Improve integer division on IA32 and X64

If the divisor is a Power-of-2 constant, we could use shifts instead of the
expensive idiv instructions, which also loose the register constraints.

Review URL: https://chromiumcodereview.appspot.com/11478043
Patch from Yuqiang Xian <yuqiang.xian@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13178 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -3683,6 +3683,16 @@ class HDiv: public HArithmeticBinaryOperation {
     SetFlag(kCanOverflow);
   }
 
+  bool HasPowerOf2Divisor() {
+    if (right()->IsConstant() &&
+        HConstant::cast(right())->HasInteger32Value()) {
+      int32_t value = HConstant::cast(right())->Integer32Value();
+      return value != 0 && (IsPowerOf2(value) || IsPowerOf2(-value));
+    }
+
+    return false;
+  }
+
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);
 
   static HInstruction* NewHDiv(Zone* zone,

src/ia32/lithium-codegen-ia32.cc

@@ -1201,6 +1201,43 @@ void LCodeGen::DoModI(LModI* instr) {
 
 
 void LCodeGen::DoDivI(LDivI* instr) {
+  if (instr->hydrogen()->HasPowerOf2Divisor()) {
+    Register dividend = ToRegister(instr->left());
+    int32_t divisor =
+        HConstant::cast(instr->hydrogen()->right())->Integer32Value();
+    int32_t test_value = 0;
+    int32_t power = 0;
+
+    if (divisor > 0) {
+      test_value = divisor - 1;
+      power = WhichPowerOf2(divisor);
+    } else {
+      // Check for (0 / -x) that will produce negative zero.
+      if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+        __ test(dividend, Operand(dividend));
+        DeoptimizeIf(zero, instr->environment());
+      }
+      // Check for (kMinInt / -1).
+      if (divisor == -1 && instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
+        __ cmp(dividend, kMinInt);
+        DeoptimizeIf(zero, instr->environment());
+      }
+      test_value = - divisor - 1;
+      power = WhichPowerOf2(-divisor);
+    }
+
+    if (test_value != 0) {
+      // Deoptimize if remainder is not 0.
+      __ test(dividend, Immediate(test_value));
+      DeoptimizeIf(not_zero, instr->environment());
+      __ sar(dividend, power);
+    }
+
+    if (divisor < 0) __ neg(dividend);
+
+    return;
+  }
+
   LOperand* right = instr->right();
   ASSERT(ToRegister(instr->result()).is(eax));
   ASSERT(ToRegister(instr->left()).is(eax));
@@ -1226,7 +1263,7 @@ void LCodeGen::DoDivI(LDivI* instr) {
     __ bind(&left_not_zero);
   }
 
-  // Check for (-kMinInt / -1).
+  // Check for (kMinInt / -1).
   if (instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
     Label left_not_min_int;
     __ cmp(left_reg, kMinInt);

src/ia32/lithium-ia32.cc

@@ -1264,6 +1264,13 @@ LInstruction* LChunkBuilder::DoDiv(HDiv* instr) {
   if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::DIV, instr);
   } else if (instr->representation().IsInteger32()) {
+    if (instr->HasPowerOf2Divisor()) {
+      ASSERT(!instr->CheckFlag(HValue::kCanBeDivByZero));
+      LOperand* value = UseRegisterAtStart(instr->left());
+      LDivI* div =
+          new(zone()) LDivI(value, UseOrConstant(instr->right()), NULL);
+      return AssignEnvironment(DefineSameAsFirst(div));
+    }
     // The temporary operand is necessary to ensure that right is not allocated
     // into edx.
     LOperand* temp = FixedTemp(edx);

src/x64/lithium-codegen-x64.cc

@@ -1133,6 +1133,43 @@ void LCodeGen::DoMathFloorOfDiv(LMathFloorOfDiv* instr) {
 
 
 void LCodeGen::DoDivI(LDivI* instr) {
+  if (instr->hydrogen()->HasPowerOf2Divisor()) {
+    Register dividend = ToRegister(instr->left());
+    int32_t divisor =
+        HConstant::cast(instr->hydrogen()->right())->Integer32Value();
+    int32_t test_value = 0;
+    int32_t power = 0;
+
+    if (divisor > 0) {
+      test_value = divisor - 1;
+      power = WhichPowerOf2(divisor);
+    } else {
+      // Check for (0 / -x) that will produce negative zero.
+      if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+        __ testl(dividend, dividend);
+        DeoptimizeIf(zero, instr->environment());
+      }
+      // Check for (kMinInt / -1).
+      if (divisor == -1 && instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
+        __ cmpl(dividend, Immediate(kMinInt));
+        DeoptimizeIf(zero, instr->environment());
+      }
+      test_value = - divisor - 1;
+      power = WhichPowerOf2(-divisor);
+    }
+
+    if (test_value != 0) {
+      // Deoptimize if remainder is not 0.
+      __ testl(dividend, Immediate(test_value));
+      DeoptimizeIf(not_zero, instr->environment());
+      __ sarl(dividend, Immediate(power));
+    }
+
+    if (divisor < 0) __ negl(dividend);
+
+    return;
+  }
+
   LOperand* right = instr->right();
   ASSERT(ToRegister(instr->result()).is(rax));
   ASSERT(ToRegister(instr->left()).is(rax));
@@ -1158,7 +1195,7 @@ void LCodeGen::DoDivI(LDivI* instr) {
     __ bind(&left_not_zero);
   }
 
-  // Check for (-kMinInt / -1).
+  // Check for (kMinInt / -1).
   if (instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
     Label left_not_min_int;
     __ cmpl(left_reg, Immediate(kMinInt));

src/x64/lithium-x64.cc

@@ -1187,6 +1187,13 @@ LInstruction* LChunkBuilder::DoDiv(HDiv* instr) {
   if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::DIV, instr);
   } else if (instr->representation().IsInteger32()) {
+    if (instr->HasPowerOf2Divisor()) {
+      ASSERT(!instr->CheckFlag(HValue::kCanBeDivByZero));
+      LOperand* value = UseRegisterAtStart(instr->left());
+      LDivI* div =
+          new(zone()) LDivI(value, UseOrConstant(instr->right()), NULL);
+      return AssignEnvironment(DefineSameAsFirst(div));
+    }
     // The temporary operand is necessary to ensure that right is not allocated
     // into rdx.
     LOperand* temp = FixedTemp(rdx);

test/mjsunit/shift-for-integer-div.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.
+
+function divp4(x) {
+  return x / 4;
+}
+
+for (var i = 0; i < 10000; i+=4) {
+  assertEquals(i >> 2, divp4(i));
+}
+
+assertEquals(0.5, divp4(2));
+
+function divn4(x) {
+  return x / (-4);
+}
+
+for (var i = 0; i < 10000; i+=4) {
+  assertEquals(-(i >> 2), divn4(i));
+}
+
+assertEquals(-0, divn4(0));
+
+
+function divn1(x) {
+  return x / (-1);
+}
+
+for (var i = 0; i < 10000; i++) {
+  assertEquals(-i, divn1(i));
+}
+
+var min_int = -(0x7FFFFFFF)-1;
+assertEquals(-min_int, divn1(min_int));
+