Early builtin_unreachable removal must examine dependencies.

Even if all uses of a name are dominated by the unreachable branch,
recomputation of a value in the defintion of a name might be reachable.

	PR tree-optimization/123300
	gcc/
	* gimple-range-gori.cc (gori_map::exports_and_deps): New.
	* gimple-range-gori.h (exports_and_deps): New prototype.
	(FOR_EACH_GORI_EXPORT_AND_DEP_NAME): New macro.
	* tree-vrp.cc (remove_unreachable:remove_unreachable): Initialize
	m_tmp bitmap.
	(remove_unreachable:~remove_unreachable): Dispose of m_tmp bitmap.
	(remove_unreachable:fully_replaceable): Move from static function
	and check reachability of exports and dependencies.

	gcc/testsuite/
	* gcc.dg/pr123300.c: New.

gcc/gimple-range-gori.cc

@@ -383,6 +383,28 @@ gori_map::exports (basic_block bb)
   return m_outgoing[bb->index];
 }
 
+// Return the bitmap vector of all exports AND their dependencies from BB
+// in TMPBIT.  Calculate if necessary.  Return TMPBIT.
+
+bitmap
+gori_map::exports_and_deps (basic_block bb, bitmap tmpbit)
+{
+  if (bb->index >= (signed int)m_outgoing.length () || !m_outgoing[bb->index])
+    calculate_gori (bb);
+  bitmap_copy (tmpbit, m_outgoing[bb->index]);
+  if (!bitmap_empty_p (tmpbit))
+    {
+      tree name;
+      FOR_EACH_GORI_EXPORT_NAME (this, bb, name)
+	{
+	  bitmap dep = get_def_chain (name);
+	  if (dep)
+	    bitmap_ior_into (tmpbit, dep);
+	}
+    }
+  return tmpbit;
+}
+
 // Return the bitmap vector of all imports to BB.  Calculate if necessary.
 
 bitmap

gcc/gimple-range-gori.h

@@ -99,6 +99,7 @@ public:
   bool is_export_p (tree name, basic_block bb = NULL);
   bool is_import_p (tree name, basic_block bb);
   bitmap exports (basic_block bb);
+  bitmap exports_and_deps (basic_block bb, bitmap tmpbit);
   bitmap imports (basic_block bb);
   void set_range_invariant (tree name, bool invariant = true);
 
@@ -223,7 +224,7 @@ bool gori_on_edge (class ssa_cache &r, edge e, range_query *query = NULL);
 bool gori_name_on_edge (vrange &r, tree name, edge e, range_query *q = NULL);
 
 // For each name that is an import into BB's exports..
-#define FOR_EACH_GORI_IMPORT_NAME(gorimap, bb, name)			\
+#define FOR_EACH_GORI_IMPORT_NAME(gorimap, bb, name)		\
   for (gori_export_iterator iter ((gorimap)->imports ((bb)));	\
        ((name) = iter.get_name ());				\
        iter.next ())
@@ -234,6 +235,12 @@ bool gori_name_on_edge (vrange &r, tree name, edge e, range_query *q = NULL);
        ((name) = iter.get_name ());				\
        iter.next ())
 
+// For each name and all their dependencies possibly exported from block BB.
+#define FOR_EACH_GORI_EXPORT_AND_DEP_NAME(gorimap, bb, name, bm)	   \
+  for (gori_export_iterator iter ((gorimap)->exports_and_deps ((bb),(bm))); \
+       ((name) = iter.get_name ());					   \
+       iter.next ())
+
 // Used to assist with iterating over the GORI export list in various ways
 class gori_export_iterator {
 public:

gcc/testsuite/gcc.dg/pr123300.c

@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+[[gnu::noipa]] void
+bar (int a, int b)
+{
+  if (a < 0)
+    __builtin_abort ();
+}
+
+[[gnu::noipa]] void
+foo (int n, bool p)
+{
+  for (int i = n; i-- > 0;)
+    {
+      const int x = 1 << i;
+      if (x <= 0)
+	__builtin_unreachable ();
+      if (p)
+	bar (i, x);
+    }
+}
+
+int
+main ()
+{
+  foo (4, true);
+}
+/* { dg-final { scan-tree-dump "__builtin_unreachable" "vrp1" } } */
+

gcc/tree-vrp.cc

@@ -87,15 +87,17 @@ along with GCC; see the file COPYING3.  If not see
 class remove_unreachable {
 public:
   remove_unreachable (range_query &r, bool all) : m_ranger (r), final_p (all)
-    { m_list.create (30); }
-  ~remove_unreachable () { m_list.release (); }
+    { m_list.create (30); m_tmp = BITMAP_ALLOC (NULL); }
+  ~remove_unreachable () { BITMAP_FREE (m_tmp); m_list.release (); }
   void handle_early (gimple *s, edge e);
   void maybe_register (gimple *s);
   bool remove ();
   bool remove_and_update_globals ();
+  bool fully_replaceable (tree name, basic_block bb);
   vec<std::pair<int, int> > m_list;
   range_query &m_ranger;
   bool final_p;
+  bitmap m_tmp;
 };
 
 // Check if block BB has a __builtin_unreachable () call on one arm, and
@@ -141,8 +143,8 @@ remove_unreachable::maybe_register (gimple *s)
 //    goto <bb 3>; [0.00%]
 //  Any additional use of _1 or _2 in this block invalidates early replacement.
 
-static bool
-fully_replaceable (tree name, basic_block bb)
+bool
+remove_unreachable::fully_replaceable (tree name, basic_block bb)
 {
   use_operand_p use_p;
   imm_use_iterator iter;
@@ -213,9 +215,11 @@ remove_unreachable::handle_early (gimple *s, edge e)
   gcc_checking_assert (gimple_outgoing_range_stmt_p (e->src) == s);
   gcc_checking_assert (!final_p);
 
-  // Check if every export use is dominated by this branch.
+  // Check if every export and its dependencies are dominated by this branch.
+  // Dependencies are required as it needs to dominate potential
+  // recalculations.  See PR 123300.
   tree name;
-  FOR_EACH_GORI_EXPORT_NAME (m_ranger.gori_ssa (), e->src, name)
+  FOR_EACH_GORI_EXPORT_AND_DEP_NAME (m_ranger.gori_ssa (), e->src, name, m_tmp)
     {
       if (!fully_replaceable (name, e->src))
 	return;