[PATCH/RFC] Fix PR optimization/15100

[Kaz Kojima]

amylaar@spamcop.net (Joern Rennecke) wrote:
> So, your patch works, but it's not immediately apparent from the code
> why it works.  The && place is a red herring.
> 
> I think something like this would be clearer:
> 
> 	      /* If the insn carrying the REG_LIBCALL (*) note has been marked
> 		 as NOTE_INSN_DELETED, find_reg_note returns NULL_RTX.  */
> 	      if (! tem)
> 		/* We're deleting either the last remaining instruction of a
> 		   libcall sequence, or we are deleting both the first and
> 		   the last instruction of a libcall sequence.  In the latter
> 		   case, none of the remaining insns (if any) of the libcall
> 		   computes a libcall value, so they do not belong in a libcall
> 		   sequence.  Thus, drop the notes.  */
> 		place = 0;
> 		/* Since the other side of the libcall still exists, there must
> 		   be at least on insn left in that direction.  */
> 	     else if (! place)
> 	       abort ()
> 	     else XEXP (tem, 0) = place;
> 	     
> (*): Use REG_RETVAL in the REG_LIBCALL case.

Looks cleaner and more descriptive.  I run make bootstrap for 3.4.0
on i686-linux with the patch below and found no problems in regtest.
There are no regressions on x86-linux cross to sh4-linux with it and
I'll test it on native sh-linux too.  For mainline, it would be better
to revisit this after the merges from tree-ssa settled.  I guess that
the last patch might be enough for 3.4-branch.  There were no complains
from targets other than SH on 3.4-branch about the current behavior
of distribute_notes and that patch seems hard to affect the cases
which are currently working.

Regards,
	kaz
--
diff -uprN ORIG/gcc-3.4.0/gcc/combine.c LOCAL/gcc-3.4.0/gcc/combine.c
--- ORIG/gcc-3.4.0/gcc/combine.c	2004-02-21 22:24:43.000000000 +0900
+++ LOCAL/gcc-3.4.0/gcc/combine.c	2004-05-13 10:45:21.000000000 +0900
@@ -12582,12 +12582,22 @@ distribute_notes (rtx notes, rtx from_in
 	    {
 	      tem = find_reg_note (XEXP (note, 0), REG_LIBCALL, NULL_RTX);
 	      place = prev_real_insn (from_insn);
-	      if (tem && place)
+	      /* If the insn carrying the REG_LIBCALL note has been marked
+		 as NOTE_INSN_DELETED, find_reg_note returns NULL_RTX.  */
+	      if (! tem)
+		/* We're deleting either the last remaining instruction of
+		   a libcall sequence, or we are deleting both the first and
+		   the last instruction of a libcall sequence.  In the latter
+		   case, none of the remaining insns (if any) of the libcall
+		   computes a libcall value, so they do not belong in a
+		   libcall sequence.  Thus, drop the notes.  */
+		place = 0;
+	      else if (! place)
+		/* Since the other side of the libcall still exists, there
+		   must be at least on insn left in that direction.  */
+		abort ();
+	      else
 		XEXP (tem, 0) = place;
-	      /* If we're deleting the last remaining instruction of a
-		 libcall sequence, don't add the notes.  */
-	      else if (XEXP (note, 0) == from_insn)
-		tem = place = 0;
 	    }
 	  break;
 
@@ -12599,12 +12609,22 @@ distribute_notes (rtx notes, rtx from_in
 	    {
 	      tem = find_reg_note (XEXP (note, 0), REG_RETVAL, NULL_RTX);
 	      place = next_real_insn (from_insn);
-	      if (tem && place)
+	      /* If the insn carrying the REG_RETVAL note has been marked
+		 as NOTE_INSN_DELETED, find_reg_note returns NULL_RTX.  */
+	      if (! tem)
+		/* We're deleting either the last remaining instruction of
+		   a libcall sequence, or we are deleting both the first and
+		   the last instruction of a libcall sequence.  In the latter
+		   case, none of the remaining insns (if any) of the libcall
+		   computes a libcall value, so they do not belong in a
+		   libcall sequence.  Thus, drop the notes.  */
+		place = 0;
+	      else if (! place)
+		/* Since the other side of the libcall still exists, there
+		   must be at least on insn left in that direction.  */
+		abort ();
+	      else
 		XEXP (tem, 0) = place;
-	      /* If we're deleting the last remaining instruction of a
-		 libcall sequence, don't add the notes.  */
-	      else if (XEXP (note, 0) == from_insn)
-		tem = place = 0;
 	    }
 	  break;