Rollup merge of #111331 - taiki-e:s390x-asm-cc, r=Amanieu

Mark s390x condition code register as clobbered in inline assembly

Various s390x instructions (arithmetic operations, logical operations, comparisons, etc. see also "Condition Codes" section in [z/Architecture Reference Summary](https://www.ibm.com/support/pages/zarchitecture-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`

compiler/rustc_codegen_llvm/src/asm.rs

@@ -238,7 +238,9 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                 InlineAsmArch::Hexagon => {}
                 InlineAsmArch::LoongArch64 => {}
                 InlineAsmArch::Mips | InlineAsmArch::Mips64 => {}
-                InlineAsmArch::S390x => {}
+                InlineAsmArch::S390x => {
+                    constraints.push("~{cc}".to_string());
+                }
                 InlineAsmArch::SpirV => {}
                 InlineAsmArch::Wasm32 | InlineAsmArch::Wasm64 => {}
                 InlineAsmArch::Bpf => {}

src/doc/unstable-book/src/language-features/asm-experimental-arch.md

@@ -18,6 +18,7 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 - MSP430
 - M68k
 - LoongArch
+- s390x
 
 ## Register classes
 
@@ -48,6 +49,8 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 | M68k         | `reg_addr`     | `a[0-3]`                           | `a`                  |
 | LoongArch    | `reg`          | `$r1`, `$r[4-20]`, `$r[23,30]`     | `r`                  |
 | LoongArch    | `freg`         | `$f[0-31]`                         | `f`                  |
+| s390x        | `reg`          | `r[0-10]`, `r[12-14]`              | `r`                  |
+| s390x        | `freg`         | `f[0-15]`                          | `f`                  |
 
 > **Notes**:
 > - NVPTX doesn't have a fixed register set, so named registers are not supported.
@@ -81,6 +84,8 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 | M68k         | `reg_data`                      | None           | `i8`, `i16`, `i32`                      |
 | LoongArch64  | `reg`                           | None           | `i8`, `i16`, `i32`, `i64`, `f32`, `f64` |
 | LoongArch64  | `freg`                          | None           | `f32`, `f64`                            |
+| s390x        | `reg`                           | None           | `i8`, `i16`, `i32`, `i64`               |
+| s390x        | `freg`                          | None           | `f32`, `f64`                            |
 
 ## Register aliases
 
@@ -115,8 +120,8 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 
 | Architecture | Unsupported register                    | Reason                                                                                                                                                                              |
 | ------------ | --------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| All          | `sp`                                    | The stack pointer must be restored to its original value at the end of an asm code block.                                                                                           |
-| All          | `fr` (Hexagon), `$fp` (MIPS), `Y` (AVR), `r4` (MSP430), `a6` (M68k), `$fp` (LoongArch) | The frame pointer cannot be used as an input or output.                                                                                                                             |
+| All          | `sp`, `r15` (s390x)                     | The stack pointer must be restored to its original value at the end of an asm code block.                                                                                           |
+| All          | `fr` (Hexagon), `$fp` (MIPS), `Y` (AVR), `r4` (MSP430), `a6` (M68k), `$fp` (LoongArch), `r11` (s390x) | The frame pointer cannot be used as an input or output.                                                                                                                             |
 | All          | `r19` (Hexagon)                         | This is used internally by LLVM as a "base pointer" for functions with complex stack frames.                                                                                        |
 | MIPS         | `$0` or `$zero`                         | This is a constant zero register which can't be modified.                                                                                                                           |
 | MIPS         | `$1` or `$at`                           | Reserved for assembler.                                                                                                                                                             |
@@ -147,6 +152,8 @@ This feature tracks `asm!` and `global_asm!` support for the following architect
 | PowerPC      | `freg`         | None     | `0`            | None          |
 | LoongArch    | `reg`          | None     | `$r2`          | None          |
 | LoongArch    | `freg`         | None     | `$f0`          | None          |
+| s390x        | `reg`          | None     | `%r0`          | None          |
+| s390x        | `freg`         | None     | `%f0`          | None          |
 
 # Flags covered by `preserves_flags`
 
@@ -157,3 +164,5 @@ These flags registers must be restored upon exiting the asm block if the `preser
   - The status register `r2`.
 - M68k
   - The condition code register `ccr`.
+- s390x
+  - The condition code register `cc`.