add Int support to amd64 and fix issue with structs not being copied

struct_amd64.go

@@ -111,7 +111,7 @@ func addStruct(v reflect.Value, numInts, numFloats, numStack *int, addInt, addFl
 	return keepAlive
 }
 
-func postMerger(t reflect.Type) bool {
+func postMerger(t reflect.Type) (passInMemory bool) {
 	// (c) If the size of the aggregate exceeds two eightbytes and the first eight- byte isn’t SSE or any other
 	// eightbyte isn’t SSEUP, the whole argument is passed in memory.
 	if t.Kind() != reflect.Struct {
@@ -120,19 +120,7 @@ func postMerger(t reflect.Type) bool {
 	if t.Size() <= 2*8 {
 		return false
 	}
-	first := getFirst(t).Kind()
-	if first != reflect.Float32 && first != reflect.Float64 {
-		return false
-	}
-	return true
-}
-
-func getFirst(t reflect.Type) reflect.Type {
-	first := t.Field(0).Type
-	if first.Kind() == reflect.Struct {
-		return getFirst(first)
-	}
-	return first
+	return true // Go does not have an SSE/SEEUP type so this is always true
 }
 
 func tryPlaceRegister(v reflect.Value, addFloat func(uintptr), addInt func(uintptr)) (ok bool) {
@@ -196,7 +184,7 @@ func tryPlaceRegister(v reflect.Value, addFloat func(uintptr), addInt func(uintp
 				val |= uint64(f.Int()&0xFFFF_FFFF) << shift
 				shift += 32
 				class |= _INTEGER
-			case reflect.Int64:
+			case reflect.Int64, reflect.Int:
 				val = uint64(f.Int())
 				shift = 64
 				class = _INTEGER
@@ -212,7 +200,7 @@ func tryPlaceRegister(v reflect.Value, addFloat func(uintptr), addInt func(uintp
 				val |= f.Uint() << shift
 				shift += 32
 				class |= _INTEGER
-			case reflect.Uint64:
+			case reflect.Uint64, reflect.Uint:
 				val = f.Uint()
 				shift = 64
 				class = _INTEGER

struct_test.go

@@ -6,6 +6,7 @@
 package purego_test
 
 import (
+	"math"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -440,6 +441,28 @@ func TestRegisterFunc_structArgs(t *testing.T) {
 			t.Fatalf("InitWithContentRect returned %d wanted %#x", ret, expectedUnsigned)
 		}
 	}
+	{
+		type GoInt4 struct {
+			A, B, C, D int
+		}
+		var GoInt4Fn func(GoInt4) int
+		purego.RegisterLibFunc(&GoInt4Fn, lib, "GoInt4")
+		const expected = math.MaxInt - 52 - 3 + 4
+		if ret := GoInt4Fn(GoInt4{math.MaxInt, -52, 3, 4}); ret != expected {
+			t.Fatalf("GoInt4Fn returned %d wanted %#x", ret, expected)
+		}
+	}
+	{
+		type GoUint4 struct {
+			A, B, C, D uint
+		}
+		var GoUint4Fn func(GoUint4) uint
+		purego.RegisterLibFunc(&GoUint4Fn, lib, "GoUint4")
+		const expected = 1_000_000 + 53 + 71 + 8
+		if ret := GoUint4Fn(GoUint4{1_000_000, 53, 71, 8}); ret != expected {
+			t.Fatalf("GoUint4Fn returned %d wanted %#x", ret, expected)
+		}
+	}
 }
 
 func TestRegisterFunc_structReturns(t *testing.T) {

testdata/structtest/struct_test.c

@@ -1,6 +1,13 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: 2024 The Ebitengine Authors
 
+#include "stdint.h"
+
+#if defined(__x86_64__) || defined(__aarch64__)
+typedef int64_t GoInt;
+typedef uint64_t GoUint;
+#endif
+
 // Empty is empty
 struct Empty {};
 
@@ -325,3 +332,19 @@ unsigned long InitWithContentRect(int *win, struct Content c, int style, int bac
       return 0xF1A6; // FLAG
   return (unsigned long)(c.point.x + c.point.y + c.size.width + c.size.height) / (style - backing);
 }
+
+struct GoInt4 {
+    GoInt a, b, c, d;
+};
+
+GoInt GoInt4(struct GoInt4 g) {
+    return g.a + g.b - g.c + g.d;
+}
+
+struct GoUint4 {
+    GoUint a, b, c, d;
+};
+
+GoUint GoUint4(struct GoUint4 g) {
+    return g.a + g.b + g.c + g.d;
+}