PHIOPT: Factor out some code from match_simplify_replacement

This factors out the code checking if we have an empty bb
or one statement that feeds into the phi so it can be used
when adding diamond shaped bb form to match_simplify_replacement
in the next patch. Also allows for some improvements
in the next patches too.

OK? Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (empty_bb_or_one_feeding_into_p):
	New function.
	(match_simplify_replacement): Call
	empty_bb_or_one_feeding_into_p instead of doing it inline.

1 files changed, 62 insertions, 44 deletions

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index ce3409b..f3164b8 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -938,6 +938,66 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
   return NULL;
 }
 
+/* empty_bb_or_one_feeding_into_p returns true if bb was empty basic block
+   or it has one cheap preparation statement that feeds into the PHI
+   statement and it sets STMT to that statement. */
+static bool
+empty_bb_or_one_feeding_into_p (basic_block bb,
+				gimple *phi,
+				gimple *&stmt)
+{
+  stmt = nullptr;
+  gimple *stmt_to_move = nullptr;
+
+  if (empty_block_p (bb))
+    return true;
+
+  if (!single_pred_p (bb))
+    return false;
+
+  /* The middle bb cannot have phi nodes as we don't
+     move those assignments yet. */
+  if (!gimple_seq_empty_p (phi_nodes (bb)))
+    return false;
+
+  stmt_to_move = last_and_only_stmt (bb);
+  if (!stmt_to_move)
+    return false;
+
+  if (gimple_vuse (stmt_to_move))
+    return false;
+
+  if (gimple_could_trap_p (stmt_to_move)
+      || gimple_has_side_effects (stmt_to_move))
+    return false;
+
+  if (gimple_uses_undefined_value_p (stmt_to_move))
+    return false;
+
+  /* Allow assignments and not no calls.
+     As const calls don't match any of the above, yet they could
+     still have some side-effects - they could contain
+     gimple_could_trap_p statements, like floating point
+     exceptions or integer division by zero.  See PR70586.
+     FIXME: perhaps gimple_has_side_effects or gimple_could_trap_p
+     should handle this.  */
+  if (!is_gimple_assign (stmt_to_move))
+    return false;
+
+  tree lhs = gimple_assign_lhs (stmt_to_move);
+  gimple *use_stmt;
+  use_operand_p use_p;
+
+  /* Allow only a statement which feeds into the other stmt.  */
+  if (!lhs || TREE_CODE (lhs) != SSA_NAME
+      || !single_imm_use (lhs, &use_p, &use_stmt)
+      || use_stmt != phi)
+    return false;
+
+  stmt = stmt_to_move;
+  return true;
+}
+
 /*  The function match_simplify_replacement does the main work of doing the
     replacement using match and simplify.  Return true if the replacement is done.
     Otherwise return false.
@@ -963,50 +1023,8 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
 
   /* If the basic block only has a cheap preparation statement,
      allow it and move it once the transformation is done. */
-  if (!empty_block_p (middle_bb))
-    {
-      if (!single_pred_p (middle_bb))
-	return false;
-
-      /* The middle bb cannot have phi nodes as we don't
-	 move those assignments yet. */
-      if (!gimple_seq_empty_p (phi_nodes (middle_bb)))
-	return false;
-
-      stmt_to_move = last_and_only_stmt (middle_bb);
-      if (!stmt_to_move)
-	return false;
-
-      if (gimple_vuse (stmt_to_move))
-	return false;
-
-      if (gimple_could_trap_p (stmt_to_move)
-	  || gimple_has_side_effects (stmt_to_move))
-	return false;
-
-      if (gimple_uses_undefined_value_p (stmt_to_move))
-	return false;
-
-      /* Allow assignments and not no calls.
-	 As const calls don't match any of the above, yet they could
-	 still have some side-effects - they could contain
-	 gimple_could_trap_p statements, like floating point
-	 exceptions or integer division by zero.  See PR70586.
-	 FIXME: perhaps gimple_has_side_effects or gimple_could_trap_p
-	 should handle this.  */
-      if (!is_gimple_assign (stmt_to_move))
-	return false;
-
-      tree lhs = gimple_assign_lhs (stmt_to_move);
-      gimple *use_stmt;
-      use_operand_p use_p;
-
-      /* Allow only a statement which feeds into the phi.  */
-      if (!lhs || TREE_CODE (lhs) != SSA_NAME
-	  || !single_imm_use (lhs, &use_p, &use_stmt)
-	  || use_stmt != phi)
-	return false;
-    }
+  if (!empty_bb_or_one_feeding_into_p (middle_bb, phi, stmt_to_move))
+    return false;
 
     /* At this point we know we have a GIMPLE_COND with two successors.
      One successor is BB, the other successor is an empty block which