Support s390x z13 vector ABI

[taiki-e]

cc #130869

This resolves the following fixmes:

• rust/compiler/rustc_target/src/abi/call/s390x.rs

  Lines 1 to 2 in 58420a0

  	// FIXME: The assumes we're using the non-vector ABI, i.e., compiling
  	// for a pre-z13 machine or using -mno-vx.

• rust/compiler/rustc_target/src/spec/targets/s390x_unknown_linux_gnu.rs

  Lines 9 to 11 in 58420a0

  	// FIXME: The ABI implementation in abi/call/s390x.rs is for now hard-coded to assume the no-vector
  	// ABI. Pass the -vector feature string to LLVM to respect this assumption.
  	base.features = "-vector".into();

Refs: Section 1.2.3 "Parameter Passing" and section 1.2.5 "Return Values" in ELF Application Binary Interface s390x Supplement, Version 1.6.1 (lzsabi_s390x.pdf in https://github.com/IBM/s390x-abi/releases/tag/v1.6.1)

Depends on #127731. (The first commit is from it and the second commit is fix errors happened after rebased it.)

This PR extends #127731 's ABI check for that PR to reject cases where vector target feature is disabled.
If we do not do ABI check, we run into the ABI problems as described in #116558 and #130869 (comment), and the problem of the compiler generating strange code (#131586 (comment)).

cc @uweigand

@rustbot label +O-SystemZ +A-ABI

[rustbot]

r? @jieyouxu

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[jieyouxu]

r? compiler

[taiki-e]

Fixed #[repr(C)] wrapper test and added #[repr(transparent)] wrapper test.

[taiki-e]

For now, this is planned not to be completed until #127731 is merged.

@rustbot label -S-waiting-on-review, +S-blocked

[uweigand]

In addition to the problem mentioned inline, we should also verify that building with soft-float works as expected. This option implicitly disables any use of floating-point or vector registers, and therefore also disables use of the vector facility. I believe the LLVM back-end should handle that logic correctly, but it would be good to have the test check.

[uweigand]

It's also incorrect. Without the vector feature, vector types of any length are supposed to be passed via implicit reference, which in the case means a pointer in %r2. The body of the function should simply be:

lg %r2, 0(%r2)

Not sure what exactly the compiler is doing here, but it appears to have scalarized the input and pass it as 8 distinct one-byte arguments ...

[taiki-e]

This case and soft-float case should eventually result in a compilation error once the ABI check is implemented, and I will add UI tests for these cases once the ABI check is implemented.

[uweigand]

Fair enough. I just wanted to point out the incorrect code, in case we do end up going back to supporting the no-vector case.

[bors]

☔ The latest upstream changes (presumably #131747) made this pull request unmergeable. Please resolve the merge conflicts.