Rollup merge of #131664 - taiki-e:s390x-asm-vreg-inout, r=Amanieu

Support input/output in vector registers of s390x inline assembly (under asm_experimental_reg feature)

This extends currently clobber-only vector registers (`vreg`) support to allow passing `#[repr(simd)]` types, floats (f32/f64/f128), and integers (i32/i64/i128) as input/output.

This is unstable and gated under new `#![feature(asm_experimental_reg)]` (tracking issue: https://github.com/rust-lang/rust/issues/133416). If the feature is not enabled, only clober is supported as before.

| Architecture | Register class | Target feature | Allowed types |
| ------------ | -------------- | -------------- | -------------- |
| s390x | `vreg` | `vector` | `i32`, `f32`, `i64`, `f64`, `i128`, `f128`, `i8x16`, `i16x8`, `i32x4`, `i64x2`, `f32x4`, `f64x2` |

This matches the list of types that are supported by the vector registers in LLVM:
https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZRegisterInfo.td#L301-L313

In addition to `core::simd` types and floats listed above, custom `#[repr(simd)]` types of the same size and type are also allowed. All allowed types other than i32/f32/i64/f64/i128, and relevant target features are currently unstable.

Currently there is no SIMD type for s390x in `core::arch`, but this is tracked in https://github.com/rust-lang/rust/issues/130869.

cc https://github.com/rust-lang/rust/issues/130869 about vector facility support in s390x
cc https://github.com/rust-lang/rust/issues/125398 & https://github.com/rust-lang/rust/issues/116909 about f128 support in asm

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

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index e6a3f939f2d..447af57354f 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -280,6 +280,14 @@ pub(crate) struct RegisterClassOnlyClobber {
 }
 
 #[derive(Diagnostic)]
+#[diag(ast_lowering_register_class_only_clobber_stable)]
+pub(crate) struct RegisterClassOnlyClobberStable {
+    #[primary_span]
+    pub op_span: Span,
+    pub reg_class_name: Symbol,
+}
+
+#[derive(Diagnostic)]
 #[diag(ast_lowering_register_conflict)]
 pub(crate) struct RegisterConflict<'a> {
     #[primary_span]