add s390x z17 target features

[folkertdev]

tracking issue: #130869

earlier target features were added in #135630, and #135413 (comment) has some extra context on these new features.

r? @ghost
cc @uweigand

[folkertdev]

Based on that CI log, I believe what is happening is that rust still supportes LLVM 19 (because of linux distributions), and in that version these new target features are not yet present. So, we may need to wait until the lowest supported LLVM version also does support these target features.

[uweigand]

Hi @folkertdev , I've checked the implications against the official docs, and the following are not quite correct:

• there is not any implicit link between the different miscellaneous-extensions features
• only the following implicit links between message-security-assist features exist: MSA8 -> MSA3; MSA9 -> MSA3 & MSA4 ; MSA12 -> MSA6 (but we don't have a MSA6 feature since it doesn't introduce new ISA)
• the MSA7 feature has no HWCAP or STFLE feature bit as it does not provide actual new ISA - it is only an LLVM feature because it provides an additional assembler mnemonic to an already existing instruction

Checking for completeness, for recent processors, the only missing features now are related to privileged (kernel-only) instructions:

  "bear-enhancement" - bit 193
  "reset-dat-protection" - bit 194
  "processor-activity-instrumentation" - bit 196
  "insert-reference-bits-multiple" - bit 145
  "test-pending-external-interruption" - bit 144

It seems OK to omit those (at least until such time as core kernel components may be written in Rust ...).

Every other LLVM feature that is still missing is about rather old processor versions (z13 and older) - at this point in time it's no longer useful to write code distinguishing pre-z13 features, those old machines are barely in use any more (if at all).

Overall, I think with the implicit feature links fixed as described above, this should be good to do. Thanks!

[taiki-e]

Based on that CI log, I believe what is happening is that rust still supportes LLVM 19 (because of linux distributions), and in that version these new target features are not yet present. So, we may need to wait until the lowest supported LLVM version also does support these target features.

Target features not available in older LLVM can be handled in to_llvm_features function in rustc_codegen_llvm/src/llvm_util.rs like some riscv features do:

rust/compiler/rustc_codegen_llvm/src/llvm_util.rs

Lines 275 to 276 in efcbb94

	// Filter out features that are not supported by the current LLVM version
	("riscv32" | "riscv64", "zacas") if get_version().0 < 20 => None,

[uweigand]

This LGTM now from a SystemZ target perspective. Thanks!

[folkertdev]

r? compiler

Thanks Taiki for the quick suggestions and Ulrich for the review as a target maintainer.

[nnethercote]

The approval from @uweigand is helpful from a SystemZ expert, but we should get someone who knows about this stuff on the rustc side (i.e. not me), therefore:

r? @workingjubilee

[workingjubilee]

Every other LLVM feature that is still missing is about rather old processor versions (z13 and older) - at this point in time it's no longer useful to write code distinguishing pre-z13 features, those old machines are barely in use any more (if at all).

Oh, do we have an implicit SystemZ architectural minimum, then? That should probably go in the platform-support docs?

[uweigand]

Every other LLVM feature that is still missing is about rather old processor versions (z13 and older) - at this point in time it's no longer useful to write code distinguishing pre-z13 features, those old machines are barely in use any more (if at all).

Oh, do we have an implicit SystemZ architectural minimum, then? That should probably go in the platform-support docs?

I wouldn't consider it an architectural minimum just yet - that's still z10. We can still generate code that works on anything from z10 upwards. I'm just saying at this point in time it is extremely unlikely that any newly written code would still want to add conditional compilation to make distinctions between older machines like z10, z196, zEC12 etc. Newly written code today would likely want to make such distinctions between z17, z16, z15 or so - so that is where we should provide target feature support primarily.

[workingjubilee]

I'm just saying at this point in time it is extremely unlikely that any newly written code would still want to add conditional compilation to make distinctions between older machines like z10, z196, zEC12 etc.

Ah, that makes sense to me.

[workingjubilee]

cool,
@bors r+ rollup

[bors]

📌 Commit c24e1c3 has been approved by workingjubilee

It is now in the queue for this repository.