final.c (shorten_branches): When optimizing...

        * final.c (shorten_branches): When optimizing, start with small
        length and increase from there, and don't decrease lengths.

Co-Authored-By: Richard Sandiford <rdsandiford@googlemail.com>

From-SVN: r192634

gcc/ChangeLog

@@ -7,6 +7,9 @@
 	(steal_delay_list_from_target): Use copy_delay_slot_insn.
 	(fill_slots_from_thread, fill_simple_delay_slots): Likewise.
 
+	* final.c (shorten_branches): When optimizing, start with small
+	length and increase from there, and don't decrease lengths.
+
 2012-10-19  Jan Hubicka  <jh@suse.cz>
 
 	* builtins.def (BUILT_IN_UNREACHABLE): Make ATTR_CONST_NORETURN_NOTHROW_LEAF_LIST.

gcc/final.c

@@ -1009,6 +1009,13 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 	    align_tab[i] = seq;
 	}
     }
+
+  /* When optimizing, we start assuming minimum length, and keep increasing
+     lengths as we find the need for this, till nothing changes.
+     When not optimizing, we start assuming maximum lengths, and
+     do a single pass to update the lengths.  */
+  bool increasing = optimize != 0;
+
 #ifdef CASE_VECTOR_SHORTEN_MODE
   if (optimize)
     {
@@ -1062,11 +1069,16 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 	  flags.min_after_base = min > rel;
 	  flags.max_after_base = max > rel;
 	  ADDR_DIFF_VEC_FLAGS (pat) = flags;
+
+	  if (increasing)
+	    PUT_MODE (pat, CASE_VECTOR_SHORTEN_MODE (0, 0, pat));
 	}
     }
 #endif /* CASE_VECTOR_SHORTEN_MODE */
 
   /* Compute initial lengths, addresses, and varying flags for each insn.  */
+  int (*length_fun) (rtx) = increasing ? insn_min_length : insn_default_length;
+
   for (insn_current_address = 0, insn = first;
        insn != 0;
        insn_current_address += insn_lengths[uid], insn = NEXT_INSN (insn))
@@ -1117,6 +1129,8 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 #else
 	  const_delay_slots = 0;
 #endif
+	  int (*inner_length_fun) (rtx)
+	    = const_delay_slots ? length_fun : insn_default_length;
 	  /* Inside a delay slot sequence, we do not do any branch shortening
 	     if the shortening could change the number of delay slots
 	     of the branch.  */
@@ -1131,7 +1145,7 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 		inner_length = (asm_insn_count (PATTERN (inner_insn))
 				* insn_default_length (inner_insn));
 	      else
-		inner_length = insn_default_length (inner_insn);
+		inner_length = inner_length_fun (inner_insn);
 
 	      insn_lengths[inner_uid] = inner_length;
 	      if (const_delay_slots)
@@ -1149,7 +1163,7 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 	}
       else if (GET_CODE (body) != USE && GET_CODE (body) != CLOBBER)
 	{
-	  insn_lengths[uid] = insn_default_length (insn);
+	  insn_lengths[uid] = length_fun (insn);
 	  varying_length[uid] = insn_variable_length_p (insn);
 	}
 
@@ -1220,6 +1234,7 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 	      rtx prev;
 	      int rel_align = 0;
 	      addr_diff_vec_flags flags;
+	      enum machine_mode vec_mode;
 
 	      /* Avoid automatic aggregate initialization.  */
 	      flags = ADDR_DIFF_VEC_FLAGS (body);
@@ -1298,9 +1313,12 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 		  else
 		    max_addr += align_fuzz (max_lab, rel_lab, 0, 0);
 		}
-	      PUT_MODE (body, CASE_VECTOR_SHORTEN_MODE (min_addr - rel_addr,
-							max_addr - rel_addr,
-							body));
+	      vec_mode = CASE_VECTOR_SHORTEN_MODE (min_addr - rel_addr,
+						   max_addr - rel_addr, body);
+	      if (!increasing
+		  || (GET_MODE_SIZE (vec_mode)
+		      >= GET_MODE_SIZE (GET_MODE (body))))
+		PUT_MODE (body, vec_mode);
 	      if (JUMP_TABLES_IN_TEXT_SECTION
 		  || readonly_data_section == text_section)
 		{
@@ -1362,10 +1380,15 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 
 		  if (inner_length != insn_lengths[inner_uid])
 		    {
-		      insn_lengths[inner_uid] = inner_length;
-		      something_changed = 1;
+		      if (!increasing || inner_length > insn_lengths[inner_uid])
+			{
+			  insn_lengths[inner_uid] = inner_length;
+			  something_changed = 1;
+			}
+		      else
+			inner_length = insn_lengths[inner_uid];
 		    }
-		  insn_current_address += insn_lengths[inner_uid];
+		  insn_current_address += inner_length;
 		  new_length += inner_length;
 		}
 	    }
@@ -1382,14 +1405,17 @@ shorten_branches (rtx first ATTRIBUTE_UNUSED)
 	  insn_current_address += (new_length - tmp_length);
 #endif
 
-	  if (new_length != insn_lengths[uid])
+	  if (new_length != insn_lengths[uid]
+	      && (!increasing || new_length > insn_lengths[uid]))
 	    {
 	      insn_lengths[uid] = new_length;
 	      something_changed = 1;
 	    }
+	  else
+	    insn_current_address += insn_lengths[uid] - new_length;
 	}
       /* For a non-optimizing compile, do only a single pass.  */
-      if (!optimize)
+      if (!increasing)
 	break;
     }