[PATCH] Fix PR middle-end/80823, ICE: verify_flow_info failed

[Peter Bergner <bergner at vnet dot ibm dot com>]

The fix for PR80775 included a thinko bug that caused us to skip some
case label statements.  This leads to problems for test cases where we
have multiple case labels that point to the same unreachable block, but
are not mergeable since they don't have consecutive case values.
This leads to a problem, because we remove the unreachable block when
handling this first case label, but then we have a dangling reference
to that block with the skipped case label.  The fix is to remove the
unwanted increment, so that we handle the next case label and end up
removing it too.

This passed bootstrap and regtesting on powerpc64le-linux with no
regressions.  Is this ok for trunk?

Peter

gcc/
	PR middle-end/80823
	* tree-cfg.c (group_case_labels_stmt): Delete increment of "i";

gcc/testsuite/
	PR middle-end/80823
	* gcc.dg/pr80823.c: New test.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c	(revision 248375)
+++ gcc/tree-cfg.c	(working copy)
@@ -1726,7 +1726,6 @@ group_case_labels_stmt (gswitch *stmt)
 	    remove_edge_and_dominated_blocks (base_edge);
 	  gimple_switch_set_label (stmt, base_index, NULL_TREE);
 	  new_size--;
-	  i++;
 	}
     }
 
Index: gcc/testsuite/gcc.dg/pr80823.c
===================================================================
--- gcc/testsuite/gcc.dg/pr80823.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/pr80823.c	(working copy)
@@ -0,0 +1,23 @@
+/* PR middle-end/80823 ICE: verify_flow_info failed  */
+/* { dg-do compile }  */
+/* { dg-options "-O3" }  */
+
+int a, c;
+int b[1];
+static inline int
+fn1() {
+  switch (a)
+  case 0:
+  case 2:
+    return 1;
+  return 0;
+}
+void fn2() {
+  int i;
+  for (;; ++i) {
+    c = b[i];
+    int d = !fn1();
+    if (d)
+      __asm__("");
+  }
+}