`error: unrecognized instruction` when compiling target `hexagon-unknown-linux-musl`

[Wyvern]

rustc 1.99.0-nightly (d453bdd8f 2026-08-14)
target: hexagon-unknown-linux-musl
build with -Zbuild-std

error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:279:1
    │
279 │ FUNCTION_BEGIN __save_r24_through_r27
    ╰╴━

error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:281:1
    │
281 │ FALLTHROUGH_TAIL_CALL __save_r24_through_r27 __save_r24_through_r25
    ╰╴━

error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:286:1
    │
286 │ FUNCTION_END __save_r24_through_r25
    ╰╴━

error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:289:1
error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:857:1
    │
857 │ FUNCTION_BEGIN __hexagon_modsi3
    ╰╴━

error: unrecognized instruction
    ╰╴
note: instantiated into assembly here
    ╭▸ <inline asm>:895:1
    │
895 │ FUNCTION_END __hexagon_modsi3
    ╰╴━

error: unrecognized instruction
     ╰╴
note: instantiated into assembly here
     ╭▸ <inline asm>:2662:1
     │
2662 │ FUNCTION_BEGIN __hexagon_divsi3
     ╰╴━

error: unrecognized instruction
     ╰╴
note: instantiated into assembly here
     ╭▸ <inline asm>:2710:1
     │
2710 │ FUNCTION_END __hexagon_divsi3
     ╰╴━

error: could not compile `compiler_builtins` (lib) due to 40 previous errors

it's different compared to #1240 , I'm not sure whether it's the same problem, but looks like LLVM mismatch.

Why previous 1.99 nightly such as 2026-08-13 and before can build successfully after #1241 fix landing until 2026-08-14, 1.99 has migrated to llvm23 quite some time.

Anyway, just report it for in-depth investigating.

[tgross35]

Could you print the rustc -vV of the known good and bad nightlies so we can get a list of commits in that range?

Also, cargo-bisect-rustc is pretty powerful and will bisect to a merge within a nightly, if you can run that and post the output it might be helpful.

Cc again target maintainers @androm3da @quic-mliebel

[tgross35]

@Wyvern mind retrying with the latest nightly? The fix for that other issue synced back.

[Wyvern]

@tgross35 Ok, tried rustc 1.100.0-nightly (f7d782a3b 2026-08-19), problem disappeared, thanks for quick fix!

[tgross35]

No clue what fixed it but I don't think it was me, glad it's resolved anyway :)