Auto merge of #88321 - glaubitz:m68k-linux, r=wesleywiser

Add initial support for m68k

This patch series adds initial support for m68k making use of the new M68k
backend introduced with LLVM-13. Additional changes will be needed to be
able to actually use the backend for this target.

compiler/rustc_target/src/abi/call/m68k.rs

@@ -0,0 +1,30 @@
+use crate::abi::call::{ArgAbi, FnAbi};
+
+fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
+    if ret.layout.is_aggregate() {
+        ret.make_indirect();
+    } else {
+        ret.extend_integer_width_to(32);
+    }
+}
+
+fn classify_arg<Ty>(arg: &mut ArgAbi<'_, Ty>) {
+    if arg.layout.is_aggregate() {
+        arg.make_indirect_byval();
+    } else {
+        arg.extend_integer_width_to(32);
+    }
+}
+
+pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
+    if !fn_abi.ret.is_ignore() {
+        classify_ret(&mut fn_abi.ret);
+    }
+
+    for arg in &mut fn_abi.args {
+        if arg.is_ignore() {
+            continue;
+        }
+        classify_arg(arg);
+    }
+}

compiler/rustc_target/src/abi/call/mod.rs

@@ -9,6 +9,7 @@ mod arm;
 mod avr;
 mod bpf;
 mod hexagon;
+mod m68k;
 mod mips;
 mod mips64;
 mod msp430;
@@ -656,6 +657,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "amdgpu" => amdgpu::compute_abi_info(cx, self),
             "arm" => arm::compute_abi_info(cx, self),
             "avr" => avr::compute_abi_info(self),
+            "m68k" => m68k::compute_abi_info(self),
             "mips" => mips::compute_abi_info(cx, self),
             "mips64" => mips64::compute_abi_info(cx, self),
             "powerpc" => powerpc::compute_abi_info(self),

compiler/rustc_target/src/spec/m68k_unknown_linux_gnu.rs

@@ -0,0 +1,15 @@
+use crate::abi::Endian;
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    let mut base = super::linux_base::opts();
+    base.max_atomic_width = Some(32);
+
+    Target {
+        llvm_target: "m68k-unknown-linux-gnu".to_string(),
+        pointer_width: 32,
+        data_layout: "E-m:e-p:32:16:32-i8:8:8-i16:16:16-i32:16:32-n8:16:32-a:0:16-S16".to_string(),
+        arch: "m68k".to_string(),
+        options: TargetOptions { endian: Endian::Big, mcount: "_mcount".to_string(), ..base },
+    }
+}

compiler/rustc_target/src/spec/mod.rs

@@ -742,6 +742,7 @@ supported_targets! {
     ("x86_64-unknown-linux-gnux32", x86_64_unknown_linux_gnux32),
     ("i686-unknown-linux-gnu", i686_unknown_linux_gnu),
     ("i586-unknown-linux-gnu", i586_unknown_linux_gnu),
+    ("m68k-unknown-linux-gnu", m68k_unknown_linux_gnu),
     ("mips-unknown-linux-gnu", mips_unknown_linux_gnu),
     ("mips64-unknown-linux-gnuabi64", mips64_unknown_linux_gnuabi64),
     ("mips64el-unknown-linux-gnuabi64", mips64el_unknown_linux_gnuabi64),