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

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index e306c174cf7b62b0168ccfc6d249cc6359787969..5e47665c0c3c4298e33d898341f41f50642d00bc 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -1367,8 +1367,31 @@ void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
     DeoptimizeIf(eq, instr->environment(), dividend, Operand(zero_reg));
   }
 
-  // TODO(svenpanne) Add correction terms.
-  __ TruncatingDiv(result, 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(result, dividend, Abs(divisor));
+    if (divisor < 0) __ Subu(result, zero_reg, result);
+    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->temp());
+  ASSERT(!temp.is(dividend) && !temp.is(result));
+  Label needs_adjustment, done;
+  __ Branch(&needs_adjustment, divisor > 0 ? lt : gt,
+            dividend, Operand(zero_reg));
+  __ TruncatingDiv(result, dividend, Abs(divisor));
+  if (divisor < 0) __ Subu(result, zero_reg, result);
+  __ jmp(&done);
+  __ bind(&needs_adjustment);
+  __ Addu(temp, dividend, Operand(divisor > 0 ? 1 : -1));
+  __ TruncatingDiv(result, temp, Abs(divisor));
+  if (divisor < 0) __ Subu(result, zero_reg, result);
+  __ Subu(result, result, Operand(1));
+  __ bind(&done);
 }