Re: [MinGW-dvlpr] Re: _alloca/_chkstk??

[Danny S. <dan...@cl...>]

----- Original Message ----- 
From: "Ranjit Mathew
> Luke Dunstan wrote:
> >>>>Is there a particular reason to remove it
> >>>>though, apart from when statically linking
> >>>>GCC-compiled objects with MSVC programs
> >>>>or vice versa?
> >>>
> >>>Yes, it plays up with optimisation using
> >>>-funit-at-a-time in CVS gcc,
> >>
> >>More specifically, -funit-at-a-time (which is
> >>now enabled by -O2) changes the calling
> >>conventions of local functions (functions that
> >>are defined, accessible and used within a single
> >>compilation unit) to use as many (max. three?)
> >>registers for passing parameters as possible.
> >>
> >>MinGW/Cygwin's current implementation of
> >>__chkstk/_alloca clobbers EAX, resulting in
> >>a parameter to local functions getting
> >>converted to garbage.
> > 
> > 
> > Then perhaps "-funit-at-a-time" on MinGW should imply
> > "-mno-stack-arg-probe".
> 
> A simpler solution would be to limit
> the registers used by -funit-at-a-time
> to the stock ECX & EDX.
> 
> It appears that this is a simple matter
> of changing contents of the very last "if"
> condition in ix86_function_regparm( )
> in gcc/config/i386/i386.c (let regparm
> be equal to 2 always). Of course,
> I could be mistaken and this might not
> be so simple to fix after all.
> 

Their is an ABI issue here.  Wouldn't that seriously break library code
using the old meaning of  regparm?
Changing cygwin.asm is also questionable.

Ranjit, have you discussed your ix86_function_regparm approach
 with Honza, who is assigned the bug (PR12209) 
 
Danny.
> 
> -- 
> Ranjit Mathew          Email: rmathew AT hotmail DOT com
> 
> Bangalore, INDIA.      Web: http://ranjitmathew.tripod.com/
> 
> 
> 
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