From 458dc58b59125a99b2020635bcc5452e486a190a Mon Sep 17 00:00:00 2001
From: Robert Fancsik <frobert@inf.u-szeged.hu>
Date: Mon, 27 Nov 2017 12:56:50 +0100
Subject: [PATCH] Improve multiplication in vm

This patch improves the ecma_integers_values multiplication by checking if the multiplier or multiplicand is power of 2.
If it is it uses right shift instead of multiplication.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu
---
 jerry-core/ecma/base/ecma-helpers-number.c | 25 ++++++++++++++++++++++
 jerry-core/ecma/base/ecma-helpers.h        |  1 +
 jerry-core/vm/vm.c                         |  2 +-
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/jerry-core/ecma/base/ecma-helpers-number.c b/jerry-core/ecma/base/ecma-helpers-number.c
index 19db451e3..ea43c5071 100644
--- a/jerry-core/ecma/base/ecma-helpers-number.c
+++ b/jerry-core/ecma/base/ecma-helpers-number.c
@@ -653,6 +653,31 @@ ecma_number_calc_remainder (ecma_number_t left_num, /**< left operand */
   return r;
 } /* ecma_number_calc_remainder */
 
+/**
+ * ECMA-integer number multiplication.
+ *
+ * @return number - result of multiplication.
+ */
+inline ecma_value_t __attr_always_inline___
+ecma_integer_multiply (ecma_integer_value_t left_integer, /**< left operand */
+                       ecma_integer_value_t right_integer) /**< right operand */
+{
+#if defined (__GNUC__) || defined (__clang__)
+  /* Check if left_integer is power of 2 */
+  if (unlikely ((left_integer & (left_integer - 1)) == 0))
+  {
+    /* Right shift right_integer with log2 (left_integer) */
+    return ecma_make_integer_value (right_integer << (__builtin_ctz ((unsigned int) left_integer)));
+  }
+  else if (unlikely ((right_integer & (right_integer - 1)) == 0))
+  {
+    /* Right shift left_integer with log2 (right_integer) */
+    return ecma_make_integer_value (left_integer << (__builtin_ctz ((unsigned int) right_integer)));
+  }
+#endif /* defined (__GNUC__) || defined (__clang__) */
+  return ecma_make_integer_value (left_integer * right_integer);
+} /* ecma_integer_multiply */
+
 /**
  * @}
  * @}
diff --git a/jerry-core/ecma/base/ecma-helpers.h b/jerry-core/ecma/base/ecma-helpers.h
index a1783849c..520b3d1e7 100644
--- a/jerry-core/ecma/base/ecma-helpers.h
+++ b/jerry-core/ecma/base/ecma-helpers.h
@@ -243,6 +243,7 @@ ecma_number_t ecma_number_get_prev (ecma_number_t num);
 ecma_number_t ecma_number_get_next (ecma_number_t num);
 ecma_number_t ecma_number_trunc (ecma_number_t num);
 ecma_number_t ecma_number_calc_remainder (ecma_number_t left_num, ecma_number_t right_num);
+ecma_value_t ecma_integer_multiply (ecma_integer_value_t left_integer, ecma_integer_value_t right_integer);
 lit_utf8_size_t ecma_number_to_decimal (ecma_number_t num, lit_utf8_byte_t *out_digits_p, int32_t *out_decimal_exp_p);
 lit_utf8_size_t ecma_number_to_binary_floating_point_number (ecma_number_t num,
                                                              lit_utf8_byte_t *out_digits_p,
diff --git a/jerry-core/vm/vm.c b/jerry-core/vm/vm.c
index d1cac7bef..3dd634615 100644
--- a/jerry-core/vm/vm.c
+++ b/jerry-core/vm/vm.c
@@ -1793,7 +1793,7 @@ vm_loop (vm_frame_ctx_t *frame_ctx_p) /**< frame context */
                 && left_value != 0
                 && right_value != 0)
             {
-              result = ecma_make_integer_value (left_integer * right_integer);
+              result = ecma_integer_multiply (left_integer, right_integer);
               break;
             }