MIPS: Fixed flooring division by -1.

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 1304 matching lines @@
   }
 
   // If the divisor is negative, we have to negate and handle edge cases.
   if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
     __ Move(scratch, dividend);
   }
   __ Subu(result, zero_reg, dividend);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    __ Xor(at, scratch, result);
-    if (divisor == -1) {
-      DeoptimizeIf(ge, instr->environment(), at, Operand(zero_reg));
-      __ sra(result, dividend, shift);
-    } else {
-      Label no_overflow, done;
-      __ Branch(&no_overflow, lt, at, Operand(zero_reg));
-      __ li(result, Operand(kMinInt / divisor));
-      __ Branch(&done);
-      __ bind(&no_overflow);
-      __ sra(result, dividend, shift);
-      __ bind(&done);
-    }
-  } else {
+
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
     __ sra(result, dividend, shift);
+    return;
   }
+
+  // Dividing by -1 is basically negation, unless we overflow.
+  __ Xor(at, scratch, result);
+  if (divisor == -1) {
+    DeoptimizeIf(ge, instr->environment(), at, Operand(zero_reg));
+    return;
+  }
+
+  Label no_overflow, done;
+  __ Branch(&no_overflow, lt, at, Operand(zero_reg));
+  __ li(result, Operand(kMinInt / divisor));
+  __ Branch(&done);
+  __ bind(&no_overflow);
+  __ sra(result, dividend, shift);
+  __ bind(&done);
 }
 
 
 void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
   Register dividend = ToRegister(instr->dividend());
   int32_t divisor = instr->divisor();
   Register result = ToRegister(instr->result());
   ASSERT(!dividend.is(result));
 
   if (divisor == 0) {
@@ skipping 4552 matching lines @@
   __ lw(result, FieldMemOperand(scratch,
                                 FixedArray::kHeaderSize - kPointerSize));
   __ bind(deferred->exit());
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal