llvm dev - Jan 2016 - CMake option to disable LTO?

Hello LLVM,
When building LLVM/Clang (debug build), linking takes too long.  I
notice that LTO is enabled now and guess that's to blame.  Is there a
CMAKE config option to disable LTO linking?  I can't seem to find
anything.

Thanks,
-steve

Hi,

There is no option (that I know of) to enable/disable LTO (it shouldn’t be
enabled) other than setting it explicitly in the CMAKE_C_FLAG/CMAKE_CXX_FLAG.

Are you sure LTO is enabled? What it the value of CMAKE_C_FLAG/CMAKE_CXX_FLAG in
your CMakeCache.txt?

— 
Mehdi

> On Jan 13, 2016, at 11:20 AM, Steve King via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello LLVM,
> When building LLVM/Clang (debug build), linking takes too long.  I
> notice that LTO is enabled now and guess that's to blame.  Is there a
> CMAKE config option to disable LTO linking?  I can't seem to find
> anything.
> 
> Thanks,
> -steve
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On Wed, Jan 13, 2016 at 11:26 AM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> Are you sure LTO is enabled? What it the value of
CMAKE_C_FLAG/CMAKE_CXX_FLAG in your CMakeCache.txt?
Thanks Mehdi, I think I'm mistaken about LTO.  During linking, my gcc
5.3 loads liblto_plugin.so and lto_wrapper and so on, but I don't see
the -flto option to actually enable it.  Must be something else
clogging my build.

I think it'd be a bug if you got LTO by default with a debug build.
What platform are you on?  What cmake command did you use when
configuring?
> On 2016-Jan-13, at 11:20, Steve King via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello LLVM,
> When building LLVM/Clang (debug build), linking takes too long.  I
> notice that LTO is enabled now and guess that's to blame.  Is there a
> CMAKE config option to disable LTO linking?  I can't seem to find
> anything.
> 
> Thanks,
> -steve
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On 25 January 2016 at 09:19, Duncan P. N. Exon Smith via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> I think it'd be a bug if you got LTO by default with a debug build.
> What platform are you on?  What cmake command did you use when
> configuring?
It is probably just an oddity of building with current gcc:


--------------------------------
gcc test.o -o test.so -shared -Wl,-debug
.....
usr/bin/ld -plugin
/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/liblto_plugin.so...
----------------------------

It always passes the plugin options to ld, even when not doing LTO.

Cheers,
Rafael