Re: [patch i386]: Unbreak bootstrap for x64 SEH enabled target

[Richard Henderson <rth at redhat dot com>]

On 10/12/2011 12:07 AM, Kai Tietz wrote:
> Hello,
> 
> by recent changes gcc begun to move code into the prologue region.
> This is for x64 SEH an issue, as here the table-information for
> prologue is limited to 255 bytes size.  So we need to avoid moving
> additional code into prologue.  To achieve this we mark all standard
> and xmm registers as prologue-used at the end of prologue.   Also we
> need to emit a memory blockage.
> 
> ChangeLog
> 
> 2011-10-12  Kai Tietz  <ktietz@redhat.com>
> 
>         * config/i386/i386.c (ix86_expand_prologue): Mark
>         for TARGET_SEH all sse/integer registers as prologue-used.
> 
> Tested for x86_64-w64-mingw32.  Ok for apply?
> 
> Regards,
> Kai
> 
> Index: i386.c
> ===================================================================
> --- i386.c      (revision 179824)
> +++ i386.c      (working copy)
> @@ -10356,7 +10356,24 @@
>       Further, prevent alloca modifications to the stack pointer from being
>       combined with prologue modifications.  */
>    if (TARGET_SEH)
> -    emit_insn (gen_prologue_use (stack_pointer_rtx));
> +    {
> +      int i;
> +
> +      /* Due limited size of prologue-code size of 255 bytes,
> +         we need to prevent scheduler to sink instructions into
> +         prologue code.  Therefore we mark all standard, sse, fpu,
> +         and the pc registers as prologue-used to prevent this.
> +         Also an memory-blockage is necessary.  */
> +      emit_insn (gen_memory_blockage ());
> +
> +      for (i = 0; i <= 7; i++)
> +        {
> +         emit_insn (gen_prologue_use (gen_rtx_REG (Pmode, AX_REG + i)));
> +         emit_insn (gen_prologue_use (gen_rtx_REG (Pmode, R8_REG + i)));
> +         emit_insn (gen_prologue_use (gen_rtx_REG (TImode, XMM0_REG + i)));
> +         emit_insn (gen_prologue_use (gen_rtx_REG (TImode, XMM8_REG + i)));
> +       }
> +    }

This is overkill.  We simply need to disable shrink-wrapping for SEH.
The easiest way to do that is to add !TARGET_SEH (and a comment) to
the simple_return pattern predicate.


r~