Hints#
The extent to which suggestions made by using the
register
storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).The
register
specifier affects code generation only in these ways:When used as part of the register variable extension, see Variables in Specified Registers.
When
-O0
is in use, the compiler allocates distinct stack memory for all variables that do not have theregister
storage-class specifier; ifregister
is specified, the variable may have a shorter lifespan than the code would indicate and may never be placed in memory.On some rare x86 targets,
setjmp
doesn’t save the registers in all circumstances. In those cases, GCC doesn’t allocate any variables in registers unless they are markedregister
.
The extent to which suggestions made by using the inline function specifier are effective (C99 and C11 6.7.4).
GCC will not inline any functions if the
-fno-inline
option is used or if-O0
is used. Otherwise, GCC may still be unable to inline a function for many reasons; the-Winline
option may be used to determine if a function has not been inlined and why not.