[cfe-dev] clang and Crypto++

[Eric Christopher]

On Jan 5, 2011, at 9:51 AM, Marshall Clow wrote:

> 
> 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?
> 
> FWIW, it's not all about the optimizer:
> $ time g++ -DNDEBUG -g -O2 -arch x86_64 -arch i386 -DCRYPTOPP_DISABLE_ASM -pipe -c sha.cpp 
> real 1.662s

Probably 2 bugs then :)

-eric