Rollup merge of rust-lang#144379 - folkertdev:c-variadic-same-program-multiple-abis, r=RalfJung

test using multiple c-variadic ABIs in the same program

tracking issue: rust-lang#100189

Check that multiple c-variadic calling conventions can be used in the same program.

Clang and gcc reject defining functions with a non-default calling convention and a variable
argument list, so C programs that use multiple c-variadic calling conventions are unlikely
to come up. Here we validate that our codegen backends do in fact generate correct code.

(CI will not run this test because it runs on aarch64, I would like to at least test that this runs on windows)

try-job: `x86_64-gnu`
try-job: `x86_64-msvc-*`

Author: GuillaumeGomez

tests/ui/c-variadic/same-program-multiple-abis.rs

@@ -0,0 +1,110 @@
+#![feature(extended_varargs_abi_support)]
+//@ run-pass
+//@ only-x86_64
+
+// Check that multiple c-variadic calling conventions can be used in the same program.
+//
+// Clang and gcc reject defining functions with a non-default calling convention and a variable
+// argument list, so C programs that use multiple c-variadic calling conventions are unlikely
+// to come up. Here we validate that our codegen backends do in fact generate correct code.
+
+extern "sysv64" {
+    fn variadic_sysv64(_: u32, _: ...) -> u32;
+}
+
+extern "win64" {
+    fn variadic_win64(_: u32, _: ...) -> u32;
+}
+
+fn main() {
+    unsafe {
+        assert_eq!(variadic_win64(1, 2, 3), 1 + 2 + 3);
+        assert_eq!(variadic_sysv64(1, 2, 3), 1 + 2 + 3);
+    }
+}
+
+// This assembly was generated using https://godbolt.org/z/dbTGanoh6, and corresponds to the
+// following code compiled for the `x86_64-unknown-linux-gnu` and `x86_64-pc-windows-gnu`
+// targets, respectively:
+//
+// ```rust
+// #![feature(c_variadic)]
+//
+// #[unsafe(no_mangle)]
+// unsafe extern "C" fn variadic(a: u32, mut args: ...) -> u32 {
+//     let b = args.arg::<u32>();
+//     let c = args.arg::<u32>();
+//
+//     a + b + c
+// }
+// ```
+core::arch::global_asm!(
+    r#"
+variadic_sysv64:
+        sub     rsp, 88
+        test    al, al
+        je      .LBB0_7
+        movaps  xmmword ptr [rsp - 48], xmm0
+        movaps  xmmword ptr [rsp - 32], xmm1
+        movaps  xmmword ptr [rsp - 16], xmm2
+        movaps  xmmword ptr [rsp], xmm3
+        movaps  xmmword ptr [rsp + 16], xmm4
+        movaps  xmmword ptr [rsp + 32], xmm5
+        movaps  xmmword ptr [rsp + 48], xmm6
+        movaps  xmmword ptr [rsp + 64], xmm7
+.LBB0_7:
+        mov     qword ptr [rsp - 88], rsi
+        mov     qword ptr [rsp - 80], rdx
+        mov     qword ptr [rsp - 72], rcx
+        mov     qword ptr [rsp - 64], r8
+        mov     qword ptr [rsp - 56], r9
+        movabs  rax, 206158430216
+        mov     qword ptr [rsp - 120], rax
+        lea     rax, [rsp + 96]
+        mov     qword ptr [rsp - 112], rax
+        lea     rax, [rsp - 96]
+        mov     qword ptr [rsp - 104], rax
+        mov     edx, 8
+        cmp     rdx, 41
+        jae     .LBB0_1
+        mov     rax, qword ptr [rsp - 104]
+        mov     ecx, 8
+        add     rcx, 8
+        mov     dword ptr [rsp - 120], ecx
+        mov     eax, dword ptr [rax + rdx]
+        cmp     edx, 32
+        ja      .LBB0_2
+        add     rcx, qword ptr [rsp - 104]
+        add     edx, 16
+        mov     dword ptr [rsp - 120], edx
+        add     eax, edi
+        add     eax, dword ptr [rcx]
+        add     rsp, 88
+        ret
+.LBB0_1:
+        mov     rax, qword ptr [rsp - 112]
+        lea     rcx, [rax + 8]
+        mov     qword ptr [rsp - 112], rcx
+        mov     eax, dword ptr [rax]
+.LBB0_2:
+        mov     rcx, qword ptr [rsp - 112]
+        lea     rdx, [rcx + 8]
+        mov     qword ptr [rsp - 112], rdx
+        add     eax, edi
+        add     eax, dword ptr [rcx]
+        add     rsp, 88
+        ret
+
+variadic_win64:
+        push    rax
+        mov     qword ptr [rsp + 40], r9
+        mov     qword ptr [rsp + 24], rdx
+        mov     qword ptr [rsp + 32], r8
+        lea     rax, [rsp + 40]
+        mov     qword ptr [rsp], rax
+        lea     eax, [rdx + rcx]
+        add     eax, r8d
+        pop     rcx
+        ret
+    "#
+);