Optimize ~~(expr) in optimized code.

~~ is commonly used to truncate a value to int32 (ToInt32).

This change avoid actually emitting the bitwise operations, and
just truncates the subexpression of ~~.

BUG=v8:2037
TEST=test/mjsunit/compiler/optimize-bitnot.js
Review URL: https://chromiumcodereview.appspot.com/10123007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11390 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -1295,6 +1295,7 @@ LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
 LInstruction* LChunkBuilder::DoBitNot(HBitNot* instr) {
   ASSERT(instr->value()->representation().IsInteger32());
   ASSERT(instr->representation().IsInteger32());
+  if (instr->HasNoUses()) return NULL;
   LOperand* value = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new(zone()) LBitNotI(value));
 }

src/hydrogen-instructions.cc

@@ -870,6 +870,17 @@ HValue* HBitwise::Canonicalize() {
 }
 
 
+HValue* HBitNot::Canonicalize() {
+  // Optimize ~~x, a common pattern used for ToInt32(x).
+  if (value()->IsBitNot()) {
+    HValue* result = HBitNot::cast(value())->value();
+    ASSERT(result->representation().IsInteger32());
+    return result;
+  }
+  return this;
+}
+
+
 HValue* HAdd::Canonicalize() {
   if (!representation().IsInteger32()) return this;
   if (CheckUsesForFlag(kTruncatingToInt32)) ClearFlag(kCanOverflow);

src/hydrogen-instructions.h

@@ -1918,6 +1918,8 @@ class HBitNot: public HUnaryOperation {
   }
   virtual HType CalculateInferredType();
 
+  virtual HValue* Canonicalize();
+
   DECLARE_CONCRETE_INSTRUCTION(BitNot)
 
  protected:

src/ia32/lithium-ia32.cc

@@ -1330,6 +1330,7 @@ LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
 LInstruction* LChunkBuilder::DoBitNot(HBitNot* instr) {
   ASSERT(instr->value()->representation().IsInteger32());
   ASSERT(instr->representation().IsInteger32());
+  if (instr->HasNoUses()) return NULL;
   LOperand* input = UseRegisterAtStart(instr->value());
   LBitNotI* result = new(zone()) LBitNotI(input);
   return DefineSameAsFirst(result);

src/mips/lithium-mips.cc

@@ -1296,6 +1296,7 @@ LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
 LInstruction* LChunkBuilder::DoBitNot(HBitNot* instr) {
   ASSERT(instr->value()->representation().IsInteger32());
   ASSERT(instr->representation().IsInteger32());
+  if (instr->HasNoUses()) return NULL;
   LOperand* value = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new(zone()) LBitNotI(value));
 }

src/x64/lithium-x64.cc

@@ -1285,6 +1285,7 @@ LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
 LInstruction* LChunkBuilder::DoBitNot(HBitNot* instr) {
   ASSERT(instr->value()->representation().IsInteger32());
   ASSERT(instr->representation().IsInteger32());
+  if (instr->HasNoUses()) return NULL;
   LOperand* input = UseRegisterAtStart(instr->value());
   LBitNotI* result = new(zone()) LBitNotI(input);
   return DefineSameAsFirst(result);

test/mjsunit/compiler/optimize-bitnot.js

+// Copyright 2012 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 f(x) {
+  return ~~x;
+}
+
+f(42);
+f(42);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(42, f(42));
+assertEquals(42, f(42.5));
+assertEquals(1/0, 1/f(-0));
+assertEquals(-1, f(0xffffffff));
+assertEquals(0, f(undefined));
+assertEquals(0, f("abc"));