Merge #19156 #19174

19156: core/compiler_hints: add likely() / unlikely() hints r=kfessel a=benpicco



19174: tests/periph_spi clearly say when init succeeds r=benpicco a=jdavid

When the `tests/periph_spi` program succeeds the output can be interpreted as an error happened.
This PR makes it clearer when it does succeed.

### Contribution description

In `tests/periph_spi`:

- Explicitely say that the init operation was successful
- Rephrase the note to avoid misinterpretations 


### Testing procedure

Run the `tests/periph_spi` program.
There is not much to test, just to verify the output, should be like this:

```
2023-01-19 10:42:33,768 # Trying to initialize SPI_DEV(1): mode: 0, clk: 0, cs_port: 0, cs_pin: 0
2023-01-19 10:42:33,777 # (if below the program crashes with a failed assertion, then it means the configuration is not supported)
2023-01-19 10:42:33,779 # Success.
```


### Issues/PRs references

Issue https://github.com/RIOT-OS/RIOT/issues/19025

Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: J. David Ibáñez <jdavid.ibp@gmail.com>

core/lib/include/assert.h

@@ -22,6 +22,8 @@
 #ifndef ASSERT_H
 #define ASSERT_H
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -42,6 +44,9 @@ extern "C" {
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  */
 #define DEBUG_ASSERT_VERBOSE
+#else
+/* we should not include custom headers in standard headers */
+#define _likely(x)      __builtin_expect((uintptr_t)(x), 1)
 #endif
 
 /**
@@ -109,10 +114,10 @@ __NORETURN void _assert_failure(const char *file, unsigned line);
  *
  * @see http://pubs.opengroup.org/onlinepubs/9699919799/functions/assert.html
  */
-#define assert(cond) ((cond) ? (void)0 :  _assert_failure(__FILE__, __LINE__))
+#define assert(cond) (_likely(cond) ? (void)0 :  _assert_failure(__FILE__, __LINE__))
 #else /* DEBUG_ASSERT_VERBOSE */
 __NORETURN void _assert_panic(void);
-#define assert(cond) ((cond) ? (void)0 : _assert_panic())
+#define assert(cond) (_likely(cond) ? (void)0 : _assert_panic())
 #endif /* DEBUG_ASSERT_VERBOSE */
 
 #if !defined __cplusplus

core/lib/include/compiler_hints.h

@@ -21,6 +21,8 @@
 #ifndef COMPILER_HINTS_H
 #define COMPILER_HINTS_H
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -130,6 +132,24 @@ extern "C" {
 #define IS_CT_CONSTANT(expr) 0
 #endif
 
+/**
+ * @brief   Hint to the compiler that the condition @p x is likely taken
+ *
+ * @param[in] x     Condition that is likely taken
+ *
+ * @return result of @p x
+ */
+#define likely(x)       __builtin_expect((uintptr_t)(x), 1)
+
+/**
+ * @brief   Hint to the compiler that the condition @p x is likely not taken
+ *
+ * @param[in] x     Condition that is unlikely
+ *
+ * @return result of @p x
+ */
+#define unlikely(x)     __builtin_expect((uintptr_t)(x), 0)
+
 #ifdef __cplusplus
 }
 #endif

sys/include/test_utils/expect.h

@@ -26,6 +26,7 @@
 #define TEST_UTILS_EXPECT_H
 
 #include <stdio.h>
+#include "compiler_hints.h"
 #include "panic.h"
 
 #ifdef __cplusplus
@@ -76,7 +77,7 @@ NORETURN static inline void _expect_failure(const char *file, unsigned line)
  * the condition failed in.
  *
  */
-#define expect(cond) ((cond) ? (void)0 :  _expect_failure(__FILE__, __LINE__))
+#define expect(cond) (likely(cond) ? (void)0 :  _expect_failure(__FILE__, __LINE__))
 
 #ifdef __cplusplus
 }

tests/periph_spi/main.c

@@ -217,9 +217,11 @@ int cmd_init(int argc, char **argv)
     else {
         printf("Trying to initialize SPI_DEV(%i): mode: %i, clk: %i, cs_port: %i, cs_pin: %i\n",
                dev, mode, clk, port, pin);
-        puts("Note: Failed assertion (crash) means configuration not supported");
+        puts("(if below the program crashes with a failed assertion, then it means the"
+             " configuration is not supported)");
         spi_acquire(spiconf.dev, spiconf.cs, spiconf.mode, spiconf.clk);
         spi_release(spiconf.dev);
+        puts("Success.");
     }
 
     return 0;