Unrolled build for #165467 in rollup 165510

Rollup merge of #165467 - beetrees:va-arg-msp430, r=folkertdev

Use `emit_ptr_va_arg` for `va_arg` on MSP430

This avoids needing to use the LLVM `va_arg` instruction. The implementation matches LLVM and GCC (checked by comparing the assembly), with the exception that GCC doesn't seem to align the `va_list` pointer before a `va_arg(va, void*)` - AFAICT this is a GCC bug as GCC does align pointers when passing them to C-variadic functions. This PR always correctly aligns the pointer, matching LLVM and the spec.

cc @cr1901

r? @folkertdev

Author: bors

compiler/rustc_codegen_llvm/src/va_arg.rs

@@ -1295,11 +1295,20 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
                 Endian::Little => ForceRightAdjust::No,
             },
         ),
+        Arch::Msp430 => emit_ptr_va_arg(
+            bx,
+            addr,
+            layout,
+            PassMode::Direct,
+            SlotSize::Bytes1,
+            AllowHigherAlign::Yes,
+            ForceRightAdjust::No,
+        ),
 
         Arch::Bpf => bug!("bpf does not support c-variadic functions"),
         Arch::SpirV => bug!("spirv does not support c-variadic functions"),
 
-        Arch::Avr | Arch::M68k | Arch::Msp430 => {
+        Arch::Avr | Arch::M68k => {
             std::assert_matches!(stability, CVariadicStatus::Unstable { .. });
 
             // Clang uses the LLVM implementation for these architectures.

tests/assembly-llvm/c-variadic/msp430.rs

@@ -0,0 +1,85 @@
+//@ add-minicore
+//@ assembly-output: emit-asm
+//
+//@ compile-flags: -Copt-level=3 --target=msp430-none-elf
+//@ needs-llvm-components: msp430
+#![feature(c_variadic_experimental_arch, no_core, lang_items, intrinsics, rustc_attrs)]
+#![no_core]
+#![crate_type = "lib"]
+
+extern crate minicore;
+use minicore::ffi::VaList;
+use minicore::*;
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn read_f64(ap: &mut VaList<'_>) -> f64 {
+    // CHECK-LABEL: read_f64
+    //
+    // CHECK: mov #1, r15
+    // CHECK-NEXT: add 0(r12), r15
+    // CHECK-NEXT: and #-2, r15
+    // CHECK-NEXT: mov r15, r13
+    // CHECK-NEXT: add #8, r13
+    // CHECK-NEXT: mov r13, 0(r12)
+    // CHECK-NEXT: mov 0(r15), r12
+    // CHECK-NEXT: mov 2(r15), r13
+    // CHECK-NEXT: mov 4(r15), r14
+    // CHECK-NEXT: mov 6(r15), r15
+    // CHECK-NEXT: ret
+    ap.next_arg()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn read_i16(ap: &mut VaList<'_>) -> i16 {
+    // CHECK-LABEL: read_i16
+    //
+    // CHECK: mov #1, r13
+    // CHECK-NEXT: add 0(r12), r13
+    // CHECK-NEXT: and #-2, r13
+    // CHECK-NEXT: mov r13, r14
+    // CHECK-NEXT: incd r14
+    // CHECK-NEXT: mov r14, 0(r12)
+    // CHECK-NEXT: mov 0(r13), r12
+    // CHECK-NEXT: ret
+    ap.next_arg()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn read_i32(ap: &mut VaList<'_>) -> i32 {
+    // CHECK-LABEL: read_i32
+    //
+    // CHECK: mov #1, r13
+    // CHECK-NEXT: add 0(r12), r13
+    // CHECK-NEXT: and #-2, r13
+    // CHECK-NEXT: mov r13, r14
+    // CHECK-NEXT: add #4, r14
+    // CHECK-NEXT: mov r14, 0(r12)
+    // CHECK-NEXT: mov 0(r13), r12
+    // CHECK-NEXT: mov 2(r13), r13
+    // CHECK-NEXT: ret
+    ap.next_arg()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn read_i64(ap: &mut VaList<'_>) -> i64 {
+    // CHECK-LABEL: read_i64
+    //
+    // CHECK: mov #1, r15
+    // CHECK-NEXT: add 0(r12), r15
+    // CHECK-NEXT: and #-2, r15
+    // CHECK-NEXT: mov r15, r13
+    // CHECK-NEXT: add #8, r13
+    // CHECK-NEXT: mov r13, 0(r12)
+    // CHECK-NEXT: mov 0(r15), r12
+    // CHECK-NEXT: mov 2(r15), r13
+    // CHECK-NEXT: mov 4(r15), r14
+    // CHECK-NEXT: mov 6(r15), r15
+    // CHECK-NEXT: ret
+    ap.next_arg()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn read_ptr(ap: &mut VaList<'_>) -> *const u8 {
+    // CHECK: read_ptr = read_i16
+    ap.next_arg()
+}