Bug 1814600 - Annotate abort calls as __attribute__((nomerge)) to get clearer line number when crashing on assertion failure. r=gsvelto,yjuglaret

Differential Revision: https://phabricator.services.mozilla.com/D168960

mfbt/Assertions.h

@@ -210,13 +210,13 @@ MOZ_NoReturn(int aLine) {
 #    define MOZ_REALLY_CRASH(line)                                  \
       do {                                                          \
         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
-        ::abort();                                                  \
+        MOZ_NOMERGE ::abort();                                      \
       } while (false)
 #  else
 #    define MOZ_REALLY_CRASH(line)                                  \
       do {                                                          \
         *((volatile int*)MOZ_CRASH_WRITE_ADDR) = line; /* NOLINT */ \
-        abort();                                                    \
+        MOZ_NOMERGE abort();                                        \
       } while (false)
 #  endif
 #endif

mfbt/Attributes.h

@@ -88,6 +88,22 @@
 #  endif
 #endif
 
+/**
+ * Per clang's documentation:
+ *
+ * If a statement is marked nomerge and contains call expressions, those call
+ * expressions inside the statement will not be merged during optimization. This
+ * attribute can be used to prevent the optimizer from obscuring the source
+ * location of certain calls.
+ *
+ * This is useful to have clearer information on assertion failures.
+ */
+#if defined(__clang__) && __has_attribute(nomerge)
+#  define MOZ_NOMERGE __attribute__((nomerge))
+#else
+#  define MOZ_NOMERGE
+#endif
+
 /*
  * MOZ_NEVER_INLINE is a macro which expands to tell the compiler that the
  * method decorated with it must never be inlined, even if the compiler would