Implement Linux-style likely()/unlikely() macros

This implement branch prediction macros likely() and unlikely() like in
Linux. When using these macros please ensure that when you use them the
condition in the branch really is very, very likely or unlikely. Think
90+% of the time. Primarily useful for error checking. (And I implement
these macros for all our error checking macros now)

See this article for more information:
https://kernelnewbies.org/FAQ/LikelyUnlikely

There are more places where these macros may make sense in renderer and
physics engine. Placing them will come in another commit down the line.

core/error_macros.h

@@ -30,6 +30,7 @@
 #ifndef ERROR_MACROS_H
 #define ERROR_MACROS_H
 
+#include "typedefs.h"
 /**
  * Error macros. Unlike exceptions and asserts, these macros try to mantain consistency and stability
  * inside the code. It is recommended to always return processable data, so in case of an error, the
@@ -130,7 +131,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_INDEX(m_index, m_size)                                                                                    \
 	do {                                                                                                                   \
-		if ((m_index) < 0 || (m_index) >= (m_size)) {                                                                      \
+		if (unlikely((m_index) < 0 || (m_index) >= (m_size))) {                                                            \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Index " _STR(m_index) " out of size (" _STR(m_size) ")."); \
 			return;                                                                                                        \
 		} else                                                                                                             \
@@ -144,7 +145,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_INDEX_V(m_index, m_size, m_retval)                                                                        \
 	do {                                                                                                                   \
-		if ((m_index) < 0 || (m_index) >= (m_size)) {                                                                      \
+		if (unlikely((m_index) < 0 || (m_index) >= (m_size))) {                                                            \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Index " _STR(m_index) " out of size (" _STR(m_size) ")."); \
 			return m_retval;                                                                                               \
 		} else                                                                                                             \
@@ -156,7 +157,7 @@ extern bool _err_error_exists;
 */
 #define CRASH_BAD_INDEX(m_index, m_size)                                                                                          \
 	do {                                                                                                                          \
-		if ((m_index) < 0 || (m_index) >= (m_size)) {                                                                             \
+		if (unlikely((m_index) < 0 || (m_index) >= (m_size))) {                                                                   \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "FATAL: Index " _STR(m_index) " out of size (" _STR(m_size) ")."); \
 			GENERATE_TRAP                                                                                                         \
 		}                                                                                                                         \
@@ -168,7 +169,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_NULL(m_param)                                                                              \
 	{                                                                                                       \
-		if (!m_param) {                                                                                     \
+		if (unlikely(!m_param)) {                                                                           \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Parameter ' " _STR(m_param) " ' is null."); \
 			return;                                                                                         \
 		} else                                                                                              \
@@ -177,7 +178,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_NULL_V(m_param, m_retval)                                                                  \
 	{                                                                                                       \
-		if (!m_param) {                                                                                     \
+		if (unlikely(!m_param)) {                                                                           \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Parameter ' " _STR(m_param) " ' is null."); \
 			return m_retval;                                                                                \
 		} else                                                                                              \
@@ -190,7 +191,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_COND(m_cond)                                                                              \
 	{                                                                                                      \
-		if (m_cond) {                                                                                      \
+		if (unlikely(m_cond)) {                                                                            \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Condition ' " _STR(m_cond) " ' is true."); \
 			return;                                                                                        \
 		} else                                                                                             \
@@ -202,7 +203,7 @@ extern bool _err_error_exists;
 
 #define CRASH_COND(m_cond)                                                                                        \
 	{                                                                                                             \
-		if (m_cond) {                                                                                             \
+		if (unlikely(m_cond)) {                                                                                   \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "FATAL: Condition ' " _STR(m_cond) " ' is true."); \
 			GENERATE_TRAP                                                                                         \
 		}                                                                                                         \
@@ -216,7 +217,7 @@ extern bool _err_error_exists;
 
 #define ERR_FAIL_COND_V(m_cond, m_retval)                                                                                            \
 	{                                                                                                                                \
-		if (m_cond) {                                                                                                                \
+		if (unlikely(m_cond)) {                                                                                                      \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Condition ' " _STR(m_cond) " ' is true. returned: " _STR(m_retval)); \
 			return m_retval;                                                                                                         \
 		} else                                                                                                                       \
@@ -229,7 +230,7 @@ extern bool _err_error_exists;
 
 #define ERR_CONTINUE(m_cond)                                                                                             \
 	{                                                                                                                    \
-		if (m_cond) {                                                                                                    \
+		if (unlikely(m_cond)) {                                                                                          \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Condition ' " _STR(m_cond) " ' is true. Continuing..:"); \
 			continue;                                                                                                    \
 		} else                                                                                                           \
@@ -242,7 +243,7 @@ extern bool _err_error_exists;
 
 #define ERR_BREAK(m_cond)                                                                                              \
 	{                                                                                                                  \
-		if (m_cond) {                                                                                                  \
+		if (unlikely(m_cond)) {                                                                                        \
 			_err_print_error(FUNCTION_STR, __FILE__, __LINE__, "Condition ' " _STR(m_cond) " ' is true. Breaking..:"); \
 			break;                                                                                                     \
 		} else                                                                                                         \

core/typedefs.h

@@ -290,4 +290,12 @@ struct _GlobalLock {
 #define __STRX(m_index) #m_index
 #define __STR(m_index) __STRX(m_index)
 
+#ifdef __GNUC__
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+#define likely(x) x
+#define unlikely(x) x
+#endif
+
 #endif /* typedefs.h */

core/variant.cpp

@@ -2469,10 +2469,10 @@ Variant::Variant(const Vector<Color> &p_array) {
 
 void Variant::operator=(const Variant &p_variant) {
 
-	if (this == &p_variant)
+	if (unlikely(this == &p_variant))
 		return;
 
-	if (type != p_variant.type) {
+	if (unlikely(type != p_variant.type)) {
 		reference(p_variant);
 		return;
 	}

modules/gdscript/gd_function.cpp

@@ -42,7 +42,7 @@ Variant *GDFunction::_get_variant(int p_address, GDInstance *p_instance, GDScrip
 
 		case ADDR_TYPE_SELF: {
 
-			if (!p_instance) {
+			if (unlikely(!p_instance)) {
 				r_error = "Cannot access self without instance.";
 				return NULL;
 			}
@@ -54,7 +54,7 @@ Variant *GDFunction::_get_variant(int p_address, GDInstance *p_instance, GDScrip
 		} break;
 		case ADDR_TYPE_MEMBER: {
 			//member indexing is O(1)
-			if (!p_instance) {
+			if (unlikely(!p_instance)) {
 				r_error = "Cannot access member without instance.";
 				return NULL;
 			}
@@ -279,7 +279,7 @@ Variant GDFunction::call(GDInstance *p_instance, const Variant **p_args, int p_a
 #define GET_VARIANT_PTR(m_v, m_code_ofs)                                                       \
 	Variant *m_v;                                                                              \
 	m_v = _get_variant(_code_ptr[ip + m_code_ofs], p_instance, _class, self, stack, err_text); \
-	if (!m_v)                                                                                  \
+	if (unlikely(!m_v))                                                                        \
 		break;
 
 #else