MIPS64: Fix TruncatingDiv.

src/mips64/macro-assembler-mips64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_MIPS64
 
@@ skipping 6049 matching lines @@
   masm_.emit(instr);
 }
 
 
 void MacroAssembler::TruncatingDiv(Register result,
                                    Register dividend,
                                    int32_t divisor) {
   DCHECK(!dividend.is(result));
   DCHECK(!dividend.is(at));
   DCHECK(!result.is(at));
   base::MagicNumbersForDivision<uint32_t> mag =

[dusmil.imgtec, 2014/10/08 09:56:40]

Can we instantiate template class with int32_t parameter here?
Will it cause to much trouble to change this?

[Sven Panne, 2014/10/08 10:44:13]

Nope, the template parameter *must* be unsigned, otherwise all this stuff is
wrong. With full C++11 support I would have added

   static_assert(std::is_unsigned<T>, "T must be unsigned");

to base::MagicNumbersForDivision, but we're not there yet, so there's only a
comment. Furthermore, we only have only instantiations for uint32_t and
uint64_t, so you would get a linker error reminding you of that fact. :-)

   base::SignedDivisionByConstant(static_cast<uint32_t>(divisor));
-  li(at, Operand(mag.multiplier));
+  li(at, Operand(static_cast<int32_t>(mag.multiplier)));
   Mulh(result, dividend, Operand(at));
   bool neg = (mag.multiplier & (static_cast<uint32_t>(1) << 31)) != 0;
   if (divisor > 0 && neg) {
     Addu(result, result, Operand(dividend));
   }
   if (divisor < 0 && !neg && mag.multiplier > 0) {
     Subu(result, result, Operand(dividend));
   }
   if (mag.shift > 0) sra(result, result, mag.shift);
   srl(at, dividend, 31);
   Addu(result, result, Operand(at));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS64