Special handle for mul/div minus one when kAllUsesTruncatingToInt32

BUG=
R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/24521002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16943 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.cc

@@ -1237,6 +1237,16 @@ HValue* HMul::Canonicalize() {
 }
 
 
+bool HMul::MulMinusOne() {
+  if (left()->EqualsInteger32Constant(-1) ||
+      right()->EqualsInteger32Constant(-1)) {
+    return true;
+  }
+
+  return false;
+}
+
+
 HValue* HMod::Canonicalize() {
   return this;
 }
@@ -1622,10 +1632,13 @@ Range* HMul::InferRange(Zone* zone) {
     Range* a = left()->range();
     Range* b = right()->range();
     Range* res = a->Copy(zone);
-    if (!res->MulAndCheckOverflow(r, b)) {
-      // Clearing the kCanOverflow flag when kAllUsesAreTruncatingToInt32
-      // would be wrong, because truncated integer multiplication is too
-      // precise and therefore not the same as converting to Double and back.
+    if (!res->MulAndCheckOverflow(r, b) ||
+        (((r.IsInteger32() && CheckFlag(kAllUsesTruncatingToInt32)) ||
+         (r.IsSmi() && CheckFlag(kAllUsesTruncatingToSmi))) &&
+         MulMinusOne())) {
+      // Truncated int multiplication is too precise and therefore not the
+      // same as converting to Double and back.
+      // Handle truncated integer multiplication by -1 special.
       ClearFlag(kCanOverflow);
     }
     res->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToSmi) &&
@@ -1647,7 +1660,10 @@ Range* HDiv::InferRange(Zone* zone) {
     result->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
                                   (a->CanBeMinusZero() ||
                                    (a->CanBeZero() && b->CanBeNegative())));
-    if (!a->Includes(kMinInt) || !b->Includes(-1)) {
+    if (!a->Includes(kMinInt) ||
+        !b->Includes(-1) ||
+        CheckFlag(kAllUsesTruncatingToInt32)) {
+      // It is safe to clear kCanOverflow when kAllUsesTruncatingToInt32.
       ClearFlag(HValue::kCanOverflow);
     }
 
@@ -2596,6 +2612,12 @@ void HBinaryOperation::InferRepresentation(HInferRepresentationPhase* h_infer) {
   ASSERT(CheckFlag(kFlexibleRepresentation));
   Representation new_rep = RepresentationFromInputs();
   UpdateRepresentation(new_rep, h_infer, "inputs");
+
+  if (representation().IsSmi() && HasNonSmiUse()) {
+    UpdateRepresentation(
+        Representation::Integer32(), h_infer, "use requirements");
+  }
+
   if (observed_output_representation_.IsNone()) {
     new_rep = RepresentationFromUses();
     UpdateRepresentation(new_rep, h_infer, "uses");
@@ -2603,11 +2625,6 @@ void HBinaryOperation::InferRepresentation(HInferRepresentationPhase* h_infer) {
     new_rep = RepresentationFromOutput();
     UpdateRepresentation(new_rep, h_infer, "output");
   }
-
-  if (representation().IsSmi() && HasNonSmiUse()) {
-    UpdateRepresentation(
-        Representation::Integer32(), h_infer, "use requirements");
-  }
 }
 
 
@@ -2634,7 +2651,7 @@ bool HBinaryOperation::IgnoreObservedOutputRepresentation(
   return ((current_rep.IsInteger32() && CheckUsesForFlag(kTruncatingToInt32)) ||
           (current_rep.IsSmi() && CheckUsesForFlag(kTruncatingToSmi))) &&
          // Mul in Integer32 mode would be too precise.
-         !this->IsMul();
+         (!this->IsMul() || HMul::cast(this)->MulMinusOne());
 }
 
 

src/hydrogen-instructions.h

@@ -4581,6 +4581,8 @@ class HMul V8_FINAL : public HArithmeticBinaryOperation {
     HArithmeticBinaryOperation::UpdateRepresentation(new_rep, h_infer, reason);
   }
 
+  bool MulMinusOne();
+
   DECLARE_CONCRETE_INSTRUCTION(Mul)
 
  protected:

test/mjsunit/div-mul-minus-one.js

@@ -0,0 +1,53 @@
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax
+
+function div(g) {
+  return (g/-1) ^ 1
+}
+
+var kMinInt = 1 << 31;
+var expected_MinInt = div(kMinInt);
+var expected_minus_zero = div(0);
+%OptimizeFunctionOnNextCall(div);
+assertEquals(expected_MinInt, div(kMinInt));
+assertOptimized(div);
+assertEquals(expected_minus_zero , div(0));
+assertOptimized(div);
+
+function mul(g) {
+  return (g * -1) ^ 1
+}
+
+expected_MinInt = mul(kMinInt);
+expected_minus_zero = mul(0);
+%OptimizeFunctionOnNextCall(mul);
+assertEquals(expected_MinInt, mul(kMinInt));
+assertOptimized(mul);
+assertEquals(expected_minus_zero , mul(0));
+assertOptimized(mul);