Implement flooring division by a constant via truncating division by a constant.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 49068e7fc7fce47392642fcdac98c5c419b1e0a6..d1c893dc88c39920ba1f7ba60e0d0aa619bfc6ef 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1160,8 +1160,31 @@ void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
     DeoptimizeIf(zero, instr->environment());
   }
 
-  // TODO(svenpanne) Add correction terms.
-  __ TruncatingDiv(dividend, divisor);
+  // Easy case: We need no dynamic check for the dividend and the flooring
+  // division is the same as the truncating division.
+  if ((divisor > 0 && !hdiv->CheckFlag(HValue::kLeftCanBeNegative)) ||
+      (divisor < 0 && !hdiv->CheckFlag(HValue::kLeftCanBePositive))) {
+    __ TruncatingDiv(dividend, Abs(divisor));
+    if (divisor < 0) __ negl(rdx);
+    return;
+  }
+
+  // In the general case we may need to adjust before and after the truncating
+  // division to get a flooring division.
+  Register temp = ToRegister(instr->temp3());
+  ASSERT(!temp.is(dividend) && !temp.is(rax) && !temp.is(rdx));
+  Label needs_adjustment, done;
+  __ cmpl(dividend, Immediate(0));
+  __ j(divisor > 0 ? less : greater, &needs_adjustment, Label::kNear);
+  __ TruncatingDiv(dividend, Abs(divisor));
+  if (divisor < 0) __ negl(rdx);
+  __ jmp(&done, Label::kNear);
+  __ bind(&needs_adjustment);
+  __ leal(temp, Operand(dividend, divisor > 0 ? 1 : -1));
+  __ TruncatingDiv(temp, Abs(divisor));
+  if (divisor < 0) __ negl(rdx);
+  __ decl(rdx);
+  __ bind(&done);
 }