Fix -fcompare-debug issue in purge_dead_edges [PR95080]

The following testcase fails with -fcompare-debug, the bug used to be latent
since introduction of -fcompare-debug.
The loop at the start of purge_dead_edges behaves differently between -g0
and -g - if the last insn is a DEBUG_INSN, then it skips not just
DEBUG_INSNs but also NOTEs until it finds some other real insn (or bb head),
while with -g0 it will not skip any NOTEs, so if we have
real_insn
note
debug_insn // not present with -g0
then with -g it might remove useless REG_EH_REGION from real_insn, while
with -g0 it will not.

Yet another option would be not skipping NOTE_P in the loop; I couldn't find
in history rationale for why it is done.

2020-05-13  Jakub Jelinek  <jakub@redhat.com>

	PR debug/95080
	* cfgrtl.c (purge_dead_edges): Skip over debug and note insns even
	if the last insn is a note.

	* g++.dg/opt/pr95080.C: New test.

4 files changed, 49 insertions, 1 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ba230b4..7fe1c6c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,9 @@
 2020-05-13  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/95080
+	* cfgrtl.c (purge_dead_edges): Skip over debug and note insns even
+	if the last insn is a note.
+
 	PR tree-optimization/95060
 	* tree-ssa-math-opts.c (convert_mult_to_fma_1): Fold a NEGATE_EXPR
 	if it is the single use of the FMA internal builtin.
diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
index e6ea687..827e84a 100644
--- a/gcc/cfgrtl.c
+++ b/gcc/cfgrtl.c
@@ -3100,7 +3100,7 @@ purge_dead_edges (basic_block bb)
   bool found;
   edge_iterator ei;
 
-  if (DEBUG_INSN_P (insn) && insn != BB_HEAD (bb))
+  if ((DEBUG_INSN_P (insn) || NOTE_P (insn)) && insn != BB_HEAD (bb))
     do
       insn = PREV_INSN (insn);
     while ((DEBUG_INSN_P (insn) || NOTE_P (insn)) && insn != BB_HEAD (bb));
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 02878c0..22adacb 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2020-05-13  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/95080
+	* g++.dg/opt/pr95080.C: New test.
+
 	PR tree-optimization/95060
 	* gcc.target/i386/avx512f-pr95060.c: New test.
 	* gcc.target/i386/fma_double_1.c: Adjust expected insn counts.
diff --git a/gcc/testsuite/g++.dg/opt/pr95080.C b/gcc/testsuite/g++.dg/opt/pr95080.C
new file mode 100644
index 0000000..2da7df7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr95080.C
@@ -0,0 +1,41 @@
+// PR debug/95080
+// { dg-do compile }
+// { dg-options "-Og -fcse-follow-jumps -fnon-call-exceptions -fcompare-debug" }
+
+char *a;
+
+void baz ();
+
+static inline bool
+bar ()
+{
+  int j = a[0] - 1;
+  switch (j)
+    {
+    case 0:
+    case 2:
+      return true;
+    default:
+      return false;
+    }
+}
+
+static inline bool
+foo ()
+{
+  if (bar ())
+    baz ();
+  return 0;
+}
+
+struct S
+{
+  int h;
+   ~S ();
+};
+
+S::~S ()
+{
+  if (a[0] == 0)
+    foo () != h;
+}