Support clobber_abi in MSP430 inline assembly

[taiki-e]

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

Refs: Section 3.2 "Register Conventions" in MSP430 Embedded Application Binary Interface

cc @cr1901

r? @Amanieu

@rustbot label +O-msp430

[cr1901]

Hmmm, I is clobber_abi relatively new? I don't remember it, but I'm also a bit out of practice.

@taiki-e Thanks for providing the relevant section of the manual, so I could refresh. It looks good to me, except for two questions.

• Should clobber_abi also support abi-msp430-interrupt?
  

• Why is this not call void asm sideeffect, and only asm sideeffect?

  // CHECK-LABEL: @clobber_abi
  // CHECK: asm sideeffect "", "={r11},={r12},={r13},={r14},={r15}"()
  #[no_mangle]
  pub unsafe fn clobber_abi() {
      asm!("", clobber_abi("C"), options(nostack, nomem, preserves_flags));
  }
  

[taiki-e]

@cr1901

• Should clobber_abi also support abi-msp430-interrupt?

Thanks for pointing that out, I missed that because it is unstable. However, it appears that *-interrupt ABIs are not currently supported in clobber_abi on other architectures as well. (Since dependence on other unstable features may prevent stabilization, their lack of support is maybe intentional.)

"x86-interrupt",
"avr-interrupt",
"avr-non-blocking-interrupt",
"riscv-interrupt-m",
"riscv-interrupt-s",

x86/x86_64:

rust/compiler/rustc_target/src/asm/mod.rs

Lines 909 to 921 in 3743618

	InlineAsmArch::X86 => match name {
	"C" | "system" | "efiapi" | "cdecl" | "stdcall" | "fastcall" => {
	Ok(InlineAsmClobberAbi::X86)
	}
	_ => Err(&["C", "system", "efiapi", "cdecl", "stdcall", "fastcall"]),
	},
	InlineAsmArch::X86_64 => match name {
	"C" | "system" if !target.is_like_windows => Ok(InlineAsmClobberAbi::X86_64SysV),
	"C" | "system" if target.is_like_windows => Ok(InlineAsmClobberAbi::X86_64Win),
	"win64" | "efiapi" => Ok(InlineAsmClobberAbi::X86_64Win),
	"sysv64" => Ok(InlineAsmClobberAbi::X86_64SysV),
	_ => Err(&["C", "system", "efiapi", "win64", "sysv64"]),
	},

riscv:

rust/compiler/rustc_target/src/asm/mod.rs

Lines 938 to 941 in 3743618

	InlineAsmArch::RiscV32 | InlineAsmArch::RiscV64 => match name {
	"C" | "system" | "efiapi" => Ok(InlineAsmClobberAbi::RiscV),
	_ => Err(&["C", "system", "efiapi"]),
	},

(clobber_abi for AVR is not yet supported)

---

• Why is this not call void asm sideeffect, and only asm sideeffect?

This is because it is not a call void asm, but a very long one: call { i16, i16, i16, i16, i16 } asm

That test is based on the same test for s390x added in #130630, and call ... asm for s390x was call { i32, i32, i32, i32, i32, i32, i32, double, double, double, double, double, double, double, double } asm.
In #130630, I had originally intended to write everything call ..., but realized it would be too long for clobber_abi and omitted it. I left it at the other ones (flags and clobber-only registers) because I thought if they were not call void asm, something was wrong.

FYI, for x86_64, it is call { i32, i32, i32, i32, i32, i32, i32, i32, i32, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float, float } asm,
and call ... asm sideeffect "", is omitted in codegen test for clobber_abi:

rust/tests/codegen/asm-clobber_abi.rs

Line 9 in 3743618

// CHECK: ={ax},={cx},={dx},={si},={di},={r8},={r9},={r10},={r11},={xmm0},={xmm1},={xmm2},={xmm3},={xmm4},={xmm5},={xmm6},={xmm7},={xmm8},={xmm9},={xmm10},={xmm11},={xmm12},={xmm13},={xmm14},={xmm15},~{xmm16},~{xmm17},~{xmm18},~{xmm19},~{xmm20},~{xmm21},~{xmm22},~{xmm23},~{xmm24},~{xmm25},~{xmm26},~{xmm27},~{xmm28},~{xmm29},~{xmm30},~{xmm31},~{k0},~{k1},~{k2},~{k3},~{k4},~{k5},~{k6},~{k7},~{st},~{st(1)},~{st(2)},~{st(3)},~{st(4)},~{st(5)},~{st(6)},~{st(7)},~{tmm0},~{tmm1},~{tmm2},~{tmm3},~{tmm4},~{tmm5},~{tmm6},~{tmm7},~{dirflag},~{fpsr},~{flags},~{memory}

[cr1901]

Since dependence on other unstable features may prevent stabilization, their lack of support is maybe intentional.

That's fair. AFAIK no one is driving the current RFC for unified interrupt calling conventions forward, so perhaps no impetus to support the interrupt calling conventions elsewhere right now.

This is because it is not a call void asm, but a very long one: call { i16, i16, i16, i16, i16 } asm

Ahhh okay I see, CHECK strings need not match at the beginning. I've only ever written "full" CHECK strings.

This PR looks fine to me.

[Amanieu]

Interrupt calling conventions can't be supported by clobber_abi because they clobber reserved registers, which is not supported by back-ends.

[Amanieu]

@bors r+

[bors]

📌 Commit 3743618 has been approved by Amanieu

It is now in the queue for this repository.