[ros-dev] [ros-diffs] [akhaldi] 52114: [CMAKE] * Fix several modules to compile with the recent gcc versions. * ReactOS now compiles with mingw-w64 gcc 4.6.0 and boots to shell. * Dedicated to dreimer.

[Alex Ionescu]

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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