Hi,
On 2011-06-06, at 4:59 PM, Dmitry Gorbachev wrote:
How does -Ofast increase size compared to -O3?
I had in mind -Ofast or -O3 versus -Os (which is used by default when building ReactOS). Now I realise you probably meant -- consider replacing -O3 by -Ofast...
Yes, I thought -O3 was the default on CMAKE builds. So I was recommending -Ofast instead of -O3, indeed.
BTW, will it be possible to compile kernel-mode code and user-mode code with different sets of options? Somebody might want to build user-mode stuff with more optimization then it's allowed for the kernel.
In fact, with GCC 4.6.0 it's even possible to do this at the function-level.
I'm not sure why you would want kernel code to be "smaller" instead of "faster" though -- on modern processors for cases like interrupts and such, large-but-correctly-aligned-and-optimized code is faster than less-bytes-per-instruction/opcode-packed code.
ie:
mov eax, [foo] add eax, 1 mov [foo], eax
is faster than
inc [foo]
-- Best regards, Alex Ionescu
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