More precise range analysis for smi multiplication.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/bit_vector.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 3067 matching lines @@
 
       if (!SymbolicSub(left_max, right_range->min(), &max)) {
         max =
           RangeBoundary::Sub(Range::ConstantMax(left_range),
                              Range::ConstantMin(right_range),
                              RangeBoundary::PositiveInfinity());
       }
       break;
 
     case Token::kMUL: {
       const int64_t left_max = ConstantAbsMax(left_range);

[Vyacheslav Egorov (Google), 2014/06/13 13:59:29]

Can you test it for kMinInt64 * -1? Because I am bit concerned about what
ConstantAbsMax(kMinInt64) returns. 

Similar for kMinSmi * -1.

[Florian Schneider, 2014/06/16 10:45:10]

We're staying in smi range here: ConstantAbsMax returns a value between 0 and
-kMinSmi, which is always smaller than kMaxInt.

       const int64_t right_max = ConstantAbsMax(right_range);
-      if ((left_max < 0x7FFFFFFF) && (right_max < 0x7FFFFFFF)) {
+      if ((left_max == 0) || (right_max <= kMaxInt64 / left_max)) {
         // Product of left and right max values stays in 64 bit range.
         const int64_t result_max = left_max * right_max;
         if (Smi::IsValid64(result_max) && Smi::IsValid64(-result_max)) {
           const intptr_t r_min =
               OnlyPositiveOrZero(left_range, right_range) ? 0 : -result_max;
           min = RangeBoundary::FromConstant(r_min);
           const intptr_t r_max =
               OnlyNegativeOrZero(left_range, right_range) ? 0 : result_max;
           max = RangeBoundary::FromConstant(r_max);
           break;
@@ skipping 486 matching lines @@
     case Token::kTRUNCDIV: return 0;
     case Token::kMOD: return 1;
     default: UNIMPLEMENTED(); return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart