ` mahmoodn
2007-12-05 10:24 ` Tom Browder
2007-12-05 10:29 ` mahmoodn
2007-11-27 13:48 ` John Love-Jensen
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