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4.8 Hints
-
The extent to which suggestions made by using the
register
storage-class specifier are effective (C90 6.5.1, C99 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 the
register
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 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.
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