Re: (-Os versus -O2 relation) Was: case where gcc generates bigger binaries than MSVC

[Michael Meissner <meissner at cygnus dot com>]

On Thu, May 11, 2000 at 10:25:16AM +0200, Jan Hubicka wrote:
> I am not sure about DATA_ALIGNMENT. The decision IMO that needs to be made
> is whether we want -O2 and -Os code to be combined.
> At XaoS I compile main engine with -O2 and user interface with -Os.
> In case the static storage comming from -Os will be missaligned, we will
> get penalty on -O2 code.

DATA_ALIGNMENT and CONSTANT_ALIGNMENT are to add to the alignment to make
things more cache friendly, particularly in aligning the 31-byte string that is
strcpy'ed in dhrystone 2.1 so that RISC machines can do word load/stores
instead of byte load/stores.  By the way, on machines that don't have the
equivalent of REP MOVS, making DATA_ALIGNMENT and CONSTANT_ALIGNMENT smaller
will actually make the text space larger (if the alignment allows a string to
be put on a word or double word boundary, and you are moving into a suitablly
aligned structure, you need fewer loads and stores).

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Michael Meissner, Cygnus Solutions, a Red Hat company.
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