Improve integer division on IA32 and X64

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
===================================================================
--- src/x64/lithium-codegen-x64.cc	(revision 13175)
+++ src/x64/lithium-codegen-x64.cc	(working copy)
@@ -1133,6 +1133,43 @@
 
 
 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) {

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

Ditto.

+      // 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 @@
     __ 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));