[backport proposed but not yet approved or applied fix for gcc-4.9/trunk <mikpe@it.uu.se>]

List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>
From: Eric Botcazou <ebotcazou at adacore dot com>
Subject: Fill more delay slots in conditional returns
Date: Mon, 25 Mar 2013 12:25:57 +0100

Hi,

for a private port with conditional returns and delay slots, only the simple 
algorithm (fill_simple_delay_slots) is able to fill the slots.  It's because 
get_branch_condition just punts on conditional returns.

Fixed thusly.  While I investigated this, I realized that the block of code in 
fill_simple_delay_slots between line 2097 and line 2274 is dead for JUMP insns 
(and has been so for a long time, which is consistent with various comments in 
the code, for example the head comment of fill_eager_delay_slots) so the patch 
also cleans it up (modulo the formatting to make the patch readable).

Jeff, any objections?  Tested on SPARC/Solaris, no difference in the generated 
code at -O2 for the gcc.c-torture/compile testsuite.


2013-03-25  Eric Botcazou  <ebotcazou@adacore.com>

	* reorg.c (get_branch_condition): Deal with conditional returns.
	(fill_simple_delay_slots): Remove dead code dealing with jumps.

--- gcc-4.8.0/gcc/reorg.c.~1~	2013-01-10 21:38:27.000000000 +0100
+++ gcc-4.8.0/gcc/reorg.c	2013-03-29 14:12:18.451590316 +0100
@@ -921,8 +921,8 @@ get_branch_condition (rtx insn, rtx targ
   if (condjump_in_parallel_p (insn))
     pat = XVECEXP (pat, 0, 0);
 
-  if (ANY_RETURN_P (pat))
-    return pat == target ? const_true_rtx : 0;
+  if (ANY_RETURN_P (pat) && pat == target)
+    return const_true_rtx;
 
   if (GET_CODE (pat) != SET || SET_DEST (pat) != pc_rtx)
     return 0;
@@ -933,14 +933,16 @@ get_branch_condition (rtx insn, rtx targ
 
   else if (GET_CODE (src) == IF_THEN_ELSE
 	   && XEXP (src, 2) == pc_rtx
-	   && GET_CODE (XEXP (src, 1)) == LABEL_REF
-	   && XEXP (XEXP (src, 1), 0) == target)
+	   && ((GET_CODE (XEXP (src, 1)) == LABEL_REF
+	        && XEXP (XEXP (src, 1), 0) == target)
+	       || (ANY_RETURN_P (XEXP (src, 1)) && XEXP (src, 1) == target)))
     return XEXP (src, 0);
 
   else if (GET_CODE (src) == IF_THEN_ELSE
 	   && XEXP (src, 1) == pc_rtx
-	   && GET_CODE (XEXP (src, 2)) == LABEL_REF
-	   && XEXP (XEXP (src, 2), 0) == target)
+	   && ((GET_CODE (XEXP (src, 2)) == LABEL_REF
+		&& XEXP (XEXP (src, 2), 0) == target)
+	       || (ANY_RETURN_P (XEXP (src, 2)) && XEXP (src, 2) == target)))
     {
       enum rtx_code rev;
       rev = reversed_comparison_code (XEXP (src, 0), insn);
@@ -2129,35 +2131,19 @@ fill_simple_delay_slots (int non_jumps_p
 	     Presumably, we should also check to see if we could get
 	     back to this function via `setjmp'.  */
 	  && ! can_throw_internal (insn)
-	  && (!JUMP_P (insn)
-	      || ((condjump_p (insn) || condjump_in_parallel_p (insn))
-		  && ! simplejump_p (insn)
-		  && !ANY_RETURN_P (JUMP_LABEL (insn)))))
+	  && !JUMP_P (insn))
 	{
-	  /* Invariant: If insn is a JUMP_INSN, the insn's jump
-	     label.  Otherwise, zero.  */
-	  rtx target = 0;
 	  int maybe_never = 0;
 	  rtx pat, trial_delay;
 
 	  CLEAR_RESOURCE (&needed);
 	  CLEAR_RESOURCE (&set);
+	  mark_set_resources (insn, &set, 0, MARK_SRC_DEST_CALL);
+	  mark_referenced_resources (insn, &needed, true);
 
 	  if (CALL_P (insn))
-	    {
-	      mark_set_resources (insn, &set, 0, MARK_SRC_DEST_CALL);
-	      mark_referenced_resources (insn, &needed, true);
-	      maybe_never = 1;
-	    }
-	  else
-	    {
-	      mark_set_resources (insn, &set, 0, MARK_SRC_DEST_CALL);
-	      mark_referenced_resources (insn, &needed, true);
-	      if (JUMP_P (insn))
-		target = JUMP_LABEL (insn);
-	    }
+	    maybe_never = 1;
 
-	  if (target == 0 || ANY_RETURN_P (target))
 	    for (trial = next_nonnote_insn (insn); !stop_search_p (trial, 1);
 		 trial = next_trial)
 	      {
@@ -2217,9 +2203,8 @@ fill_simple_delay_slots (int non_jumps_p
 		   slot since these insns could clobber the condition code.  */
 		set.cc = 1;
 
-		/* If this is a call or jump, we might not get here.  */
-		if (CALL_P (trial_delay)
-		    || JUMP_P (trial_delay))
+		/* If this is a call, we might not get here.  */
+		if (CALL_P (trial_delay))
 		  maybe_never = 1;
 	      }
 
@@ -2232,7 +2217,6 @@ fill_simple_delay_slots (int non_jumps_p
 	      && trial
 	      && jump_to_label_p (trial)
 	      && simplejump_p (trial)
-	      && (target == 0 || JUMP_LABEL (trial) == target)
 	      && (next_trial = next_active_insn (JUMP_LABEL (trial))) != 0
 	      && ! (NONJUMP_INSN_P (next_trial)
 		    && GET_CODE (PATTERN (next_trial)) == SEQUENCE)
@@ -2264,11 +2248,6 @@ fill_simple_delay_slots (int non_jumps_p
 					 delay_list);
 		  slots_filled++;
 		  reorg_redirect_jump (trial, new_label);
-
-		  /* If we merged because we both jumped to the same place,
-		     redirect the original insn also.  */
-		  if (target)
-		    reorg_redirect_jump (insn, new_label);
 		}
 	    }
 	}