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Mark s390x condition code register as clobbered in inline assembly #111331

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merged 1 commit into from
May 8, 2023

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@taiki-e taiki-e commented May 8, 2023

Various s390x instructions (arithmetic operations, logical operations, comparisons, etc. see also "Condition Codes" section in z/Architecture Reference Summary) modify condition code register cc, but AFAIK there is currently no way to mark it as clobbered in asm!.

cc register definition in LLVM:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L320

This PR also updates asm_experimental_arch docs in the unstable-book to mention s390x registers.

cc @uweigand

r? @Amanieu

@rustbot label +O-SystemZ +A-inline-assembly

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 8, 2023
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Amanieu commented May 8, 2023

Not directly related to this PR, but for clobber_abi support we'll probably need a way to mark the access registers as clobbered since they are volatile according to the calling convention.

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Amanieu commented May 8, 2023

@bors r+

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bors commented May 8, 2023

📌 Commit e61bb88 has been approved by Amanieu

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 8, 2023
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uweigand commented May 8, 2023

This looks correct to me. Thanks for taking care of this!

bors added a commit to rust-lang-ci/rust that referenced this pull request May 8, 2023
Rollup of 7 pull requests

Successful merges:

 - rust-lang#105354 (Add deployment-target --print flag for Apple targets)
 - rust-lang#110377 (Update max_atomic_width of armv7r and armv7_sony_vita targets to 64.)
 - rust-lang#110638 (STD support for PSVita)
 - rust-lang#111211 (Don't compute trait super bounds unless they're positive)
 - rust-lang#111315 (Remove `identity_future` from stdlib)
 - rust-lang#111331 (Mark s390x condition code register as clobbered in inline assembly)
 - rust-lang#111332 (Improve inline asm for LoongArch)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit c122ac3 into rust-lang:master May 8, 2023
@rustbot rustbot added this to the 1.71.0 milestone May 8, 2023
@taiki-e taiki-e deleted the s390x-asm-cc branch May 8, 2023 14:27
@rustbot rustbot added the O-SystemZ Target: SystemZ processors (s390x) label Sep 20, 2024
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this pull request Oct 1, 2024
Support clobber_abi and vector/access registers (clobber-only) in s390x inline assembly

This supports `clobber_abi` which is one of the requirements of stabilization mentioned in rust-lang#93335.

This also supports vector registers (as `vreg`) and access registers (as `areg`) as clobber-only, which need to support clobbering of them to implement clobber_abi.

Refs:
- "1.2.1.1. Register Preservation Rules" section 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)
- Register definition in LLVM:
  - Vector registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L249
  - Access registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L332

I have three questions:
- ~~ELF Application Binary Interface s390x Supplement says that `cc` (condition code, bits 18-19 of PSW) is "Volatile".
  However, we do not have a register class for `cc` and instead mark `cc` as clobbered unless `preserves_flags` is specified (rust-lang#111331).
  Therefore, in the current implementation, if both `preserves_flags` and `clobber_abi` are specified, `cc` is not marked as clobbered. Is this okay? Or even if `preserves_flags` is used, should `cc` be marked as clobbered if `clobber_abi` is used?~~ UPDATE: resolved rust-lang#130630 (comment)
- ~~ELF Application Binary Interface s390x Supplement says that `pm` (program mask, bits 20-23 of PSW) is "Cleared".
  There does not appear to be any registers associated with this in either [LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td) or [GCC](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L407-L431), so at this point I don't see any way other than to just ignore it. Is this okay as-is?~~ UPDATE: resolved rust-lang#130630 (comment)
- Is "areg" a good name for register class name for access registers? It may be a bit confusing between that and `reg_addr`, which uses the “a” constraint (rust-lang#119431)...

Note:

- GCC seems to [recognize only `a0` and `a1`](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L428-L429), and using `a[2-15]` [causes errors](https://godbolt.org/z/a46vx8jjn).
  Given that cg_gcc has a similar problem with other architecture (rust-lang/rustc_codegen_gcc#485), I don't feel this is a blocker for this PR, but it is worth mentioning here.
- `vreg` should be able to accept `#[repr(simd)]` types as input if the `vector` target feature added in rust-lang#127506 is enabled, but core_arch has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable, so I have not implemented it in this PR. EDIT: And supporting it is probably more complex than doing the equivalent on other architectures... rust-lang#88245 (comment)

cc `@uweigand`

r? `@Amanieu`

`@rustbot` label +O-SystemZ
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Oct 1, 2024
Rollup merge of rust-lang#130630 - taiki-e:s390x-clobber-abi, r=Amanieu

Support clobber_abi and vector/access registers (clobber-only) in s390x inline assembly

This supports `clobber_abi` which is one of the requirements of stabilization mentioned in rust-lang#93335.

This also supports vector registers (as `vreg`) and access registers (as `areg`) as clobber-only, which need to support clobbering of them to implement clobber_abi.

Refs:
- "1.2.1.1. Register Preservation Rules" section 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)
- Register definition in LLVM:
  - Vector registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L249
  - Access registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L332

I have three questions:
- ~~ELF Application Binary Interface s390x Supplement says that `cc` (condition code, bits 18-19 of PSW) is "Volatile".
  However, we do not have a register class for `cc` and instead mark `cc` as clobbered unless `preserves_flags` is specified (rust-lang#111331).
  Therefore, in the current implementation, if both `preserves_flags` and `clobber_abi` are specified, `cc` is not marked as clobbered. Is this okay? Or even if `preserves_flags` is used, should `cc` be marked as clobbered if `clobber_abi` is used?~~ UPDATE: resolved rust-lang#130630 (comment)
- ~~ELF Application Binary Interface s390x Supplement says that `pm` (program mask, bits 20-23 of PSW) is "Cleared".
  There does not appear to be any registers associated with this in either [LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td) or [GCC](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L407-L431), so at this point I don't see any way other than to just ignore it. Is this okay as-is?~~ UPDATE: resolved rust-lang#130630 (comment)
- Is "areg" a good name for register class name for access registers? It may be a bit confusing between that and `reg_addr`, which uses the “a” constraint (rust-lang#119431)...

Note:

- GCC seems to [recognize only `a0` and `a1`](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L428-L429), and using `a[2-15]` [causes errors](https://godbolt.org/z/a46vx8jjn).
  Given that cg_gcc has a similar problem with other architecture (rust-lang/rustc_codegen_gcc#485), I don't feel this is a blocker for this PR, but it is worth mentioning here.
- `vreg` should be able to accept `#[repr(simd)]` types as input if the `vector` target feature added in rust-lang#127506 is enabled, but core_arch has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable, so I have not implemented it in this PR. EDIT: And supporting it is probably more complex than doing the equivalent on other architectures... rust-lang#88245 (comment)

cc `@uweigand`

r? `@Amanieu`

`@rustbot` label +O-SystemZ
antoyo pushed a commit to rust-lang/rustc_codegen_gcc that referenced this pull request Oct 9, 2024
Support clobber_abi and vector/access registers (clobber-only) in s390x inline assembly

This supports `clobber_abi` which is one of the requirements of stabilization mentioned in #93335.

This also supports vector registers (as `vreg`) and access registers (as `areg`) as clobber-only, which need to support clobbering of them to implement clobber_abi.

Refs:
- "1.2.1.1. Register Preservation Rules" section 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)
- Register definition in LLVM:
  - Vector registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L249
  - Access registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L332

I have three questions:
- ~~ELF Application Binary Interface s390x Supplement says that `cc` (condition code, bits 18-19 of PSW) is "Volatile".
  However, we do not have a register class for `cc` and instead mark `cc` as clobbered unless `preserves_flags` is specified (rust-lang/rust#111331).
  Therefore, in the current implementation, if both `preserves_flags` and `clobber_abi` are specified, `cc` is not marked as clobbered. Is this okay? Or even if `preserves_flags` is used, should `cc` be marked as clobbered if `clobber_abi` is used?~~ UPDATE: resolved rust-lang/rust#130630 (comment)
- ~~ELF Application Binary Interface s390x Supplement says that `pm` (program mask, bits 20-23 of PSW) is "Cleared".
  There does not appear to be any registers associated with this in either [LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td) or [GCC](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L407-L431), so at this point I don't see any way other than to just ignore it. Is this okay as-is?~~ UPDATE: resolved rust-lang/rust#130630 (comment)
- Is "areg" a good name for register class name for access registers? It may be a bit confusing between that and `reg_addr`, which uses the “a” constraint (rust-lang/rust#119431)...

Note:

- GCC seems to [recognize only `a0` and `a1`](https://github.com/gcc-mirror/gcc/blob/33ccc1314dcdb0b988a9276ca6b6ce9b07bea21e/gcc/config/s390/s390.h#L428-L429), and using `a[2-15]` [causes errors](https://godbolt.org/z/a46vx8jjn).
  Given that cg_gcc has a similar problem with other architecture (#485), I don't feel this is a blocker for this PR, but it is worth mentioning here.
- `vreg` should be able to accept `#[repr(simd)]` types as input if the `vector` target feature added in rust-lang/rust#127506 is enabled, but core_arch has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable, so I have not implemented it in this PR. EDIT: And supporting it is probably more complex than doing the equivalent on other architectures... rust-lang/rust#88245 (comment)

cc `@uweigand`

r? `@Amanieu`

`@rustbot` label +O-SystemZ
@rustbot rustbot added the A-inline-assembly Area: Inline assembly (`asm!(…)`) label Oct 13, 2024
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Nov 9, 2024
…nieu

Stabilize s390x inline assembly

This stabilizes inline assembly for s390x (SystemZ).

Corresponding reference PR: rust-lang/reference#1643

---

From the requirements of stabilization mentioned in rust-lang#93335

> Each architecture needs to be reviewed before stabilization:

> - It must have clobber_abi.

Done in rust-lang#130630.

> - It must be possible to clobber every register that is normally clobbered by a function call.

Done in the PR that added support for clobber_abi.

> - Generally review that the exposed register classes make sense.

The followings can be used as input/output:

- `reg` (`r[0-10]`, `r[12-14]`): General-purpose register

- `reg_addr` (`r[1-10]`, `r[12-14]`): General-purpose register except `r0` which is evaluated as zero in an address context

  This class is needed because `r0`, which may be allocated when using the `reg` class, cannot be used as a register in certain contexts. This is identical to the `a` constraint in LLVM and GCC. See rust-lang#119431 for details.

- `freg` (`f[0-15]`): Floating-point register

The followings are clobber-only:

- `vreg` (`v[0-31]`): Vector register

  Technically `vreg` should be able to accept `#[repr(simd)]` types as input/output if the unstable `vector` target feature added is enabled, but `core::arch` has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable. Everything related is unstable, so the fact that this is currently a clobber-only should not be considered a stabilization blocker. (rust-lang#130869 tracks unstable stuff here)

- `areg` (`a[2-15]`): Access register

All of the above register classes except `reg_addr` are needed for `clobber_abi`.

The followings cannot be used as operands for inline asm (see also [getReservedRegs](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.cpp#L258-L282) and [SystemZELFRegisters](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.h#L107-L128) in LLVM):

- `r11`: frame pointer
- `r15`: stack pointer
- `a0`, `a1`: Reserved for system use
- `c[0-15]` (control register)  Reserved by the kernel

Although not listed in the above requirements, `preserves_flags` is implemented in rust-lang#111331.

---

cc `@uweigand`

r? `@Amanieu`

`@rustbot` label +O-SystemZ +A-inline-assembly
workingjubilee added a commit to workingjubilee/rustc that referenced this pull request Nov 10, 2024
…nieu

Stabilize s390x inline assembly

This stabilizes inline assembly for s390x (SystemZ).

Corresponding reference PR: rust-lang/reference#1643

---

From the requirements of stabilization mentioned in rust-lang#93335

> Each architecture needs to be reviewed before stabilization:

> - It must have clobber_abi.

Done in rust-lang#130630.

> - It must be possible to clobber every register that is normally clobbered by a function call.

Done in the PR that added support for clobber_abi.

> - Generally review that the exposed register classes make sense.

The followings can be used as input/output:

- `reg` (`r[0-10]`, `r[12-14]`): General-purpose register

- `reg_addr` (`r[1-10]`, `r[12-14]`): General-purpose register except `r0` which is evaluated as zero in an address context

  This class is needed because `r0`, which may be allocated when using the `reg` class, cannot be used as a register in certain contexts. This is identical to the `a` constraint in LLVM and GCC. See rust-lang#119431 for details.

- `freg` (`f[0-15]`): Floating-point register

The followings are clobber-only:

- `vreg` (`v[0-31]`): Vector register

  Technically `vreg` should be able to accept `#[repr(simd)]` types as input/output if the unstable `vector` target feature added is enabled, but `core::arch` has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable. Everything related is unstable, so the fact that this is currently a clobber-only should not be considered a stabilization blocker. (rust-lang#130869 tracks unstable stuff here)

- `areg` (`a[2-15]`): Access register

All of the above register classes except `reg_addr` are needed for `clobber_abi`.

The followings cannot be used as operands for inline asm (see also [getReservedRegs](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.cpp#L258-L282) and [SystemZELFRegisters](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.h#L107-L128) in LLVM):

- `r11`: frame pointer
- `r15`: stack pointer
- `a0`, `a1`: Reserved for system use
- `c[0-15]` (control register)  Reserved by the kernel

Although not listed in the above requirements, `preserves_flags` is implemented in rust-lang#111331.

---

cc ``@uweigand``

r? ``@Amanieu``

``@rustbot`` label +O-SystemZ +A-inline-assembly
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Nov 10, 2024
Rollup merge of rust-lang#131258 - taiki-e:s390x-stabilize-asm, r=Amanieu

Stabilize s390x inline assembly

This stabilizes inline assembly for s390x (SystemZ).

Corresponding reference PR: rust-lang/reference#1643

---

From the requirements of stabilization mentioned in rust-lang#93335

> Each architecture needs to be reviewed before stabilization:

> - It must have clobber_abi.

Done in rust-lang#130630.

> - It must be possible to clobber every register that is normally clobbered by a function call.

Done in the PR that added support for clobber_abi.

> - Generally review that the exposed register classes make sense.

The followings can be used as input/output:

- `reg` (`r[0-10]`, `r[12-14]`): General-purpose register

- `reg_addr` (`r[1-10]`, `r[12-14]`): General-purpose register except `r0` which is evaluated as zero in an address context

  This class is needed because `r0`, which may be allocated when using the `reg` class, cannot be used as a register in certain contexts. This is identical to the `a` constraint in LLVM and GCC. See rust-lang#119431 for details.

- `freg` (`f[0-15]`): Floating-point register

The followings are clobber-only:

- `vreg` (`v[0-31]`): Vector register

  Technically `vreg` should be able to accept `#[repr(simd)]` types as input/output if the unstable `vector` target feature added is enabled, but `core::arch` has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable. Everything related is unstable, so the fact that this is currently a clobber-only should not be considered a stabilization blocker. (rust-lang#130869 tracks unstable stuff here)

- `areg` (`a[2-15]`): Access register

All of the above register classes except `reg_addr` are needed for `clobber_abi`.

The followings cannot be used as operands for inline asm (see also [getReservedRegs](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.cpp#L258-L282) and [SystemZELFRegisters](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.h#L107-L128) in LLVM):

- `r11`: frame pointer
- `r15`: stack pointer
- `a0`, `a1`: Reserved for system use
- `c[0-15]` (control register)  Reserved by the kernel

Although not listed in the above requirements, `preserves_flags` is implemented in rust-lang#111331.

---

cc ``@uweigand``

r? ``@Amanieu``

``@rustbot`` label +O-SystemZ +A-inline-assembly
RalfJung pushed a commit to RalfJung/miri that referenced this pull request Nov 10, 2024
Stabilize s390x inline assembly

This stabilizes inline assembly for s390x (SystemZ).

Corresponding reference PR: rust-lang/reference#1643

---

From the requirements of stabilization mentioned in rust-lang/rust#93335

> Each architecture needs to be reviewed before stabilization:

> - It must have clobber_abi.

Done in rust-lang/rust#130630.

> - It must be possible to clobber every register that is normally clobbered by a function call.

Done in the PR that added support for clobber_abi.

> - Generally review that the exposed register classes make sense.

The followings can be used as input/output:

- `reg` (`r[0-10]`, `r[12-14]`): General-purpose register

- `reg_addr` (`r[1-10]`, `r[12-14]`): General-purpose register except `r0` which is evaluated as zero in an address context

  This class is needed because `r0`, which may be allocated when using the `reg` class, cannot be used as a register in certain contexts. This is identical to the `a` constraint in LLVM and GCC. See rust-lang/rust#119431 for details.

- `freg` (`f[0-15]`): Floating-point register

The followings are clobber-only:

- `vreg` (`v[0-31]`): Vector register

  Technically `vreg` should be able to accept `#[repr(simd)]` types as input/output if the unstable `vector` target feature added is enabled, but `core::arch` has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable. Everything related is unstable, so the fact that this is currently a clobber-only should not be considered a stabilization blocker. (rust-lang/rust#130869 tracks unstable stuff here)

- `areg` (`a[2-15]`): Access register

All of the above register classes except `reg_addr` are needed for `clobber_abi`.

The followings cannot be used as operands for inline asm (see also [getReservedRegs](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.cpp#L258-L282) and [SystemZELFRegisters](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.h#L107-L128) in LLVM):

- `r11`: frame pointer
- `r15`: stack pointer
- `a0`, `a1`: Reserved for system use
- `c[0-15]` (control register)  Reserved by the kernel

Although not listed in the above requirements, `preserves_flags` is implemented in rust-lang/rust#111331.

---

cc ``@uweigand``

r? ``@Amanieu``

``@rustbot`` label +O-SystemZ +A-inline-assembly
mati865 pushed a commit to mati865/rust that referenced this pull request Nov 12, 2024
…nieu

Stabilize s390x inline assembly

This stabilizes inline assembly for s390x (SystemZ).

Corresponding reference PR: rust-lang/reference#1643

---

From the requirements of stabilization mentioned in rust-lang#93335

> Each architecture needs to be reviewed before stabilization:

> - It must have clobber_abi.

Done in rust-lang#130630.

> - It must be possible to clobber every register that is normally clobbered by a function call.

Done in the PR that added support for clobber_abi.

> - Generally review that the exposed register classes make sense.

The followings can be used as input/output:

- `reg` (`r[0-10]`, `r[12-14]`): General-purpose register

- `reg_addr` (`r[1-10]`, `r[12-14]`): General-purpose register except `r0` which is evaluated as zero in an address context

  This class is needed because `r0`, which may be allocated when using the `reg` class, cannot be used as a register in certain contexts. This is identical to the `a` constraint in LLVM and GCC. See rust-lang#119431 for details.

- `freg` (`f[0-15]`): Floating-point register

The followings are clobber-only:

- `vreg` (`v[0-31]`): Vector register

  Technically `vreg` should be able to accept `#[repr(simd)]` types as input/output if the unstable `vector` target feature added is enabled, but `core::arch` has no s390x vector type and both `#[repr(simd)]` and `core::simd` are unstable. Everything related is unstable, so the fact that this is currently a clobber-only should not be considered a stabilization blocker. (rust-lang#130869 tracks unstable stuff here)

- `areg` (`a[2-15]`): Access register

All of the above register classes except `reg_addr` are needed for `clobber_abi`.

The followings cannot be used as operands for inline asm (see also [getReservedRegs](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.cpp#L258-L282) and [SystemZELFRegisters](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.h#L107-L128) in LLVM):

- `r11`: frame pointer
- `r15`: stack pointer
- `a0`, `a1`: Reserved for system use
- `c[0-15]` (control register)  Reserved by the kernel

Although not listed in the above requirements, `preserves_flags` is implemented in rust-lang#111331.

---

cc ``@uweigand``

r? ``@Amanieu``

``@rustbot`` label +O-SystemZ +A-inline-assembly
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A-inline-assembly Area: Inline assembly (`asm!(…)`) O-SystemZ Target: SystemZ processors (s390x) S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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