Re: Allow preferred-stack-boundary of 3 for x86-64

[Jan Hubicka <jh@suse.cz>]

> 
> I tested the patch now and I get a ICE while compiling the x86_64 linux kernel 
> with -mpreferred-stack-boundary=3  and 070727 SVN checkout + patch
> 
> /home/lsrc/quilt/linux/init/do_mounts.c: In function 'change_floppy':
> /home/lsrc/quilt/linux/init/do_mounts.c:390: internal compiler error: in ix86_compute_frame_layout, at config/i386/i386.c:5745
Hi,
this patch should fix it, I will commit it after testing on
x86_64-linux.

Honza

	* i386.c (setup_incoming_varargs_64): Tolerate 64bit preferred
	stack boundary.
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c	(revision 127065)
+++ config/i386/i386.c	(working copy)
@@ -4656,7 +4656,14 @@ setup_incoming_varargs_64 (CUMULATIVE_AR
 
   /* Indicate to allocate space on the stack for varargs save area.  */
   ix86_save_varrargs_registers = 1;
-  cfun->stack_alignment_needed = 128;
+  /* We need 16-byte stack alignment to save SSE registers.  If user
+     asked for lower preferred_stack_boundary, lets just hope that he knows
+     what he is doing and won't varargs SSE values.  
+
+     We also may end up assuming that only 64bit values are stored in SSE
+     register let some floating point program work.  */
+  if (ix86_preferred_stack_boundary >= 128)
+    cfun->stack_alignment_needed = 128;
 
   save_area = frame_pointer_rtx;
   set = get_varargs_alias_set ();