Revert r263947.

2018-10-22  Martin Liska  <mliska@suse.cz>

  PR tree-optimization/87686
	Revert
	2018-08-29  Martin Liska  <mliska@suse.cz>

	* tree-switch-conversion.c (switch_conversion::expand):
	Strenghten assumption about gswitch statements.
2018-10-22  Martin Liska  <mliska@suse.cz>

  PR tree-optimization/87686
	* g++.dg/tree-ssa/pr87686.C: New test.

From-SVN: r265388

gcc/ChangeLog

@@ -1,3 +1,12 @@
+2018-10-22  Martin Liska  <mliska@suse.cz>
+
+  PR tree-optimization/87686
+	Revert
+	2018-08-29  Martin Liska  <mliska@suse.cz>
+
+	* tree-switch-conversion.c (switch_conversion::expand):
+	Strenghten assumption about gswitch statements.
+
 2018-10-22  Martin Liska  <mliska@suse.cz>
 
 	* ipa-icf.c (sem_item::compare_attributes): Remove.

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2018-10-22  Martin Liska  <mliska@suse.cz>
+
+  PR tree-optimization/87686
+	* g++.dg/tree-ssa/pr87686.C: New test.
+
 2018-10-22  Jakub Jelinek  <jakub@redhat.com>
 
 	* g++.target/i386/i386.exp: Use g++-dg-runtest to iterate

gcc/testsuite/g++.dg/tree-ssa/pr87686.C

@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+class a {
+public:
+  enum b { c, g, d, e } f;
+  a(b h) : f(h) {}
+  a i() {
+    switch (f) {
+    case d:
+      return c;
+    case e:
+      return g;
+    }
+  } /* { dg-warning "control reaches end of non-void function" } */
+};
+struct k {
+  a j;
+  k l() { j.i(); } /*  { dg-warning "no return statement in function returning non-void" } */
+};
+void m(k h) { h.l(); }

gcc/tree-switch-conversion.c

@@ -913,7 +913,14 @@ switch_conversion::expand (gswitch *swtch)
   /* Group case labels so that we get the right results from the heuristics
      that decide on the code generation approach for this switch.  */
   m_cfg_altered |= group_case_labels_stmt (swtch);
-  gcc_assert (gimple_switch_num_labels (swtch) >= 2);
+
+  /* If this switch is now a degenerate case with only a default label,
+     there is nothing left for us to do.  */
+  if (gimple_switch_num_labels (swtch) < 2)
+    {
+      m_reason = "switch is a degenerate case";
+      return;
+    }
 
   collect (swtch);