Re: [PATCH] [i386] Recompute the frame layout less often

[Daniel Santos <daniel dot santos at pobox dot com>]

On 05/16/2017 12:19 PM, Ian Lance Taylor wrote:
> On Mon, May 15, 2017 at 10:00 PM, Daniel Santos <daniel.santos@pobox.com> wrote:
> > Ian, would you mind looking at this please?  A combination of my
> > -mcall-ms2sysv-xlogues patch with Bernd's patch is causing problems when
> > ix86_expand_split_stack_prologue() calls ix86_expand_call().
> I don't have a lot of context here.  I assume that ms2sysv is going to
> be used on Windows systems, where -fsplit-stack isn't really going to
> work anyhow, so I think it would probably be OK that reject that
> combination if it causes trouble.

Sorry I wasn't more specific.  This -mcall-ms2sysv-xlogues actually 
targets Wine, although they don't use -fsplit-stack.  My patch set as-is 
is disabled when fsplit-stack is used, but during 
ix86_compute_frame_layout, which is too late in the case of 
-fsplit-stack.  I think I should just change this to a sorry() in 
ix86_option_override_internal.

> Also, it's overkill for ix86_expand_split_stack_prologue to call
> ix86_expand_call.  The call is always to __morestack, and __morestack
> is written in assembler, so we could use a simpler version of
> ix86_expand_call if that helps.  In particular we can decide that
> __morestack doesn't clobber any unusual registers, if that is what is
> causing the problem.
>
> Ian

Well aside from the conflict of the two patches, it just looks like it 
has the potential to generate clobbers where none are needed, but I'm 
having trouble actually *proving* that, so maybe I'm just wrong.

Daniel