[cfe-dev] clang and Crypto++
Eric Christopher
echristo at apple.com
Wed Jan 5 09:52:41 PST 2011
On Jan 5, 2011, at 9:45 AM, Marshall Clow wrote:
> On Jan 5, 2011, at 9:31 AM, Douglas Gregor wrote:
>> On Jan 5, 2011, at 9:06 AM, Marshall Clow wrote:
>>
>>> After Doug fixed bug #7851 yesterday (thanks, Doug!), I decided to see if crypto++ <http://www.cryptopp.com/> would build with clang TOT.
>>>
>>> Answer: No, it does not.
>>>
>>> There are three problems:
>
> [ #1 and #2 snipped out ]
>
>>
>>> 3) clang is much, much slower than gcc 4.2.1 when building crypto++.
>>> On my 2007 MacPro:
>>> gcc takes 8m40s to build.
>>> clang (TOT this morning) takes much longer; there is one file - sha.cpp which takes over 30 minutes, if it ever does finish, but all the other files combined take more than 45 minutes.
>>
>>
>> Naturally, we'd like to know where in clang this time is going. Is it the front end (-fsyntax-only)? The optimizer (> -O0), and if so, which one(s)?
>
> Looks like the optimizer.
>
> $ time clang++ -Wno-tautological-compare -DNDEBUG -g -arch x86_64 -arch i386 -DCRYPTOPP_DISABLE_ASM -pipe -fsyntax-only sha.cpp
> real 6.234s
> $ time clang++ -Wno-tautological-compare -DNDEBUG -g -arch x86_64 -arch i386 -DCRYPTOPP_DISABLE_ASM -pipe -c sha.cpp
> real 7.863s
> $ time clang++ -Wno-tautological-compare -DNDEBUG -g -O1 -arch x86_64 -arch i386 -DCRYPTOPP_DISABLE_ASM -pipe -c sha.cpp
> real 17.882s
> $ time clang++ -Wno-tautological-compare -DNDEBUG -g -O2 -arch x86_64 -arch i386 -DCRYPTOPP_DISABLE_ASM -pipe -c sha.cpp
> .... long, long time; I killed it after 30 minutes.
>
> How do I tell which one?
I'm guessing one of the loop ones, but if you file a bug with a preprocessed file we'll figure it out.
Thanks!
-eric
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