Fix -fcompare-debug issue in delete_insn_and_edges [PR94618]

delete_insn_and_edges calls purge_dead_edges whenever deleting the last insn
in a bb, whatever it is.  If it called it only for mandatory last insns
in the basic block (that may not be followed by DEBUG_INSNs, dunno if that
is control_flow_insn_p or something more complex), that wouldn't be a
problem, but as it calls it on any last insn and can actually do something
in the bb, if such an insn is followed by one more more DEBUG_INSNs and
nothing else in the same bb, we don't call purge_dead_edges with -g and do
call it with -g0.

On the testcase, there are two reg-to-reg moves with REG_EH_REGION notes
(previously memory accesses but simplified and yet not optimized), and the
second is followed by DEBUG_INSNs; the second move is delete_insn_and_edges
and after removing it, for -g0 purge_dead_edges removes the REG_EH_REGION
from the now last insn in the bb (the first reg-to-reg move), while
for -g it isn't called and things diverge from that quickly on.

Fixed by calling purdge_dead_edges even if we remove the last real insn
followed only by DEBUG_INSNs in the same bb.

2020-04-17  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/94618
	* cfgrtl.c (delete_insn_and_edges): Set purge not just when
	insn is the BB_END of its block, but also when it is only followed
	by DEBUG_INSNs in its block.

	* g++.dg/opt/pr94618.C: New test.

1 files changed, 14 insertions, 4 deletions

diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
index fb551e3..e6ea687 100644
--- a/gcc/cfgrtl.c
+++ b/gcc/cfgrtl.c
@@ -230,10 +230,20 @@ delete_insn_and_edges (rtx_insn *insn)
 {
   bool purge = false;
 
-  if (INSN_P (insn)
-      && BLOCK_FOR_INSN (insn)
-      && BB_END (BLOCK_FOR_INSN (insn)) == insn)
-    purge = true;
+  if (INSN_P (insn) && BLOCK_FOR_INSN (insn))
+    {
+      basic_block bb = BLOCK_FOR_INSN (insn);
+      if (BB_END (bb) == insn)
+	purge = true;
+      else if (DEBUG_INSN_P (BB_END (bb)))
+	for (rtx_insn *dinsn = NEXT_INSN (insn);
+	     DEBUG_INSN_P (dinsn); dinsn = NEXT_INSN (dinsn))
+	  if (BB_END (bb) == dinsn)
+	    {
+	      purge = true;
+	      break;
+	    }
+    }
   delete_insn (insn);
   if (purge)
     return purge_dead_edges (BLOCK_FOR_INSN (insn));