[PATCH] Fix PR middle-end/80707, ICE: r247844 causes error: extra outgoing edge

[Peter Bergner]

My fix for PR51513 modified group_case_labels_stmt() to remove unreachable
case statements labels.  Being a middle-end newbie, I incorrectly thought
group_case_labels_stmt() was only called very early, before we have a cfg.
With -O3, we can generate extra copies of the switch statement, well after
the cfg exists, and we end up calling group_case_labels_stmt() to optimize
them.  In those cases, we need to remove their edges from the cfg.

This passes my bootstrap and regtesting on powerpc64le-linux and x86_64-linux
with no regressions.  In addition, both David and HJ confirm this fixes the
bootstrap issues they ran into.

Is this ok for trunk?

Peter

gcc/
        PR middle-end/80707
        * tree-cfg.c: Remove cfg edges of unreachable case statements.

gcc/testsuite/
        * g++.dg/pr80707.C: New test.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c      (revision 247845)
+++ gcc/tree-cfg.c      (working copy)
@@ -1684,6 +1684,10 @@ group_case_labels_stmt (gswitch *stmt)
          || (EDGE_COUNT (base_bb->succs) == 0
              && gimple_seq_unreachable_p (bb_seq (base_bb))))
        {
+         edge e;
+         if (base_bb != default_bb
+             && (e = find_edge (gimple_bb (stmt), base_bb)) != NULL)
+           remove_edge_and_dominated_blocks (e);
          gimple_switch_set_label (stmt, i, NULL_TREE);
          i++;
          new_size--;
Index: gcc/testsuite/g++.dg/pr80707.C
===================================================================
--- gcc/testsuite/g++.dg/pr80707.C      (nonexistent)
+++ gcc/testsuite/g++.dg/pr80707.C      (working copy)
@@ -0,0 +1,29 @@
+// PR middle-end/80707 ICE: extra outgoing edge causes verify_flow_info error.
+// { dg-do compile }
+// { dg-options "-O3" } */
+
+struct A {
+  int m_fn1(int &) const;
+};
+int A::m_fn1(int &p1) const {
+  int a[6];
+  int b = 0;
+  for (int i;; i++) {
+    if (a[i])
+      break;
+    b++;
+  }
+  while (b) {
+    int c;
+    switch (b) {
+    case 1:
+      c = 0;
+      break;
+    case 5:
+      c = a[0];
+    }
+    if (c)
+      p1 = 0;
+    b--;
+  }
+}