Re: [EGCS] Re: double alignment patch for x86

[Marc Lehmann <pcg@goof.com>]

>  > IMHO, the stack should always be aligned to an 8 byte boundary unless you
>  > specifically ask for it otherwise (-fspace for instance).  Otherwise, your
>  > caller may not have aligned the stack properly.
>That's one way to approach the problem, but it results in an extra insn to
>mask off the low bits of the stack in the prologue.

One thing that bugs me for months now (need advice):

gcc currently ignores the alignment set by FUNCTION_ARG_BOUNDARY
on machines that use push instructions to store arguments. This
results in incorrect code (caller forgets the necessary padding)
with the proposed -marg-align-double.

I'd like to fix this... so... where would be the place to do that?
Should store_one_arg add padding, or should this be done in expand_call?

>Options which increase the minimum alignment requirements for stack objects
>implicitly depend on the OS, crt0 and friends to maintain proper alignment.

We could make the switch dependent on the OS (Linux -> do, solaris -> ignore).
That's somewhat ugly, but it doesn't break any programs.

In worst case we could simply default this switch to off.

>[ Which is why I would generally discourage options which work in this
>  manner. ]

I'd say we shouldn't discourage options that can easily double
code speed, with only minimal changes. And on many machines,
you have more alignment than the standard says anyway.

      -----==-
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      ---==---(_)__  __ ____  __       Marc Lehmann
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    The choice of a GNU generation