predict.c (predict_loops): Predict for short-circuit conditions.

gcc:
	2012-10-08  Dehao Chen  <dehao@google.com>

	* predict.c (predict_loops): Predict for short-circuit conditions.
	(predict_extra_loop_exits): New Function.

testsuite:
	2012-10-08  Dehao Chen  <dehao@google.com>

	* g++.dg/predict-loop-exit-1.C: New.
	* g++.dg/predict-loop-exit-2.C: New.
	* g++.dg/predict-loop-exit-3.C: New.

From-SVN: r192215

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 39e23bd..14bdc37 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2012-10-08  Dehao Chen  <dehao@google.com>
+
+       * predict.c (predict_loops): Predict for short-circuit conditions.
+       (predict_extra_loop_exits): New Function.
+
 2012-10-08  Steven Bosscher  <steven@gcc.gnu.org>
 
        * bitmap.h (bitmap_and_into): Update prototype.

diff --git a/gcc/predict.c b/gcc/predict.c
index f0db9f4..4917399 100644 (file)
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -1296,7 +1296,87 @@ predict_iv_comparison (struct loop *loop, basic_block bb,
        predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE_GUESS, NOT_TAKEN);
     }
 }
- 
+
+/* Predict for extra loop exits that will lead to EXIT_EDGE. The extra loop
+   exits are resulted from short-circuit conditions that will generate an
+   if_tmp. E.g.:
+
+   if (foo() || global > 10)
+     break;
+
+   This will be translated into:
+
+   BB3:
+     loop header...
+   BB4:
+     if foo() goto BB6 else goto BB5
+   BB5:
+     if global > 10 goto BB6 else goto BB7
+   BB6:
+     goto BB7
+   BB7:
+     iftmp = (PHI 0(BB5), 1(BB6))
+     if iftmp == 1 goto BB8 else goto BB3
+   BB8:
+     outside of the loop...
+
+   The edge BB7->BB8 is loop exit because BB8 is outside of the loop.
+   From the dataflow, we can infer that BB4->BB6 and BB5->BB6 are also loop
+   exits. This function takes BB7->BB8 as input, and finds out the extra loop
+   exits to predict them using PRED_LOOP_EXIT.  */
+
+static void
+predict_extra_loop_exits (edge exit_edge)
+{
+  unsigned i;
+  bool check_value_one;
+  gimple phi_stmt;
+  tree cmp_rhs, cmp_lhs;
+  gimple cmp_stmt = last_stmt (exit_edge->src);
+
+  if (!cmp_stmt || gimple_code (cmp_stmt) != GIMPLE_COND)
+    return;
+  cmp_rhs = gimple_cond_rhs (cmp_stmt);
+  cmp_lhs = gimple_cond_lhs (cmp_stmt);
+  if (!TREE_CONSTANT (cmp_rhs)
+      || !(integer_zerop (cmp_rhs) || integer_onep (cmp_rhs)))
+    return;
+  if (TREE_CODE (cmp_lhs) != SSA_NAME)
+    return;
+
+  /* If check_value_one is true, only the phi_args with value '1' will lead
+     to loop exit. Otherwise, only the phi_args with value '0' will lead to
+     loop exit.  */
+  check_value_one = (((integer_onep (cmp_rhs))
+                   ^ (gimple_cond_code (cmp_stmt) == EQ_EXPR))
+                   ^ ((exit_edge->flags & EDGE_TRUE_VALUE) != 0));
+
+  phi_stmt = SSA_NAME_DEF_STMT (cmp_lhs);
+  if (!phi_stmt || gimple_code (phi_stmt) != GIMPLE_PHI)
+    return;
+
+  for (i = 0; i < gimple_phi_num_args (phi_stmt); i++)
+    {
+      edge e1;
+      edge_iterator ei;
+      tree val = gimple_phi_arg_def (phi_stmt, i);
+      edge e = gimple_phi_arg_edge (phi_stmt, i);
+
+      if (!TREE_CONSTANT (val) || !(integer_zerop (val) || integer_onep (val)))
+       continue;
+      if ((check_value_one ^ integer_onep (val)) == 1)
+       continue;
+      if (EDGE_COUNT (e->src->succs) != 1)
+       {
+         predict_paths_leading_to_edge (e, PRED_LOOP_EXIT, NOT_TAKEN);
+         continue;
+       }
+
+      FOR_EACH_EDGE (e1, ei, e->src->preds)
+       predict_paths_leading_to_edge (e1, PRED_LOOP_EXIT, NOT_TAKEN);
+    }
+}
+
 /* Predict edge probabilities by exploiting loop structure.  */
 
 static void
@@ -1332,6 +1412,8 @@ predict_loops (void)
          int probability;
          enum br_predictor predictor;
 
+         predict_extra_loop_exits (ex);
+
          if (number_of_iterations_exit (loop, ex, &niter_desc, false))
            niter = niter_desc.niter;
          if (!niter || TREE_CODE (niter_desc.niter) != INTEGER_CST)

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9b0c0ba..1345f72 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2012-10-08  Dehao Chen  <dehao@google.com>
+
+       * g++.dg/predict-loop-exit-1.C: New.
+       * g++.dg/predict-loop-exit-2.C: New.
+       * g++.dg/predict-loop-exit-3.C: New.
+
 2012-10-08  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
        * gcc.target/i386/pr54445-1.c: Require tls_runtime, add tls options.

diff --git a/gcc/testsuite/g++.dg/predict-loop-exit-1.C b/gcc/testsuite/g++.dg/predict-loop-exit-1.C
new file mode 100644 (file)
index 0000000..2289552
--- /dev/null
+++ b/gcc/testsuite/g++.dg/predict-loop-exit-1.C
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
+
+int g;
+int foo();
+void test() {
+  while (foo() && g < 10)
+    g++;
+  return;
+}
+
+/* { dg-final { scan-tree-dump-times "loop exit heuristics:" 3 "profile_estimate"} } */
+/* { dg-final { cleanup-tree-dump "profile_estimate" } } */

diff --git a/gcc/testsuite/g++.dg/predict-loop-exit-2.C b/gcc/testsuite/g++.dg/predict-loop-exit-2.C
new file mode 100644 (file)
index 0000000..1a5880b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/predict-loop-exit-2.C
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
+
+int g;
+int foo();
+void test() {
+  while (foo() || g < 10)
+    g++;
+  return;
+}
+
+/* { dg-final { scan-tree-dump-times "loop exit heuristics:" 2 "profile_estimate"} } */
+/* { dg-final { cleanup-tree-dump "profile_estimate" } } */

diff --git a/gcc/testsuite/g++.dg/predict-loop-exit-3.C b/gcc/testsuite/g++.dg/predict-loop-exit-3.C
new file mode 100644 (file)
index 0000000..9afc78e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/predict-loop-exit-3.C
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
+
+int g;
+int foo();
+void test() {
+  while (foo() && (g < 10 || g > 20))
+    g++;
+  return;
+}
+
+/* { dg-final { scan-tree-dump-times "loop exit heuristics:" 3 "profile_estimate"} } */
+/* { dg-final { cleanup-tree-dump "profile_estimate" } } */