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stabilize s390x vector registers #2215

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stabilize s390x vector registers #2215

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8 changes: 6 additions & 2 deletions src/inline-assembly.md
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Expand Up @@ -318,6 +318,9 @@ unsafe { core::arch::asm!("/* {} */", in(reg) 5); }
# }
```

> [!NOTE]
> If the value's type is smaller than the register, the value of the upper bits is platform-specific. Some targets zero out the upper bits, while others leave them untouched.
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@folkertdev folkertdev Mar 22, 2026

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This came up in the stabilization PR. Amanieu mentions that aarch64 zeros the upper bits, while s390x does not touch them.

This might need some re-phrasing, but I think it's useful to include to prevent future confusion.


r[asm.operand-type.supported-operands.out]
* `out(<reg>) <expr>`
- `<reg>` can refer to a register class or an explicit register. The allocated register name is substituted into the asm template string.
Expand Down Expand Up @@ -626,7 +629,7 @@ Here is the list of currently supported register classes:
| s390x | `reg` | `r[0-10]`, `r[12-14]` | `r` |
| s390x | `reg_addr` | `r[1-10]`, `r[12-14]` | `a` |
| s390x | `freg` | `f[0-15]` | `f` |
| s390x | `vreg` | `v[0-31]` | Only clobbers |
| s390x | `vreg` | `v[0-31]` | `v` |
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@folkertdev folkertdev Mar 22, 2026

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e.g. in https://godbolt.org/z/vxeWTe5KG

| s390x | `areg` | `a[2-15]` | Only clobbers |
| PowerPC | `reg` | `r0`, `r[3-12]`, `r[14-28]` | `r` |
| PowerPC | `reg_nonzero` | `r[3-12]`, `r[14-28]` | `b` |
Expand Down Expand Up @@ -683,7 +686,7 @@ Each register class has constraints on which value types they can be used with.
| LoongArch | `freg` | `d` | `f64` |
| s390x | `reg`, `reg_addr` | None | `i8`, `i16`, `i32`, `i64` |
| s390x | `freg` | None | `f32`, `f64` |
| s390x | `vreg` | N/A | Only clobbers |
| s390x | `vreg` | `vector` | `i32`, `f32`, `i64`, `f64`, `i128`, <br> `i8x16`, `i16x8`, `i32x4`, `i64x2`, `f32x4`, `f64x2` |
| s390x | `areg` | N/A | Only clobbers |
| PowerPC | `spe_acc` | None | Only clobbers |
| PowerPC/PowerPC64 | `reg` | None | `i8`, `i16`, `i32`, `i64` (PowerPC64 only) |
Expand Down Expand Up @@ -945,6 +948,7 @@ The supported modifiers are a subset of LLVM's (and GCC's) [asm template argumen
| s390x | `reg` | None | `%r0` | None |
| s390x | `reg_addr` | None | `%r1` | None |
| s390x | `freg` | None | `%f0` | None |
| s390x | `vreg` | None | `%v0` | None |
| PowerPC/PowerPC64 | `reg` | None | `0` | None |
| PowerPC/PowerPC64 | `reg_nonzero` | None | `3` | None |
| PowerPC/PowerPC64 | `freg` | None | `0` | None |
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