[cfe-dev] clang and Crypto++

[Marshall Clow]

On Jan 5, 2011, at 9:53 AM, Eric Christopher wrote:

> 
> 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 :)

Done.
	<http://llvm.org/bugs/show_bug.cgi?id=8916> for the optimizer
	<http://llvm.org/bugs/show_bug.cgi?id=8917> for the front end.

-- Marshall