Improve integer division on IA32 and X64

src/ia32/lithium-codegen-ia32.cc

 // 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
@@ skipping 1183 matching lines @@
 
     __ bind(&remainder_eq_dividend);
     __ mov(result_reg, left_reg);
 
     __ bind(&done);
   }
 }
 
 
 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) {

[Yang, 2012/12/10 09:47:28]

this if-block seems also unnecessary if divisor is -1 or 1

+      // 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));
   ASSERT(!ToRegister(instr->right()).is(eax));
   ASSERT(!ToRegister(instr->right()).is(edx));
 
   Register left_reg = eax;
 
   // Check for x / 0.
   Register right_reg = ToRegister(right);
   if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
     __ test(right_reg, ToOperand(right));
     DeoptimizeIf(zero, instr->environment());
   }
 
   // Check for (0 / -x) that will produce negative zero.
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     Label left_not_zero;
     __ test(left_reg, Operand(left_reg));
     __ j(not_zero, &left_not_zero, Label::kNear);
     __ test(right_reg, ToOperand(right));
     DeoptimizeIf(sign, instr->environment());
     __ 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);
     __ j(not_zero, &left_not_min_int, Label::kNear);
     __ cmp(right_reg, -1);
     DeoptimizeIf(zero, instr->environment());
     __ bind(&left_not_min_int);
   }
 
   // Sign extend to edx.
@@ skipping 4653 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32