[x86] Fix PR target/48142

[Uros Bizjak]

Hello!

> this is a regression present for x86-64 on mainline and 4.6 branch with the
> options -Os -mpreferred-stack-boundary=5 -fstack-check -fno-omit-frame-pointer.
> This improbable combination of options is necessary because you need to have
> stack checking + stack realignment + !ACCUMULATE_OUTGOING_ARGS.  In this case,
> the DW_CFA_GNU_args_size CFIs must be correct in spite of the frame pointer.
>
> Tested on {i586,x86_64}-suse-linux, OK for mainline and 4.6 branch?
>
>
> 2011-03-30  Eric Botcazou  <ebotcazou@adacore.com>
>
> 	PR target/48142
> 	* config/i386/i386.c (ix86_adjust_stack_and_probe): Differentiate
> 	frame-related from frame-unrelated adjustments to the stack pointer.

-  cfun->machine->fs.sp_offset += size;
+
+  /* Even if the stack pointer isn't the CFA register, we need to correctly
+     describe the adjustments made to it, in particular differentiate the
+     frame-related ones from the frame-unrelated ones.  */
+  if (size > 0)
+    {
+      rtx expr = gen_rtx_SEQUENCE (VOIDmode, rtvec_alloc (2));
+      XVECEXP (expr, 0, 0)
+	= gen_rtx_SET (VOIDmode, stack_pointer_rtx,
+		       plus_constant (stack_pointer_rtx, -size));
+      XVECEXP (expr, 0, 1)
+	= gen_rtx_SET (VOIDmode, stack_pointer_rtx,
+		       plus_constant (stack_pointer_rtx,
+				      PROBE_INTERVAL + dope + size));
+      add_reg_note (last, REG_FRAME_RELATED_EXPR, expr);
+      RTX_FRAME_RELATED_P (last) = 1;
+
+      cfun->machine->fs.sp_offset += size;
+    }

Is there a reason why we can't just cancel (+ size and -size) in these
two expressions to:

 XVECEXP (expr, 0, 0)
	= gen_rtx_SET (VOIDmode, stack_pointer_rtx,
		       plus_constant (stack_pointer_rtx,
				      PROBE_INTERVAL + dope));

Uros.