[llvm-dev] CMake option to disable LTO?

[Steve King via llvm-dev]

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
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[Mehdi Amini via llvm-dev]

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

[Steve King via llvm-dev]

On Wed, Jan 13, 2016 at 11:26 AM, Mehdi Amini <mehdi...@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.

[Duncan P. N. Exon Smith via llvm-dev]

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?

[Rafael Espíndola]

On 25 January 2016 at 09:19, Duncan P. N. Exon Smith via llvm-dev

<llvm...@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