re PR target/39942 (Nonoptimal code - leaveq; xchg %ax,%ax; retq)

	PR target/39942
	* final.c (label_to_max_skip): New function.
	(label_to_alignment): Only use LABEL_TO_ALIGNMENT if
	CODE_LABEL_NUMBER <= max_labelno.
	* output.h (label_to_max_skip): New prototype.
	* config/i386/i386.c (ix86_avoid_jump_misspredicts): Renamed to...
	(ix86_avoid_jump_mispredicts): ... this.  Don't define if
	ASM_OUTPUT_MAX_SKIP_ALIGN isn't defined.  Update comment.
	Handle CODE_LABELs with >= 16 byte alignment or with
	max_skip == (1 << align) - 1.
	(ix86_reorg): Don't call ix86_avoid_jump_mispredicts if
	ASM_OUTPUT_MAX_SKIP_ALIGN isn't defined.

From-SVN: r147607

gcc/ChangeLog

 2009-05-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/39942
+	* final.c (label_to_max_skip): New function.
+	(label_to_alignment): Only use LABEL_TO_ALIGNMENT if
+	CODE_LABEL_NUMBER <= max_labelno.
+	* output.h (label_to_max_skip): New prototype.
+	* config/i386/i386.c (ix86_avoid_jump_misspredicts): Renamed to...
+	(ix86_avoid_jump_mispredicts): ... this.  Don't define if
+	ASM_OUTPUT_MAX_SKIP_ALIGN isn't defined.  Update comment.
+	Handle CODE_LABELs with >= 16 byte alignment or with
+	max_skip == (1 << align) - 1.
+	(ix86_reorg): Don't call ix86_avoid_jump_mispredicts if
+	ASM_OUTPUT_MAX_SKIP_ALIGN isn't defined.
+
+	PR target/39942
 	* config/i386/x86-64.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Don't emit second
 	.p2align 3 if MAX_SKIP is smaller than 7.
 	* config/i386/linux.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Likewise.

gcc/config/i386/i386.c

@@ -27191,6 +27191,7 @@ x86_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED)
     }
 }
 
+#ifdef ASM_OUTPUT_MAX_SKIP_ALIGN
 /* We don't have exact information about the insn sizes, but we may assume
    quite safely that we are informed about all 1 byte insns and memory
    address sizes.  This is enough to eliminate unnecessary padding in
@@ -27241,7 +27242,7 @@ min_insn_size (rtx insn)
    window.  */
 
 static void
-ix86_avoid_jump_misspredicts (void)
+ix86_avoid_jump_mispredicts (void)
 {
   rtx insn, start = get_insns ();
   int nbytes = 0, njumps = 0;
@@ -27255,15 +27256,52 @@ ix86_avoid_jump_misspredicts (void)
 
      The smallest offset in the page INSN can start is the case where START
      ends on the offset 0.  Offset of INSN is then NBYTES - sizeof (INSN).
-     We add p2align to 16byte window with maxskip 17 - NBYTES + sizeof (INSN).
+     We add p2align to 16byte window with maxskip 15 - NBYTES + sizeof (INSN).
      */
-  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
+  for (insn = start; insn; insn = NEXT_INSN (insn))
     {
+      int min_size;
 
-      nbytes += min_insn_size (insn);
+      if (GET_CODE (insn) == CODE_LABEL)
+	{
+	  int align = label_to_alignment (insn);
+	  int max_skip = label_to_max_skip (insn);
+
+	  if (max_skip > 15)
+	    max_skip = 15;
+	  /* If align > 3, only up to 16 - max_skip - 1 bytes can be
+	     already in the current 16 byte page, because otherwise
+	     ASM_OUTPUT_MAX_SKIP_ALIGN could skip max_skip or fewer
+	     bytes to reach 16 byte boundary.  */
+	  if (align <= 0
+	      || (align <= 3 && max_skip != (1 << align) - 1))
+	    max_skip = 0;
+	  if (dump_file)
+	    fprintf (dump_file, "Label %i with max_skip %i\n",
+		     INSN_UID (insn), max_skip);
+	  if (max_skip)
+	    {
+	      while (nbytes + max_skip >= 16)
+		{
+		  start = NEXT_INSN (start);
+		  if ((JUMP_P (start)
+		       && GET_CODE (PATTERN (start)) != ADDR_VEC
+		       && GET_CODE (PATTERN (start)) != ADDR_DIFF_VEC)
+		      || CALL_P (start))
+		    njumps--, isjump = 1;
+		  else
+		    isjump = 0;
+		  nbytes -= min_insn_size (start);
+		}
+	    }
+	  continue;
+	}
+
+      min_size = min_insn_size (insn);
+      nbytes += min_size;
       if (dump_file)
-        fprintf(dump_file, "Insn %i estimated to %i bytes\n",
-		INSN_UID (insn), min_insn_size (insn));
+	fprintf (dump_file, "Insn %i estimated to %i bytes\n",
+		 INSN_UID (insn), min_size);
       if ((JUMP_P (insn)
 	   && GET_CODE (PATTERN (insn)) != ADDR_VEC
 	   && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC)
@@ -27287,7 +27325,7 @@ ix86_avoid_jump_misspredicts (void)
       gcc_assert (njumps >= 0);
       if (dump_file)
         fprintf (dump_file, "Interval %i to %i has %i bytes\n",
-		INSN_UID (start), INSN_UID (insn), nbytes);
+		 INSN_UID (start), INSN_UID (insn), nbytes);
 
       if (njumps == 3 && isjump && nbytes < 16)
 	{
@@ -27300,6 +27338,7 @@ ix86_avoid_jump_misspredicts (void)
 	}
     }
 }
+#endif
 
 /* AMD Athlon works faster
    when RET is not destination of conditional jump or directly preceded
@@ -27363,8 +27402,10 @@ ix86_reorg (void)
     {
       if (TARGET_PAD_RETURNS)
 	ix86_pad_returns ();
+#ifdef ASM_OUTPUT_MAX_SKIP_ALIGN
       if (TARGET_FOUR_JUMP_LIMIT)
-	ix86_avoid_jump_misspredicts ();
+	ix86_avoid_jump_mispredicts ();
+#endif
     }
 }
 

gcc/final.c

@@ -553,7 +553,17 @@ static int min_labelno, max_labelno;
 int
 label_to_alignment (rtx label)
 {
-  return LABEL_TO_ALIGNMENT (label);
+  if (CODE_LABEL_NUMBER (label) <= max_labelno)
+    return LABEL_TO_ALIGNMENT (label);
+  return 0;
+}
+
+int
+label_to_max_skip (rtx label)
+{
+  if (CODE_LABEL_NUMBER (label) <= max_labelno)
+    return LABEL_TO_MAX_SKIP (label);
+  return 0;
 }
 
 #ifdef HAVE_ATTR_length

gcc/output.h

 /* Declarations for insn-output.c.  These functions are defined in recog.c,
    final.c, and varasm.c.
    Copyright (C) 1987, 1991, 1994, 1997, 1998, 1999, 2000, 2001, 2002,
-   2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
+   2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -94,6 +94,10 @@ extern int insn_current_reference_address (rtx);
    Defined in final.c.  */
 extern int label_to_alignment (rtx);
 
+/* Find the alignment maximum skip associated with a CODE_LABEL.
+   Defined in final.c.  */
+extern int label_to_max_skip (rtx);
+
 /* Output a LABEL_REF, or a bare CODE_LABEL, as an assembler symbol.  */
 extern void output_asm_label (rtx);