[PATCH v2] RISC-V: build: Allow LTO to be selected

[Nathan Chancellor]

On Tue, Oct 04, 2022 at 06:57:10PM -0700, Palmer Dabbelt wrote:
> > Allow LTO to be selected for RISC-V, only when LLD >= 14, since there is an
> > issue [1] in prior LLD versions that prevents LLD to generate proper
> > machine code for RISC-V when writing `nop`s.
> > 
> > I have tested enabling LTO for `defconfig`. The LLD took ~2m21s and ~3GiB
> > on our Intel Xeon Gold 6140 server and produced an 18MiB Image. The image
> > can boot to shell using an archriscv rootfs on QEMU.
> > 
> > I have also tested it for `allyesconfig` without COMPILE_TEST, FTRACE,
> > KASAN, and GCOV. The LLD took ~7h03m and ~335GiB on the server,
> > successfully producing a 1.7GiB Image. Unfortunately, we cannot boot this
> > image because the `create_kernel_page_table()` -> `alloc_pmd_early()` ->
> > `BUG_ON()` logic limits the image to be < 1GiB. Maybe we can fix it in a
> > separate patch further.
> > 
> > [1] https://github.com/llvm/llvm-project/issues/50505, resolved by LLVM
> >     commit e63455d5e0e5 ("[MC] Use local MCSubtargetInfo in writeNops")
> > 
> > Tested-by: Wende Tan <twd2.me at gmail.com>
> > Signed-off-by: Wende Tan <twd2.me at gmail.com>
> 
> Sorry for missing this, the v2 never made it to my inbox.  Not sure exactly
> what happened, but an off-list ping made it through.  I've put this on
> for-next, I don't have any way to test it because I don't have clang setup
> yet.
> 

Did this get dropped by accident? I do not see it in your tree.

Cheers,
Nathan