get emit_cmp_and_jump_insn_1 to mark the jump's label

[Alexandre Oliva <aoliva at redhat dot com>]

I ran into an interesting failure on this port I'm working on.  Loop
strength reduction decided to emit a mult_add, but the add was in a
wider mode than the machine supported directly, and had to be
synthesized.  It turned out that the carry of the lower-word addition
could only be obtained with branch-around-set, so we emitted a branch
without a JUMP_LABEL after the jump pass added those that were
missing, and we ended up crashing while constructing the flow graph.

This patch arranges for the jump instructions emitted by
emit_cmp_and_jump_insn_1 to have the JUMP_LABEL set in them.  It is
enough to fix the failure I was observing, but there might be other
situations in which we emit branches without setting their
JUMP_LABELs.

RTH and I agree that, ideally, we shouldn't need the jump pass to add
JUMP_LABELs that are missing, but it's not clear that this is anywhere
nearly feasible with a reasonable effort at the moment, so I'd like to
add this a stop gap.

What we don't agree is that this approach is ideal.  RTH seems to be
of the opinion that something along the lines of mark_jump_to_label
should scan a sequence of instructions that might have been passed to
emit_jump_insn, instead of simple-mindedly adding the JUMP_LABEL note
to the insn returned by emit_jump_insn, and only if it turns out to be
a JUMP_INSN.  My reasoning is that, if emit_jump_insn() takes a
sequence, the insns in the sequence must have been emitted before,
and, therefore, they should have already been emitted with
JUMP_LABELs, so scanning the seq would not only be inefficient, but
also hide latent bugs.

Anyone else willing to help me convince RTH? :-)

This patch was bootstrapped on i686-pc-linux-gnu, and tested on this
port I'm working on.  Ok to install?

Index: gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	* jump.c (mark_jump_to_label): New.
	* rtl.h (mark_jump_to_label): Declare it.
	* optabs.c (emit_cmp_and_jump_insn_1): Call it.

Index: gcc/jump.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/jump.c,v
retrieving revision 1.235
diff -u -p -r1.235 jump.c
--- gcc/jump.c 19 Jul 2003 14:47:07 -0000 1.235
+++ gcc/jump.c 22 Jul 2003 04:18:23 -0000
@@ -1345,6 +1345,16 @@ follow_jumps (rtx label)
 }
 
 
+/* If the given INSN is a JUMP_INSN, mark it as jumping to the givne LABEL.  */
+rtx
+mark_jump_to_label (rtx insn, rtx label)
+{
+  if (GET_CODE (insn) == JUMP_INSN)
+    JUMP_LABEL (insn) = label;
+
+  return insn;
+}
+
 /* Find all CODE_LABELs referred to in X, and increment their use counts.
    If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
    in INSN, then store one of them in JUMP_LABEL (INSN).
Index: gcc/rtl.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/rtl.h,v
retrieving revision 1.430
diff -u -p -r1.430 rtl.h
--- gcc/rtl.h 14 Jul 2003 21:18:14 -0000 1.430
+++ gcc/rtl.h 22 Jul 2003 04:18:25 -0000
@@ -1554,6 +1554,7 @@ extern enum rtx_code reverse_condition_m
 extern enum rtx_code swap_condition (enum rtx_code);
 extern enum rtx_code unsigned_condition (enum rtx_code);
 extern enum rtx_code signed_condition (enum rtx_code);
+extern rtx mark_jump_to_label (rtx, rtx);
 extern void mark_jump_label (rtx, rtx, int);
 extern void cleanup_barriers (void);
 
Index: gcc/optabs.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/optabs.c,v
retrieving revision 1.187
diff -u -p -r1.187 optabs.c
--- gcc/optabs.c 22 Jul 2003 00:36:52 -0000 1.187
+++ gcc/optabs.c 22 Jul 2003 04:18:27 -0000
@@ -3762,7 +3762,9 @@ emit_cmp_and_jump_insn_1 (rtx x, rtx y, 
 	    {
 	      x = prepare_operand (icode, x, 1, mode, wider_mode, unsignedp);
 	      y = prepare_operand (icode, y, 2, mode, wider_mode, unsignedp);
-	      emit_jump_insn (GEN_FCN (icode) (test, x, y, label));
+	      mark_jump_to_label
+		(emit_jump_insn (GEN_FCN (icode) (test, x, y, label)),
+		 label);
 	      return;
 	    }
 	}
@@ -3774,7 +3776,9 @@ emit_cmp_and_jump_insn_1 (rtx x, rtx y, 
 	  x = prepare_operand (icode, x, 0, mode, wider_mode, unsignedp);
 	  emit_insn (GEN_FCN (icode) (x));
 	  if (label)
-	    emit_jump_insn ((*bcc_gen_fctn[(int) comparison]) (label));
+	    mark_jump_to_label
+	      (emit_jump_insn ((*bcc_gen_fctn[(int) comparison]) (label)),
+	       label);
 	  return;
 	}
 
@@ -3787,7 +3791,9 @@ emit_cmp_and_jump_insn_1 (rtx x, rtx y, 
 	  y = prepare_operand (icode, y, 1, mode, wider_mode, unsignedp);
 	  emit_insn (GEN_FCN (icode) (x, y));
 	  if (label)
-	    emit_jump_insn ((*bcc_gen_fctn[(int) comparison]) (label));
+	    mark_jump_to_label
+	      (emit_jump_insn ((*bcc_gen_fctn[(int) comparison]) (label)),
+	       label);
 	  return;
 	}
 

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                 aoliva@{redhat.com, gcc.gnu.org}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist                Professional serial bug killer