util: Replace the usage of ALIGN16 with alignas(16) and them remove ALIGN16 macro

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19565>

src/freedreno/vulkan/tu_device.h

@@ -184,7 +184,7 @@ struct tu6_global
       uint32_t pad[7];
    } flush_base[4];
 
-   ALIGN16 uint32_t cs_indirect_xyz[3];
+   alignas(16) uint32_t cs_indirect_xyz[3];
 
    volatile uint32_t vtx_stats_query_not_running;
 

src/gallium/auxiliary/tgsi/tgsi_exec.c

@@ -73,18 +73,27 @@
 #define TILE_BOTTOM_LEFT  2
 #define TILE_BOTTOM_RIGHT 3
 
+static_assert(alignof(union tgsi_exec_channel) == 16, "");
+static_assert(alignof(struct tgsi_exec_vector) == 16, "");
+static_assert(alignof(struct tgsi_exec_machine) == 16, "");
+
 union tgsi_double_channel {
+   alignas(16)
    double d[TGSI_QUAD_SIZE];
    unsigned u[TGSI_QUAD_SIZE][2];
    uint64_t u64[TGSI_QUAD_SIZE];
    int64_t i64[TGSI_QUAD_SIZE];
-} ALIGN16;
+};
 
-struct ALIGN16 tgsi_double_vector {
+struct tgsi_double_vector {
+   alignas(16)
    union tgsi_double_channel xy;
    union tgsi_double_channel zw;
 };
 
+static_assert(alignof(union tgsi_double_channel) == 16, "");
+static_assert(alignof(struct tgsi_double_vector) == 16, "");
+
 static void
 micro_abs(union tgsi_exec_channel *dst,
           const union tgsi_exec_channel *src)

src/gallium/auxiliary/tgsi/tgsi_exec.h

@@ -73,17 +73,18 @@ extern "C" {
   */
 union tgsi_exec_channel
 {
+   alignas(16)
    float    f[TGSI_QUAD_SIZE];
    int      i[TGSI_QUAD_SIZE];
    unsigned u[TGSI_QUAD_SIZE];
-} ALIGN16;
+};
 
 /**
   * A vector[RGBA] of channels[4 pixels]
   */
-struct ALIGN16 tgsi_exec_vector
+struct tgsi_exec_vector
 {
-   union tgsi_exec_channel xyzw[TGSI_NUM_CHANNELS];
+   alignas(16) union tgsi_exec_channel xyzw[TGSI_NUM_CHANNELS];
 };
 
 /**
@@ -286,10 +287,11 @@ typedef void (* apply_sample_offset_func)(
 /**
  * Run-time virtual machine state for executing TGSI shader.
  */
-struct ALIGN16 tgsi_exec_machine
+struct tgsi_exec_machine
 {
    /* Total = program temporaries + internal temporaries
     */
+   alignas(16)
    struct tgsi_exec_vector       Temps[TGSI_EXEC_NUM_TEMPS];
 
    unsigned                       ImmsReserved;

src/mesa/math/m_matrix.h

@@ -79,8 +79,8 @@ enum GLmatrixtype {
  * Matrix type to represent 4x4 transformation matrices.
  */
 typedef struct {
-   ALIGN16 GLfloat m[16];	/**< 16 matrix elements (16-byte aligned) */
-   ALIGN16 GLfloat inv[16];	/**< 16-element inverse (16-byte aligned) */
+   alignas(16) GLfloat m[16];	/**< 16 matrix elements (16-byte aligned) */
+   alignas(16) GLfloat inv[16];	/**< 16-element inverse (16-byte aligned) */
    GLuint flags;        /**< possible values determined by (of \link
                          * MatFlags MAT_FLAG_* flags\endlink)
                          */

src/util/macros.h

@@ -215,12 +215,6 @@ do {                       \
 #  endif
 #endif
 
-#ifdef _MSC_VER
-#define ALIGN16 __declspec(align(16))
-#else
-#define ALIGN16 __attribute__((aligned(16)))
-#endif
-
 #ifdef __cplusplus
 /**
  * Macro function that evaluates to true if T is a trivially
@@ -413,6 +407,24 @@ u_uintN_max(unsigned bit_size)
    return UINT64_MAX >> (64 - bit_size);
 }
 
+/* alignas usage
+ * For struct or union, use alignas(align_size) on any member
+ * of it will make it aligned to align_size.
+ * See https://en.cppreference.com/w/c/language/_Alignas for
+ * details. We can use static_assert and alignof to check if
+ * the alignment result of alignas(align_size) on struct or 
+ * union is valid.
+ * For example:
+ *   static_assert(alignof(struct tgsi_exec_machine) == 16, "")
+ * Also, we can use special code to see the size of the aligned
+ * struct or union at the compile time with GCC, Clang or MSVC.
+ * So we can see if the size of union or struct are as expected
+ * when using alignas(align_size) on its member.
+ * For example:
+ *   char (*__kaboom)[sizeof(struct tgsi_exec_machine)] = 1;
+ * can show us the size of struct tgsi_exec_machine at compile
+ * time.
+ */
 #ifndef __cplusplus
 #ifdef _MSC_VER
 #define alignof _Alignof