[gcc(refs/vendors/redhat/heads/gcc-8-branch)] Fix -fcompare-debug issue in purge_dead_edges [PR95080]

[gcc(refs/vendors/redhat/heads/gcc-8-branch)] Fix -fcompare-debug issue in purge_dead_edges [PR95080]

[Jakub Jelinek]

https://gcc.gnu.org/g:3863112b91d354f0a028e806cfe2678c8552b051

commit 3863112b91d354f0a028e806cfe2678c8552b051
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 13 11:22:37 2020 +0200

    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.
    
    (cherry picked from commit 18edc195442291525e04f0fa4d5ef972155117da)

Diff:
---
 gcc/cfgrtl.c                       |  2 +-
 gcc/testsuite/g++.dg/opt/pr95080.C | 41 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
index d15f94ec6dc..261aa5078e7 100644
--- a/gcc/cfgrtl.c
+++ b/gcc/cfgrtl.c
@@ -3051,7 +3051,7 @@ 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/g++.dg/opt/pr95080.C b/gcc/testsuite/g++.dg/opt/pr95080.C
new file mode 100644
index 00000000000..2da7df73b72
--- /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;
+}