RFC : Patch to make auto-increment generation more aggressive.

["Ramana Radhakrishnan" <ramana dot r at gmail dot com>]

Hi,

We could improve auto-increment for ports that have post modify or
post increment to generate better code with the attached patch.

Currently we disable post_inc generation for the following case.

*(a+c1)
a = a + c2

The attached patch transforms this (with the necessary checks) ofcourse to
a = a + c1
*(a+=(c2 - c1))

provided ofcourse that the data flow requirements and other machine
constraints are met.  I am currently bootstrapping and regression
testing this on x86-64-linux  .

It has some extra printf's but these will be cleared up before I
submit it finally.

cheers
Ramana




-- 
Ramana Radhakrishnan

Index: auto-inc-dec.c
===================================================================
RCS file: /srv/cvs/icera_gnu_tools/gnu-4.3/gcc/auto-inc-dec.c,v
retrieving revision 1.1.1.1.2.1
diff -a -u -r1.1.1.1.2.1 auto-inc-dec.c
--- auto-inc-dec.c	20 Jul 2007 12:33:08 -0000	1.1.1.1.2.1
+++ auto-inc-dec.c	12 Sep 2007 06:56:14 -0000
@@ -149,6 +149,9 @@
         becomes
 
            *(a += c) pre
+
+	  
+
 */
 #ifdef AUTO_INC_DEC
 
@@ -692,12 +695,64 @@
     [inc_insn.reg1_state][mem_insn.reg1_state][inc_insn.form];
 
   if (dbg_cnt (auto_inc_dec) == false)
-    return false;
+      return false;
+
+  if (inc_insn.form == FORM_POST_INC &&
+      mem_insn.reg1_is_const &&
+      inc_insn.reg1_is_const && 
+      (mem_insn.reg1_val != inc_insn.reg1_val)
+	       && (mem_insn.reg1_val != -inc_insn.reg1_val))
+    {
+	/* This is the form where you have :
+	 * mem_insn of the form 
+	 *   * ( a + const1) = something
+	 *   a = a + const2 
+	 *   Transform this to 
+	 *   a = a + const1
+	 *   * ( a += const2 - const1)
+	 */
+ 	if (attempt_change (gen_rtx_POST_MODIFY (Pmode,
+						  inc_reg,
+						  plus_constant(inc_reg, inc_insn.reg1_val - 
+									mem_insn.reg1_val)),
+			     inc_reg))
+	  {
+	    	rtx insn;
+		int regno;
+		if (dump_file)
+		  fprintf (dump_file, "Attempting to change over\n");
+		/* We still have to emit an additional add before the mem insn
+		   and delete the inc insn. The lower inc insn is deleted
+		   in attempt_change already. Here we just set up the
+		   additional add instruction. 
+		*/
+		
+	//	insn = emit_insn_before (gen_rtx_SET ( Pmode, inc_reg, gen_rtx_PLUS ( Pmode, inc_reg, 
+	//					 mem_insn.reg1)), mem_insn.insn);
+	
+	
+		insn = emit_insn_before (gen_rtx_SET ( Pmode, inc_reg, plus_constant(inc_reg, 
+						 mem_insn.reg1_val)), mem_insn.insn);
+		regno = REGNO (inc_reg);
+	      	reg_next_def[regno] = insn;
+      		reg_next_use[regno] = mem_insn.insn;
+		reg_next_inc_use[regno] = insn;
+		df_recompute_luids (BASIC_BLOCK (BLOCK_NUM (mem_insn.insn)));
+
+		return true;
+	  }
+	else
+	  {
+	    return false;
+	  }
+    }
 
   switch (gen_form)
     {
     default:
     case NOTHING:
+      if (dump_file)
+	fprintf (dump_file, "try_merge gen_form is nothing\n");
       return false;
 
     case SIMPLE_PRE_INC:     /* ++size  */
@@ -1016,7 +1071,11 @@
     }
 
   if (dump_file)
-    dump_mem_insn (dump_file);
+    {
+      fprintf (dump_file, "From find_inc\n");
+      dump_mem_insn (dump_file);
+      fprintf (dump_file, "End of marker find inc1\n");
+    }
 
   /* Find the next use that is an inc.  */
   insn = get_next_ref (REGNO (mem_insn.reg0), 
@@ -1069,8 +1128,12 @@
     }
 
   if (dump_file)
-    dump_inc_insn (dump_file);
-
+    {
+     fprintf (dump_file, "Find inc marker dump_inc_insn #1\n");
+     dump_inc_insn (dump_file);
+     fprintf (dump_file, "End Find inc marker dump_inc_insn #1\n");
+    }
+	
   if (inc_insn.form == FORM_POST_ADD)
     {
       /* Make sure that there is no insn that assigns to inc_insn.res
@@ -1151,9 +1214,14 @@
 	}
       /* Both the inc/add and the mem have a constant.  Need to check
 	 that the constants are ok. */
-      else if ((mem_insn.reg1_val != inc_insn.reg1_val)
+      else if ((inc_insn.form != FORM_POST_INC) && 
+	       (mem_insn.reg1_val != inc_insn.reg1_val)
 	       && (mem_insn.reg1_val != -inc_insn.reg1_val))
-	return false;
+	{
+	  if (dump_file)
+	  	fprintf (dump_file, "Returning false because constants are not equal\n");
+	  return false;
+	}
     }
   else
     {
@@ -1278,9 +1346,14 @@
 	 in this form, we need to make sure that there
 	 were no intervening uses of reg.  */
       if (inc_insn.insn != other_insn)
-	return false;
+	{
+	  if (dump_file)
+	    fprintf (dump_file, "not the other insn\n");
+	  return false;	
+	}
     }
-
+  if (dump_file)
+    fprintf (dump_file, " to try merge\n");
   return try_merge ();
 }
 
@@ -1425,7 +1498,11 @@
 		    }
 		  
 		  if (dump_file)
+		    {
 		    dump_inc_insn (dump_file);
+		    if (dump_file)
+		      fprintf (dump_file, "ok is %s\n", ok? "true":"false");
+		    }
 		  
 		  if (ok && find_address (&PATTERN (mem_insn.insn)) == -1)
 		    {