clang++ 3.3 issue (excessively slow compile vs. gcc 4.6 in just one file of a port)

[Matthias Andree]

Am 19.11.2013 08:49, schrieb Dimitry Andric:
> On 18 Nov 2013, at 23:54, Matthias Andree <mandree at FreeBSD.org> wrote:
> ...
>> Uploaded. http://people.freebsd.org/~mandree/ has:
>>
>> <http://people.freebsd.org/~mandree/ipsharpen.ii.xz>: the xzipped .ii
>> file (unpacked: 6.5 MB)
>>
>> <http://people.freebsd.org/~mandree/ipsharpen-compile%2bwarnings.txt>:
>> compiler command line (make VERBOSE=1 MAKE_JOBS_UNSAFE=yes)
>> and early warnings.
> 
> Ok, this looks like http://llvm.org/PR16474 , which has a relatively
> simple fix.  I have attached it, can you please try it out?  You can
> just apply the patch to /usr/src and do:
> 
> make -C /usr/src/lib/clang
> make -C /usr/src/usr.bin/clang/clang
> sudo make -C /usr/src/usr.bin/clang/clang install
> 
> It should basically recompile just one file, and re-link the clang
> executable.  I tried building ipsharpen.ii at -O3, and it uses about
> 20 seconds now (on my relatively slow VM).

Dimitry,

thanks.

The patch speeds up the compile by one and a half orders of magnitude,
and we're down to 30 s for my VM and compiling the .ii file.

The .cc now compiles in 22 s, rather than 500 s.

Excellent, problem solved!

Can we commit this (what the LLVM PR calls "regression") fix so it
becomes part of 10.0-RELEASE?

Best regards
Matthias


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