Enable split_debuginfo=packed/unpacked for RISC-V

[kxxt]

The packed/unpacked options are disabled for this target in #120518.
Now they are implemented in LLVM 22.1: llvm/llvm-project#56642 (comment).

Note that I am not sure about the minimum supported LLVM version for rustc.
This PR could wait for some time if the minimum supported LLVM version is below 22.1 on nightly/1.96.0.

Tests done

• build/host/stage1/bin/rustc --edition=2024 src/main.rs --crate-type bin -C debuginfo=2 -C split-debuginfo=packed --target riscv64gc-unknown-linux-gnu -C linker=riscv64-linux-gnu-gcc
• build/host/stage1/bin/rustc --edition=2024 src/main.rs --crate-type bin -C debuginfo=2 -C split-debuginfo=unpacked --target riscv64gc-unknown-linux-gnu -C linker=riscv64-linux-gnu-gcc

run `./x test` on riscv64 linux to confirm the re-enabled tests pass. The only failure is #148748

failures:

---- [ui] tests/ui/explicit-tail-calls/become-indirect-return.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/home/kxxt/rust/build/riscv64gc-unknown-linux-gnu/stage1/bin/rustc" "/home/kxxt/rust/tests/ui/explicit-tail-calls/become-indirect-return.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/home/kxxt/.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/home/kxxt/rust/vendor" "--sysroot" "/home/kxxt/rust/build/riscv64gc-unknown-linux-gnu/stage1" "--target=riscv64gc-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/home/kxxt/rust/build/riscv64gc-unknown-linux-gnu/test/ui/explicit-tail-calls/become-indirect-return/a" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/home/kxxt/rust/build/riscv64gc-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
rustc-LLVM ERROR: failed to perform tail call elimination on a call site marked musttail
------------------------------------------

---- [ui] tests/ui/explicit-tail-calls/become-indirect-return.rs stdout end ----

failures:
    [ui] tests/ui/explicit-tail-calls/become-indirect-return.rs

test result: FAILED. 19741 passed; 1 failed; 404 ignored; 0 measured; 0 filtered out; finished in 541.49s

Some tests failed in compiletest suite=ui mode=ui host=riscv64gc-unknown-linux-gnu target=riscv64gc-unknown-linux-gnu
Build completed unsuccessfully in 0:11:53

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(See the Target Tier Policy.)

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[kxxt]

This PR could wait for some time if the minimum supported LLVM version is below 22.1 on nightly/1.96.0.

Or is there any internal conditional compilation mechanism that I could use to disable packed/unpacked if the LLVM version is less than 22.1?

[TaKO8Ki]

It seems that the minimum supported LLVM version is 21.x. #153684

rust/src/bootstrap/src/core/build_steps/llvm.rs

Lines 633 to 637 in d1d3ef4

	if let (Some(major), Some(_minor)) = (parts.next(), parts.next())
	&& major >= 21
	{
	return;
	}

Or is there any internal conditional compilation mechanism that I could use to disable packed/unpacked if the LLVM version is less than 22.1?

I don’t think there’s an existing generic mechanism for this.

[kxxt]

Or is there any internal conditional compilation mechanism that I could use to disable packed/unpacked if the LLVM version is less than 22.1?

I don’t think there’s an existing generic mechanism for this.

Thanks! Then it's better waiting for the bump of minimum LLVM version to 22.1.

[kxxt]

@rustbot label A-LLVM O-riscv