1 files changed, 103 insertions, 0 deletions
diff --git a/compiler/rustc_target/src/callconv/wasm.rs b/compiler/rustc_target/src/callconv/wasm.rs
new file mode 100644
index 00000000000..3c4cd76a754
--- /dev/null
+++ b/compiler/rustc_target/src/callconv/wasm.rs
@@ -0,0 +1,103 @@
+use crate::abi::call::{ArgAbi, FnAbi};
+use crate::abi::{HasDataLayout, TyAbiInterface};
+
+fn unwrap_trivial_aggregate<'a, Ty, C>(cx: &C, val: &mut ArgAbi<'a, Ty>) -> bool
+where
+    Ty: TyAbiInterface<'a, C> + Copy,
+    C: HasDataLayout,
+{
+    if val.layout.is_aggregate() {
+        if let Some(unit) = val.layout.homogeneous_aggregate(cx).ok().and_then(|ha| ha.unit()) {
+            let size = val.layout.size;
+            if unit.size == size {
+                val.cast_to(unit);
+                return true;
+            }
+        }
+    }
+    false
+}
+
+fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>)
+where
+    Ty: TyAbiInterface<'a, C> + Copy,
+    C: HasDataLayout,
+{
+    ret.extend_integer_width_to(32);
+    if ret.layout.is_aggregate() && !unwrap_trivial_aggregate(cx, ret) {
+        ret.make_indirect();
+    }
+}
+
+fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>)
+where
+    Ty: TyAbiInterface<'a, C> + Copy,
+    C: HasDataLayout,
+{
+    if !arg.layout.is_sized() {
+        // Not touching this...
+        return;
+    }
+    arg.extend_integer_width_to(32);
+    if arg.layout.is_aggregate() && !unwrap_trivial_aggregate(cx, arg) {
+        arg.make_indirect();
+    }
+}
+
+/// The purpose of this ABI is to match the C ABI (aka clang) exactly.
+pub(crate) fn compute_c_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
+where
+    Ty: TyAbiInterface<'a, C> + Copy,
+    C: HasDataLayout,
+{
+    if !fn_abi.ret.is_ignore() {
+        classify_ret(cx, &mut fn_abi.ret);
+    }
+
+    for arg in fn_abi.args.iter_mut() {
+        if arg.is_ignore() {
+            continue;
+        }
+        classify_arg(cx, arg);
+    }
+}
+
+/// The purpose of this ABI is for matching the WebAssembly standard. This
+/// intentionally diverges from the C ABI and is specifically crafted to take
+/// advantage of LLVM's support of multiple returns in WebAssembly.
+///
+/// This ABI is *bad*! It uses `PassMode::Direct` for `abi::Aggregate` types, which leaks LLVM
+/// implementation details into the ABI. It's just hard to fix because ABIs are hard to change.
+/// Also see <https://github.com/rust-lang/rust/issues/115666>.
+pub(crate) fn compute_wasm_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
+    if !fn_abi.ret.is_ignore() {
+        classify_ret_wasm_abi(&mut fn_abi.ret);
+    }
+
+    for arg in fn_abi.args.iter_mut() {
+        if arg.is_ignore() {
+            continue;
+        }
+        classify_arg_wasm_abi(arg);
+    }
+
+    fn classify_ret_wasm_abi<Ty>(ret: &mut ArgAbi<'_, Ty>) {
+        if !ret.layout.is_sized() {
+            // Not touching this...
+            return;
+        }
+        // FIXME: this is bad! https://github.com/rust-lang/rust/issues/115666
+        ret.make_direct_deprecated();
+        ret.extend_integer_width_to(32);
+    }
+
+    fn classify_arg_wasm_abi<Ty>(arg: &mut ArgAbi<'_, Ty>) {
+        if !arg.layout.is_sized() {
+            // Not touching this...
+            return;
+        }
+        // FIXME: this is bad! https://github.com/rust-lang/rust/issues/115666
+        arg.make_direct_deprecated();
+        arg.extend_integer_width_to(32);
+    }
+}