[Committed] patch fixing LRA crash on s390x

[Vladimir Makarov <vmakarov@redhat.com>]

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My last patch implementing output reloads in asm goto resulted in LRA 
crash in compiling kernel on s390x.  Jeff Law reported it recently.  The 
culprit was in incorrect emitting reload insns in last empty BB.  The 
emitted insns got null BB which is wrong. Actually in this case we do 
not need to emit such insns as they will removed as dead lately.

The following patch fixes the problem.




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Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Sun Nov 15 11:22:19 2020 -0500

    Do not put reload insns in the last empty BB.
    
    gcc/
            * lra.c (lra_process_new_insns): Don't put reload insns in the
            last empty BB.

diff --git a/gcc/lra.c b/gcc/lra.c
index 673554d0a4b..b318cfd7456 100644
--- a/gcc/lra.c
+++ b/gcc/lra.c
@@ -1903,15 +1903,23 @@ lra_process_new_insns (rtx_insn *insn, rtx_insn *before, rtx_insn *after,
 	      {
 		/* We already made the edge no-critical in ira.c::ira */
 		lra_assert (!EDGE_CRITICAL_P (e));
-		rtx_insn *tmp = BB_HEAD (e->dest);
+		rtx_insn *curr, *tmp = BB_HEAD (e->dest);
 		if (LABEL_P (tmp))
 		  tmp = NEXT_INSN (tmp);
 		if (NOTE_INSN_BASIC_BLOCK_P (tmp))
 		  tmp = NEXT_INSN (tmp);
-		start_sequence ();
-		for (rtx_insn *curr = after;
-		     curr != NULL_RTX;
+		for (curr = tmp;
+		     curr != NULL
+		       && (!INSN_P (curr) || BLOCK_FOR_INSN (curr) == e->dest);
 		     curr = NEXT_INSN (curr))
+		  ;
+		/* Do not put reload insns if it is the last BB
+		   without actual insns.  In this case the reload insns
+		   can get null BB after emitting.  */
+		if (curr == NULL)
+		  continue;
+		start_sequence ();
+		for (curr = after; curr != NULL_RTX; curr = NEXT_INSN (curr))
 		  emit_insn (copy_insn (PATTERN (curr)));
 		rtx_insn *copy = get_insns (), *last = get_last_insn ();
 		end_sequence ();