On 1/4/21 11:28 AM, Jeff Law wrote:
On 1/4/21 12:22 PM, Tom Stellard wrote:
On 12/30/20 11:52 AM, Ben Cotton wrote:
https://fedoraproject.org/wiki/Changes/LTOBuildImprovements
== Summary ==
Currently all packages that are not opted out of LTO include
-ffat-lto-objects in their build flags. This proposal would remove
-ffat-lto-objects from the default LTO flags and only use it for
packages that actually need it.
== Owner ==
* Name: [[User:law | Jeff Law]]
* Email: law@xxxxxxxxxx
== Detailed Description ==
-ffat-lto-objects was added to the default LTO flags to ensure that
any installed .o/.a files included actual compiled code rather than
just LTO bytecodes (which are stripped after the install phase).
However, that is wasteful from a compile-time standpoint as few
packages actually install any .o/.a files.
This proposal would remove -ffat-lto-objects from the default LTO
flags and packages that actually need the option would have to opt-in
via an RPM macro in their .spec file. This should significantly
improve build times for most packages in Fedora.
What is this macro going to be called? I would like to get an early
start on updating my packages.
No idea. I'm open to suggestions.
IIRC we had kicked around the idea of having the clang/llvm path
instantiate the LTO bytecodes in .o/.a files, which would avoid these
issues for packages using clang/llvm. Is that something we still want
to pursue? I vaguely recall discussing this with David B. and he came
up with a reason why that needed to happen before brp-strip-lto, but I
can't remember any of the details at this point.
Yes, David is still working on a solution for clang/llvm. I'm not sure,
though, at what point in the RPM build process the LTO bytecode will get
codegen'd.
-Tom
Jeff
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