Sema+llvm: properly implement Interrupt callconv

Co-authored-by: Veikka Tuominen <git@vexu.eu>

src/Sema.zig

@@ -9700,6 +9700,18 @@ fn funcCommon(
         {
             return sema.fail(block, param_src, "non-pointer parameter declared noalias", .{});
         }
+
+        if (cc_resolved == .Interrupt) switch (target.cpu.arch) {
+            .x86, .x86_64 => {
+                const err_code_size = target.ptrBitWidth();
+                switch (i) {
+                    0 => if (param_ty.zigTypeTag(mod) != .Pointer) return sema.fail(block, param_src, "parameter must be a pointer type", .{}),
+                    1 => if (param_ty.bitSize(mod) != err_code_size) return sema.fail(block, param_src, "parameter must be a {d}-bit integer", .{err_code_size}),
+                    else => return sema.fail(block, param_src, "Interrupt calling convention supports up to 2 parameters, found {d}", .{i + 1}),
+                }
+            },
+            else => return sema.fail(block, param_src, "parameters are not allowed with Interrupt calling convention", .{}),
+        };
     }
 
     var ret_ty_requires_comptime = false;
@@ -10048,6 +10060,15 @@ fn finishFunc(
         });
     }
 
+    if (cc_resolved == .Interrupt and return_type.zigTypeTag(mod) != .Void) {
+        return sema.fail(
+            block,
+            cc_src,
+            "non-void return type '{}' not allowed in function with calling convention 'Interrupt'",
+            .{return_type.fmt(mod)},
+        );
+    }
+
     if (cc_resolved == .Inline and is_noinline) {
         return sema.fail(block, cc_src, "'noinline' function cannot have callconv 'Inline'", .{});
     }

src/codegen/llvm.zig

@@ -4434,6 +4434,10 @@ pub const Object = struct {
             if (!param_ty.isPtrLikeOptional(mod) and !ptr_info.flags.is_allowzero) {
                 try attributes.addParamAttr(llvm_arg_i, .nonnull, &o.builder);
             }
+            if (fn_info.cc == .Interrupt) {
+                const child_type = try lowerType(o, Type.fromInterned(ptr_info.child));
+                try attributes.addParamAttr(llvm_arg_i, .{ .byval = child_type }, &o.builder);
+            }
             if (ptr_info.flags.is_const) {
                 try attributes.addParamAttr(llvm_arg_i, .readonly, &o.builder);
             }