Preventing gcc from aligning stack???

[Johan Kullstam]

"H. Peter Anvin" <hpa en transmeta.com> writes:

> Tuukka Toivonen wrote:
> > 
> > On 25 Jan 2000, H. Peter Anvin wrote:
> > 
> > > The native fp format on IA32 is "long double" -- 80 bits (10 bytes).
> > 
> > Yes, but this is not relevant here. The 10byte floating point is used in
> > practice only internally to the FPU. Yes, you can read and store it but
> > nobody does that, since it's so much slower than a normal float or double
> > (on Pentium, atleast).
> > 
> 
> You have to if you're going to spill a register.

you'd like to think so, wouldn't you.

i recall seeing an argument about this in the gcc/egcs list (about a
year ago) wrt g77 but i think it applied to all the gcc family of
compilers.  fp register spills go into a 64 bit memory location.  yes,
this loses precision.  yes, this spill and subsequent loss of
precision is dependent upon the surrounding code, optimization level,
phase of the moon and is therefore hard to predict by the programmer.

besides, the x86 sucks at reading/storing 80 bit quantities.  they are
hard to align and not waste space &c.  welcome to the world of intel
architechure.

-- 
J o h a n  K u l l s t a m
[kullstam en ne.mediaone.net]
Don't Fear the Penguin!

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