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.

gcc/ChangeLog

 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.
+
 	PR tree-optimization/94621
 	* tree-inline.c (remap_type_1): Don't dereference NULL TYPE_DOMAIN.
 	Move id->adjust_array_error_bounds check first in the condition.

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)
+  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));

gcc/testsuite/ChangeLog

 2020-04-17  Jakub Jelinek  <jakub@redhat.com>
 
+	PR rtl-optimization/94618
+	* g++.dg/opt/pr94618.C: New test.
+
 	PR tree-optimization/94621
 	* gcc.c-torture/compile/pr94621.c: New test.
 

gcc/testsuite/g++.dg/opt/pr94618.C

+// PR rtl-optimization/94618
+// { dg-do compile { target c++11 } }
+// { dg-options "-O2 -fnon-call-exceptions -fcompare-debug" }
+
+struct S
+{
+  int a, b, c;
+  int foo () noexcept { return a; }
+  int bar () noexcept { return b; }
+  void baz (int);
+  void qux () { if (c) for (int x = foo (); x != bar (); ) baz (x); }
+};
+
+struct T
+{
+  S s;
+  void foo ();
+};
+
+void
+T::foo ()
+{
+  s.qux ();
+  s.qux ();
+}