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

src/mips/lithium-codegen-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.7
 // 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 1349 matching lines @@
     DeoptimizeIf(al, instr->environment());
     return;
   }
 
   // Check for (0 / -x) that will produce negative zero.
   HMathFloorOfDiv* hdiv = instr->hydrogen();
   if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) && divisor < 0) {
     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);
 }
 
 
 void LCodeGen::DoMulI(LMulI* instr) {
   Register scratch = scratch0();
   Register result = ToRegister(instr->result());
   // Note that result may alias left.
   Register left = ToRegister(instr->left());
   LOperand* right_op = instr->right();
 
@@ skipping 4406 matching lines @@
   __ Subu(scratch, result, scratch);
   __ lw(result, FieldMemOperand(scratch,
                                 FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal