Support __builtin_expect_with_probability for analysis of # of loop iterations.

2019-07-04  Martin Liska  <mliska@suse.cz>

	* tree-ssa-loop-niter.c (get_upper_bound_based_on_builtin_expr_with_prob):
	New function.
	(estimate_numbers_of_iterations):
	Support __builtin_expect_with_probability for analysis
	of # of loop iterations.

From-SVN: r273087

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 41b8b14..d4e9991 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,11 @@
+2019-07-04  Martin Liska  <mliska@suse.cz>
+
+       * tree-ssa-loop-niter.c (get_upper_bound_based_on_builtin_expr_with_prob):
+       New function.
+       (estimate_numbers_of_iterations):
+       Support __builtin_expect_with_probability for analysis
+       of # of loop iterations.
+
 2019-07-04  Alexandre Oliva <oliva@adacore.com>
 
        * doc/generic.texi (Cleanups): Document EH_ELSE_EXPR.

diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index f513859..5e75a41 100644 (file)
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -4183,6 +4183,55 @@ maybe_lower_iteration_bound (struct loop *loop)
   delete not_executed_last_iteration;
 }
 
+/* Get expected upper bound for number of loop iterations for
+   BUILT_IN_EXPECT_WITH_PROBABILITY for a condition COND.  */
+
+static tree
+get_upper_bound_based_on_builtin_expr_with_prob (gcond *cond)
+{
+  if (cond == NULL)
+    return NULL_TREE;
+
+  tree lhs = gimple_cond_lhs (cond);
+  if (TREE_CODE (lhs) != SSA_NAME)
+    return NULL_TREE;
+
+  gimple *stmt = SSA_NAME_DEF_STMT (gimple_cond_lhs (cond));
+  gcall *def = dyn_cast<gcall *> (stmt);
+  if (def == NULL)
+    return NULL_TREE;
+
+  tree decl = gimple_call_fndecl (def);
+  if (!decl
+      || !fndecl_built_in_p (decl, BUILT_IN_EXPECT_WITH_PROBABILITY)
+      || gimple_call_num_args (stmt) != 3)
+    return NULL_TREE;
+
+  tree c = gimple_call_arg (def, 1);
+  tree condt = TREE_TYPE (lhs);
+  tree res = fold_build2 (gimple_cond_code (cond),
+                         condt, c,
+                         gimple_cond_rhs (cond));
+  if (TREE_CODE (res) != INTEGER_CST)
+    return NULL_TREE;
+
+
+  tree prob = gimple_call_arg (def, 2);
+  tree t = TREE_TYPE (prob);
+  tree one
+    = build_real_from_int_cst (t,
+                              integer_one_node);
+  if (integer_zerop (res))
+    prob = fold_build2 (MINUS_EXPR, t, one, prob);
+  tree r = fold_build2 (RDIV_EXPR, t, one, prob);
+  if (TREE_CODE (r) != REAL_CST)
+    return NULL_TREE;
+
+  HOST_WIDE_INT probi
+    = real_to_integer (TREE_REAL_CST_PTR (r));
+  return build_int_cst (condt, probi);
+}
+
 /* Records estimates on numbers of iterations of LOOP.  If USE_UNDEFINED_P
    is true also use estimates derived from undefined behavior.  */
 
@@ -4231,6 +4280,23 @@ estimate_numbers_of_iterations (struct loop *loop)
   likely_exit = single_likely_exit (loop);
   FOR_EACH_VEC_ELT (exits, i, ex)
     {
+      if (ex == likely_exit)
+       {
+         gimple *stmt = last_stmt (ex->src);
+         if (stmt != NULL)
+           {
+             gcond *cond = dyn_cast<gcond *> (stmt);
+             tree niter_bound
+               = get_upper_bound_based_on_builtin_expr_with_prob (cond);
+             if (niter_bound != NULL_TREE)
+               {
+                 widest_int max = derive_constant_upper_bound (niter_bound);
+                 record_estimate (loop, niter_bound, max, cond,
+                                  true, true, false);
+               }
+           }
+       }
+
       if (!number_of_iterations_exit (loop, ex, &niter_desc, false, false))
        continue;