[Harbour] gcc 4.4.0 warnings

[Szakáts Viktor]

Hi Przemek,

With GCC 4.4.0 the binaries got a bit larger when
using HB_STRICT_ALIGNMENT, but also measurably faster.

Built with 'hbmk2 speedtst.prg' (default -gc0)

HB_STRICT_ALIGNMENT: 38.25/39.11, 38.42/39.08
default            : 43.39/44.03, 43.47/44.03

Brgds,
Viktor

On 2009.05.27., at 1:13, Przemyslaw Czerpak wrote:

> On Mon, 25 May 2009, Szak�ts Viktor wrote:
>> Thanks. What should we do in default builds? Can we safely
>> pacify the warnings while keeping performance? Should we just
>> safely suppress these warnings?
>
> I'm afraid that at least in few places GCC can strip out some of our
> code or at least change the order of some instructions and wrong  
> binaries
> will be created. It has to be fixed.
> Please note that number of optimizations which use strict aliasing is
> systematically growing up so even if I pacify the warnings for GCC4.4
> it's possible that it won't help in GCC4.5 or newer.
> So the only one clean solution is using code which operates on
> bytes to create more complex numbers. It looks more complicated
> but does not have to be much slower. It's even possible that it
> will be faster then direct access with forced casting in some modern
> CPUs. Some new CPUs which seems to work with wrong alignment also
> generate exception when some complex numbers are read from memory
> address with wrong alignment but default exception handler tries
> to complete the operation using byte access. In such case explicit
> byte access should be noticeable faster.
>
> BTW have you tried to compare speedtst results for Harbour compiled
> with and without HB_STRICT_ALIGNMENT macro?
> The comparison should be done for -gc2 output. In -gc3 PCODE is
> generated only for codeblocks.
>
> best regards,
> Przemek
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