[cfe-users] Improve compile performance when using Clang 3.6

Alexey Samsonov vonosmas at gmail.com
Wed Apr 1 18:13:11 PDT 2015

On Wed, Apr 1, 2015 at 5:18 PM, Jeffrey Walton <noloader at gmail.com> wrote:

> Hi Everyone,
> I just downloaded and built Clang 3.6. It appears performance has
> dropped considerably from Clang 3.2 through 3.5 (I've been
> building/using it for that long).
> Is there anything obvious I am missing that might affect the
> performance between 3.5 and 3.6? Like is something enabled that used
> to be disabled or missing?
> Otherwise, below is what a typical compiler invocation looks like. In
> the past, it performed fine. Does it set off any red flags for anyone?
> For completeness, I'm trying to run self tests under the sanitizers.
> I'm interested in the dynamic analysis at this point, and not static
> analysis provided by ccc-analyze and friends.

Interesting. Could you share the performance numbers, and try to figure out
which specific sanitizer
is causing a problem (i.e. try to compare just -fsanitize=address, and then
various flavors of -fsanitize=undefined
one by one: -fsanitize=shift, -fsanitize=null etc.). We are not aware of
known performance degradation under
sanitizers in 3.6 release.

> Thanks in advance.
> ====================
> $ make static
> /usr/local/bin/clang++ -DNDEBUG -g3 -Os -fPIC -fsanitize=address
> -fsanitize=undefined -Wall -Wno-tautological-compare -Wno-unused-value
> -Wno-unused-variable -Wno-unused-parameter -Wno-unused-function
> -DCRYPTOPP_DISABLE_ASM -pipe -c 3way.cpp
> /usr/local/bin/clang++ -DNDEBUG -g3 -Os -fPIC -fsanitize=address
> -fsanitize=undefined -Wall -Wno-tautological-compare -Wno-unused-value
> -Wno-unused-variable -Wno-unused-parameter -Wno-unused-function
> -DCRYPTOPP_DISABLE_ASM -pipe -c adler32.cpp
> ...
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> cfe-users at cs.uiuc.edu
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Alexey Samsonov
vonosmas at gmail.com
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