Add tests for struct padding and self-alignment.

reference/shaders-msl-no-opt/packing/member-padding.comp

@@ -0,0 +1,19 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct SSBO
+{
+    char _m0_pad[16];
+    float a;
+    char _m1_pad[20];
+    float b;
+};
+
+kernel void main0(device SSBO& _9 [[buffer(0)]])
+{
+    _9.a = 10.0;
+    _9.b = 20.0;
+}
+

reference/shaders-msl-no-opt/packing/struct-alignment.comp

@@ -0,0 +1,25 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct Foo
+{
+    packed_float3 a;
+    float b;
+};
+
+struct SSBO
+{
+    float2 a;
+    float b;
+    char _m2_pad[4];
+    Foo foo;
+};
+
+kernel void main0(device SSBO& _12 [[buffer(0)]])
+{
+    _12.a.x = 10.0;
+    _12.b = 20.0;
+}
+

shaders-msl-no-opt/packing/member-padding.comp

@@ -0,0 +1,14 @@
+#version 450
+layout(local_size_x = 1) in;
+
+layout(std140, set = 0, binding = 0) buffer SSBO
+{
+	layout(offset = 16) float a;
+	layout(offset = 40) float b;
+};
+
+void main()
+{
+	a = 10.0;
+	b = 20.0;
+}

shaders-msl-no-opt/packing/struct-alignment.comp

@@ -0,0 +1,22 @@
+#version 450
+layout(local_size_x = 1) in;
+
+struct Foo
+{
+	vec3 a; // <- This one should become packed_float3, and the MSL alignment of the struct is now 4.
+	float b;
+};
+
+layout(std140, set = 0, binding = 0) buffer SSBO
+{
+	vec2 a;
+	float b;
+	// <- We expect 4 bytes of padding here since MSL alignment of Foo must be lowered to 4.
+	Foo foo;
+};
+
+void main()
+{
+	a.x = 10.0;
+	b = 20.0;
+}