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Add likely() and unlikely() for our assertions

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Allows the compiler to know our bespoke assert functions
are cold paths. This would normally occur somehow for real assert().
Assembly does appear it will save some branches.

Also don't worry about NDEBUG

(This doesn't matter because we rolled our own assert functions.
Thanks @zanchey.)
This commit is contained in:
Aaron Gyes 2021-09-28 23:31:47 -07:00
parent a5978eade4
commit 97bb53e32d
3 changed files with 15 additions and 9 deletions
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3
CMakeLists.txt
View file

@ -19,9 +19,6 @@ set(DEFAULT_BUILD_TYPE "RelWithDebInfo")
# Generate Xcode schemas (but not for tests).
set(CMAKE_XCODE_GENERATE_SCHEME 1)
# Use the default flags (#6296) but undefine NDEBUG so that asserts remain enabled.
add_definitions(-UNDEBUG)
if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
message(STATUS "Setting build type to default '${DEFAULT_BUILD_TYPE}'")
set(CMAKE_BUILD_TYPE "${DEFAULT_BUILD_TYPE}")

10
src/common.cpp
View file

@ -1780,7 +1780,7 @@ void restore_term_foreground_process_group_for_exit() {
bool is_main_thread() { return thread_id() == 1; }
void assert_is_main_thread(const char *who) {
if (!is_main_thread() && !thread_asserts_cfg_for_testing) {
if (!likely(is_main_thread()) && !unlikely(thread_asserts_cfg_for_testing)) {
FLOGF(error, L"%s called off of main thread.", who);
FLOGF(error, L"Break on debug_thread_error to debug.");
debug_thread_error();
@ -1788,7 +1788,7 @@ void assert_is_main_thread(const char *who) {
}
void assert_is_not_forked_child(const char *who) {
if (is_forked_child()) {
if (unlikely(is_forked_child())) {
FLOGF(error, L"%s called in a forked child.", who);
FLOG(error, L"Break on debug_thread_error to debug.");
debug_thread_error();
@ -1796,7 +1796,7 @@ void assert_is_not_forked_child(const char *who) {
}
void assert_is_background_thread(const char *who) {
if (is_main_thread() && !thread_asserts_cfg_for_testing) {
if (unlikely(is_main_thread()) && !unlikely(thread_asserts_cfg_for_testing)) {
FLOGF(error, L"%s called on the main thread (may block!).", who);
FLOG(error, L"Break on debug_thread_error to debug.");
debug_thread_error();
@ -1806,7 +1806,7 @@ void assert_is_background_thread(const char *who) {
void assert_is_locked(std::mutex &mutex, const char *who, const char *caller) {
// Note that std::mutex.try_lock() is allowed to return false when the mutex isn't
// actually locked; fortunately we are checking the opposite so we're safe.
if (mutex.try_lock()) {
if (unlikely(mutex.try_lock())) {
FLOGF(error, L"%s is not locked when it should be in '%s'", who, caller);
FLOG(error, L"Break on debug_thread_error to debug.");
debug_thread_error();
@ -1843,7 +1843,7 @@ void redirect_tty_output() {
/// Display a failed assertion message, dump a stack trace if possible, then die.
[[noreturn]] void __fish_assert(const char *msg, const char *file, size_t line, int error) {
if (error) {
if (unlikely(error)) {
FLOGF(error, L"%s:%zu: failed assertion: %s: errno %d (%s)", file, line, msg, error,
std::strerror(error));
} else {

11
src/common.h
View file

@ -222,7 +222,7 @@ extern const wcstring g_empty_string;
#define DIE_ON_FAILURE(e) \
do { \
int status = e; \
if (status != 0) { \
if (unlikely(status != 0)) { \
__fish_assert(#e, __FILE__, __LINE__, status); \
} \
} while (0)
@ -308,6 +308,15 @@ void wcs2string_appending(const wchar_t *in, size_t len, std::string *receiver);
#define TESTS_PROGRAM_NAME L"(ignore)"
bool should_suppress_stderr_for_tests();
/// Branch prediction hints. Idea borrowed from Linux kernel. Just used for asserts.
#if __has_builtin(__builtin_expect)
#define likely(x) __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#else
#define likely(x) (x)
#define unlikely(x) (x)
#endif
void assert_is_main_thread(const char *who);
#define ASSERT_IS_MAIN_THREAD_TRAMPOLINE(x) assert_is_main_thread(x)
#define ASSERT_IS_MAIN_THREAD() ASSERT_IS_MAIN_THREAD_TRAMPOLINE(__FUNCTION__)