tree-optimization/98845 - ICE with tail-merging and DCE/DSE disabled

The following shows that tail-merging will make dead SSA defs live
in paths where it wasn't before, possibly introducing UB or as
in this case, uses of abnormals that eventually fail coalescing
later.  The fix is to register such defs for stmt comparison.

	PR tree-optimization/98845
	* tree-ssa-tail-merge.cc (stmt_local_def): Consider a
	def with no uses not local.

	* gcc.dg/pr98845.c: New testcase.
	* gcc.dg/pr81192.c: Adjust.

(cherry picked from commit 6b8a8c9fd68c5dabaec5ddbc25efeade44f37a14)

gcc/testsuite/gcc.dg/pr81192.c

@@ -25,12 +25,16 @@ void __GIMPLE(ssa, startwith("pre")) fn2   ()
   if (j_6(D) != _Literal (int)2147483647)
     goto __BB4;
   else
-    goto __BB5;
+    goto __BB9;
 
   __BB(4):
   iftmp2_8 = j_6(D) + _Literal (int)1;
   goto __BB5;
 
+  __BB(9):
+  iftmp2_8 = j_6(D) + _Literal (int)1;
+  goto __BB5;
+
   __BB(5):
   b_lsm6_10 = _Literal (int)2147483647;
   goto __BB6;

gcc/testsuite/gcc.dg/pr98845.c

@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-dce -fno-tree-dse" } */
+
+int n;
+
+__attribute__ ((returns_twice)) void
+foo (void);
+
+void
+bar (void);
+
+void
+quux (int x)
+{
+  if (x)
+    ++x;
+  else
+    {
+      if (n)
+        {
+          x = 1;
+          foo ();
+        }
+      else
+        bar ();
+
+      if (n)
+        {
+          ++x;
+          ++n;
+        }
+    }
+}

gcc/tree-ssa-tail-merge.cc

@@ -336,10 +336,13 @@ stmt_local_def (gimple *stmt)
 
   def_bb = gimple_bb (stmt);
 
+  bool any_use = false;
   FOR_EACH_IMM_USE_FAST (use_p, iter, val)
     {
       if (is_gimple_debug (USE_STMT (use_p)))
 	continue;
+
+      any_use = true;
       bb = gimple_bb (USE_STMT (use_p));
       if (bb == def_bb)
 	continue;
@@ -351,6 +354,11 @@ stmt_local_def (gimple *stmt)
       return false;
     }
 
+  /* When there is no use avoid making the stmt live on other paths.
+     This can happen with DCE disabled or not done as seen in PR98845.  */
+  if (!any_use)
+    return false;
+
   return true;
 }