We can use the same logic to avoid rebuilding LLD if the host version is the same as the in-tree version. Because LLD requires LLVM libraries I think we should just roll the eventual LLD version check into the existing MK_SYSTEM_COMPILER test in Makefile.inc1.

I'll test this patch sometime within the next 24-72 hours. As it stands, the logic looks completely fine to me. Thanks for working on this!

Patch tested successfully. Other than the typo @lifanov noted, the patch looks good to me.

I'm not sure of the minimal set of objects needed to build LLD but it's some subset of the combination of ${SRCS_MIN}, ${SRCS_MIW}, and ${SRCS_XDL} in lib/clang/libllvm. Perhaps later we can extend libllvmminimal to optionally include LLD's requirements.

In D9487#196457, @emaste wrote:

I'm not sure of the minimal set of objects needed to build LLD but it's some subset of the combination of ${SRCS_MIN}, ${SRCS_MIW}, and ${SRCS_XDL} in lib/clang/libllvm. Perhaps later we can extend libllvmminimal to optionally include LLD's requirements.

I'd like to revert the MK_SYSTEM_COMPILER piece. It's unfortunate that it basically forces SYSTEM_COMPILER off for several architectures.

I tested reverting this and building arm64.aarch64 with SYSTEM_COMPILER triggered and everything built fine.

~/git/freebsd # /usr/obj/arm64.aarch64/root/git/freebsd/tmp/usr/bin/ld -V
LLD 4.0.0 (FreeBSD 297347) (compatible with GNU linkers)
~/git/freebsd # ls -al /usr/obj/arm64.aarch64/root/git/freebsd/tmp/usr/bin
total 23926
drwxr-xr-x   2 root  wheel        13 Apr 28 12:59 ./
drwxr-xr-x  13 root  wheel        13 Apr 28 12:36 ../
-rwxr-xr-x   1 root  wheel    822320 Apr 28 12:59 addr2line*
-rwxr-xr-x   1 root  wheel   1015352 Apr 28 12:59 ctfconvert*
-rwxr-xr-x   1 root  wheel    875240 Apr 28 12:59 ctfmerge*
lrwxr-xr-x   1 root  wheel         6 Apr 28 12:58 ld@ -> ld.lld
-rwxr-xr-x   1 root  wheel  38882448 Apr 28 12:58 ld.lld*
-rwxr-xr-x   1 root  wheel    847680 Apr 28 12:59 nm*
-rwxr-xr-x   2 root  wheel   1034184 Apr 28 12:59 objcopy*
-rwxr-xr-x   1 root  wheel    641328 Apr 28 12:59 size*
-rwxr-xr-x   1 root  wheel    635568 Apr 28 12:59 strings*
-rwxr-xr-x   2 root  wheel   1034184 Apr 28 12:59 strip*
-rwxr-xr-x   1 root  wheel    568552 Apr 28 12:59 sysinit*

libllvmminimal and libllvm were still built and lld was able to link and execute.

What problem was this trying to avoid?

Reverted in rS317608. This was a temporary measure to fix build breakage before rS316647 (LLD_BOOTSTRAP) went in.

It's unfortunate that it basically forces SYSTEM_COMPILER off for several architectures.

It should have affected only arm64.aarch64, no?