Re: Frame-related delay slot insns

[Richard Sandiford <rsandifo at redhat dot com>]

"John David Anglin" <dave@hiauly1.hia.nrc.ca> writes:
> With respect to dwarf2 debug and exception support, we don't allow
> frame related instructions in the delay slot of branches on hppa-linux.
> This is the only PA port that supports dwarf2 exceptions.  We emit
> a blockage at the end of the prologue when doing frame notes.  This
> isn't optimal but it's the only solution so far.

I wondered about doing the same for mips, or at least changing
the delay attributes such that frame-related insns never went
into a call's delay slot.  I guess it's still plan B if the
patches to final aren't accepted.

FWIW, the in-sequence alternative might look something like
the patch below (untested).

Richard


	* dwarf2out.c (dwarf2out_frame_debug): Do nothing within delayed
	branch sequences.
	* final.c (final_scan_insn): Pass delayed branch sequences through
	dwarf2out_frame_debug before emitting them.

Index: final.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/final.c,v
retrieving revision 1.275
diff -c -d -p -F^[(a-zA-Z0-9_^#] -r1.275 final.c
*** final.c	25 Jan 2003 23:32:20 -0000	1.275
--- final.c	6 May 2003 16:57:04 -0000
*************** #endif
*** 2158,2163 ****
--- 2158,2173 ----
  
  	    if (prescan > 0)
  	      break;
+ 
+ 	    /* When a call's delay slots include frame-related insns,
+ 	       their effect must be described before the call.  See
+ 	       execute_cfa_program().  */
+ #if defined (DWARF2_UNWIND_INFO)
+ 	    if (dwarf2out_do_frame ())
+ 	      for (i = 0; i < XVECLEN (body, 0); i++)
+ 		dwarf2out_frame_debug (XVECEXP (body, 0, i));
+ #endif
+ 
  	    final_sequence = body;
  
  	    /* The first insn in this SEQUENCE might be a JUMP_INSN that will
Index: dwarf2out.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/dwarf2out.c,v
retrieving revision 1.423
diff -c -d -p -F^[(a-zA-Z0-9_^#] -r1.423 dwarf2out.c
*** dwarf2out.c	29 Apr 2003 20:42:55 -0000	1.423
--- dwarf2out.c	6 May 2003 16:57:10 -0000
*************** dwarf2out_frame_debug (insn)
*** 1685,1690 ****
--- 1685,1695 ----
        return;
      }
  
+   /* Ignore insns passed during a delayed-branch sequence.  Their effects
+      should have been described before the start of the sequence.  */
+   if (final_sequence != 0)
+     return;
+ 
    if (GET_CODE (insn) != INSN || clobbers_queued_reg_save (insn))
      flush_queued_reg_saves ();