Am 13.06.2010, 00:52 Uhr, schrieb Bernd Walter:
In more general terms, the compiler is allowed to make any changes it
likes to the program as long as the end result behaves exactly like it
would if it hadn't been changed. This is called the "as if" rule. For
instance, if you call printf() or fprintf() with a format string that
does not contain any conversion specifiers, gcc will call gets() or
fgets() instead.
Amazing - this is one of the things which can get nasty if you try some
kind of microtuning.
Recently I had to implement my own atoi on a controller because using the
library one magically had blown my RAM usage by 1k on a controller with
just 8k RAM.
There are certain compiler flags to affect that. For GCC, -Os is one
(which doesn't necessarily work in FreeBSD though, on some versions the
compiler would go into unterminated loop, leak memory and ultimately fail
with OOM), flags to tell the compiler that the implementation is
freestanding, and attributes to select builtins and the likes.
--
Matthias Andree
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