Make early return predictor more precise.

2017-06-21  Martin Liska  <mliska@suse.cz>

	PR tree-optimization/79489
	* gimplify.c (maybe_add_early_return_predict_stmt): New
	function.
	(gimplify_return_expr): Call the function.
	* predict.c (tree_estimate_probability_bb): Remove handling
	of early return.
	* predict.def: Update comment about early return predictor.
	* gimple-predict.h (is_gimple_predict): New function.
	* predict.def: Change default value of early return to 66.
	* tree-tailcall.c (find_tail_calls): Skip GIMPLE_PREDICT
	statements.
	* passes.def: Put pass_strip_predict_hints to the beginning of
	IPA passes.

From-SVN: r249450

gcc/ChangeLog

+2017-06-21  Martin Liska  <mliska@suse.cz>
+
+	PR tree-optimization/79489
+	* gimplify.c (maybe_add_early_return_predict_stmt): New
+	function.
+	(gimplify_return_expr): Call the function.
+	* predict.c (tree_estimate_probability_bb): Remove handling
+	of early return.
+	* predict.def: Update comment about early return predictor.
+	* gimple-predict.h (is_gimple_predict): New function.
+	* predict.def: Change default value of early return to 66.
+	* tree-tailcall.c (find_tail_calls): Skip GIMPLE_PREDICT
+	statements.
+	* passes.def: Put pass_strip_predict_hints to the beginning of
+	IPA passes.
+
 2017-06-21  Pierre-Marie de Rodat  <derodat@adacore.com>
 
 	* dwarf2out.c (gen_decl_die): Remove the guard to skip file-scope

gcc/gimple-low.c

@@ -30,6 +30,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "calls.h"
 #include "gimple-iterator.h"
 #include "gimple-low.h"
+#include "predict.h"
+#include "gimple-predict.h"
 
 /* The differences between High GIMPLE and Low GIMPLE are the
    following:

gcc/gimple-predict.h

@@ -80,4 +80,12 @@ gimple_build_predict (enum br_predictor predictor, enum prediction outcome)
   return p;
 }
 
+/* Return true if GS is a GIMPLE_PREDICT statement.  */
+
+static inline bool
+is_gimple_predict (const gimple *gs)
+{
+  return gimple_code (gs) == GIMPLE_PREDICT;
+}
+
 #endif  /* GCC_GIMPLE_PREDICT_H */

gcc/gimplify.c

@@ -1428,6 +1428,20 @@ gimplify_bind_expr (tree *expr_p, gimple_seq *pre_p)
   return GS_ALL_DONE;
 }
 
+/* Maybe add early return predict statement to PRE_P sequence.  */
+
+static void
+maybe_add_early_return_predict_stmt (gimple_seq *pre_p)
+{
+  /* If we are not in a conditional context, add PREDICT statement.  */
+  if (gimple_conditional_context ())
+    {
+      gimple *predict = gimple_build_predict (PRED_TREE_EARLY_RETURN,
+					      NOT_TAKEN);
+      gimplify_seq_add_stmt (pre_p, predict);
+    }
+}
+
 /* Gimplify a RETURN_EXPR.  If the expression to be returned is not a
    GIMPLE value, it is assigned to a new temporary and the statement is
    re-written to return the temporary.
@@ -1458,6 +1472,7 @@ gimplify_return_expr (tree stmt, gimple_seq *pre_p)
       || TREE_CODE (ret_expr) == RESULT_DECL
       || ret_expr == error_mark_node)
     {
+      maybe_add_early_return_predict_stmt (pre_p);
       greturn *ret = gimple_build_return (ret_expr);
       gimple_set_no_warning (ret, TREE_NO_WARNING (stmt));
       gimplify_seq_add_stmt (pre_p, ret);
@@ -1525,6 +1540,7 @@ gimplify_return_expr (tree stmt, gimple_seq *pre_p)
 
   gimplify_and_add (TREE_OPERAND (stmt, 0), pre_p);
 
+  maybe_add_early_return_predict_stmt (pre_p);
   ret = gimple_build_return (result);
   gimple_set_no_warning (ret, TREE_NO_WARNING (stmt));
   gimplify_seq_add_stmt (pre_p, ret);

gcc/passes.def

@@ -107,6 +107,7 @@ along with GCC; see the file COPYING3.  If not see
 	     early optimizations again.  It is thus good idea to do this
 	      late.  */
 	  NEXT_PASS (pass_split_functions);
+	  NEXT_PASS (pass_strip_predict_hints);
       POP_INSERT_PASSES ()
       NEXT_PASS (pass_release_ssa_names);
       NEXT_PASS (pass_rebuild_cgraph_edges);

gcc/predict.c

@@ -2739,7 +2739,6 @@ tree_estimate_probability_bb (basic_block bb, bool local_only)
 {
   edge e;
   edge_iterator ei;
-  gimple *last;
 
   FOR_EACH_EDGE (e, ei, bb->succs)
     {
@@ -2766,46 +2765,6 @@ tree_estimate_probability_bb (basic_block bb, bool local_only)
 	    }
 	}
 
-      /* Predict early returns to be probable, as we've already taken
-	 care for error returns and other cases are often used for
-	 fast paths through function.
-
-	 Since we've already removed the return statements, we are
-	 looking for CFG like:
-
-	 if (conditional)
-	 {
-	 ..
-	 goto return_block
-	 }
-	 some other blocks
-	 return_block:
-	 return_stmt.  */
-      if (e->dest != bb->next_bb
-	  && e->dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
-	  && single_succ_p (e->dest)
-	  && single_succ_edge (e->dest)->dest == EXIT_BLOCK_PTR_FOR_FN (cfun)
-	  && (last = last_stmt (e->dest)) != NULL
-	  && gimple_code (last) == GIMPLE_RETURN)
-	{
-	  edge e1;
-	  edge_iterator ei1;
-
-	  if (single_succ_p (bb))
-	    {
-	      FOR_EACH_EDGE (e1, ei1, bb->preds)
-		if (!predicted_by_p (e1->src, PRED_NULL_RETURN)
-		    && !predicted_by_p (e1->src, PRED_CONST_RETURN)
-		    && !predicted_by_p (e1->src, PRED_NEGATIVE_RETURN))
-		  predict_edge_def (e1, PRED_TREE_EARLY_RETURN, NOT_TAKEN);
-	    }
-	  else
-	    if (!predicted_by_p (e->src, PRED_NULL_RETURN)
-		&& !predicted_by_p (e->src, PRED_CONST_RETURN)
-		&& !predicted_by_p (e->src, PRED_NEGATIVE_RETURN))
-	      predict_edge_def (e, PRED_TREE_EARLY_RETURN, NOT_TAKEN);
-	}
-
       /* Look for block we are guarding (ie we dominate it,
 	 but it doesn't postdominate us).  */
       if (e->dest != EXIT_BLOCK_PTR_FOR_FN (cfun) && e->dest != bb

gcc/predict.def

@@ -128,18 +128,9 @@ DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", HITRATE (59), 0)
    indefinitely.  */
 DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", HITRATE (75), 0)
 
-/* Branch causing function to terminate is probably not taken. 
-   FIXME: early return currently predicts code:
-   int foo (int a)
-   {
-      if (a)
-	bar();
-      else
-	bar2();
-   }
-   even though there is no return statement involved.  We probably want to track
-   this from FE or retire the predictor.  */
-DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (54), 0)
+/* Branch causing function to terminate is probably not taken.  */
+DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66),
+	       0)
 
 /* Branch containing goto is probably not taken.
    FIXME: Currently not used.  */

gcc/tree-tailcall.c

@@ -421,6 +421,7 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
       if (gimple_code (stmt) == GIMPLE_LABEL
 	  || gimple_code (stmt) == GIMPLE_RETURN
 	  || gimple_code (stmt) == GIMPLE_NOP
+	  || gimple_code (stmt) == GIMPLE_PREDICT
 	  || gimple_clobber_p (stmt)
 	  || is_gimple_debug (stmt))
 	continue;
@@ -555,6 +556,7 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
 
       if (gimple_code (stmt) == GIMPLE_LABEL
 	  || gimple_code (stmt) == GIMPLE_NOP
+	  || gimple_code (stmt) == GIMPLE_PREDICT
 	  || gimple_clobber_p (stmt)
 	  || is_gimple_debug (stmt))
 	continue;