lib: Introduce BUILD_BUG_ON_INVALID and igt_assume()

BUILD_BUG_ON_INVALID() is a macro that, like the kernel counterpart,
expands to an expression that generates no code. Useful for making
sure an expression is valid code while producing no side effects.

igt_assume() is an assert-like macro that is used to give hints to
static analysis of code. If static analysis is not used (as detected
by STATIC_ANALYSIS_BUILD), igt_assume() expands to a
BUILD_BUG_ON_INVALID, otherwise expands to an assert().

v2: Make sure the expression in igt_assume is still parsed without
    static analysis. (Chris)

v3: Also introduce BUILD_BUG_ON_INVALID as standalone

Signed-off-by: Petri Latvala <petri.latvala@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/igt_core.h b/lib/igt_core.h
index 6f8c3852..0d02c90b 100644
--- a/lib/igt_core.h
+++ b/lib/igt_core.h
@@ -30,6 +30,7 @@
 #ifndef IGT_CORE_H
 #define IGT_CORE_H
 
+#include <assert.h>
 #include <setjmp.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -54,6 +55,30 @@
 #endif
 #endif
 
+/**
+ * BUILD_BUG_ON_INVALID:
+ * @expr: Expression
+ *
+ * A macro that takes an expression and generates no code. Used for
+ * checking at build-time that an expression is valid code.
+ */
+#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((long)(e))))
+
+/**
+ * igt_assume:
+ * @expr: Condition to test
+ *
+ * An assert-like macro to be used for tautologies to give hints to
+ * static analysis of code. No-op if STATIC_ANALYSIS_BUILD is not
+ * defined, expands to an assert() if it is.
+ */
+#if STATIC_ANALYSIS_BUILD
+#define igt_assume(e) assert(e)
+#else
+/* Make sure the expression is still parsed even though it generates no code */
+#define igt_assume(e) BUILD_BUG_ON_INVALID(e)
+#endif
+
 extern const char* __igt_test_description __attribute__((weak));
 extern bool __igt_plain_output;
 extern char *igt_frame_dump_path;