Fix and cleanup can_be_minus_zero computation

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // 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 1719 matching lines @@
   context()->PrintNameTo(stream);
 }
 
 
 Range* HValue::InferRange(Zone* zone) {
   Range* result;
   if (type().IsSmi()) {
     result = new(zone) Range(Smi::kMinValue, Smi::kMaxValue);
     result->set_can_be_minus_zero(false);
   } else {
-    // Untagged integer32 cannot be -0, all other representations can.
     result = new(zone) Range();
-    result->set_can_be_minus_zero(!representation().IsInteger32());
+    result->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32));
+    // TODO(jkummerow): The range cannot be minus zero when the upper type
+    // bound is Integer32.
   }
   return result;
 }
 
 
 Range* HChange::InferRange(Zone* zone) {
   Range* input_range = value()->range();
   if (from().IsInteger32() &&
       to().IsSmiOrTagged() &&
       !value()->CheckFlag(HInstruction::kUint32) &&
       input_range != NULL && input_range->IsInSmiRange()) {
     set_type(HType::Smi());
     ClearGVNFlag(kChangesNewSpacePromotion);
   }
   Range* result = (input_range != NULL)
       ? input_range->Copy(zone)
       : HValue::InferRange(zone);
-  if (to().IsInteger32()) result->set_can_be_minus_zero(false);
+  result->set_can_be_minus_zero(!to().IsSmiOrInteger32() ||
+                                !CheckFlag(kAllUsesTruncatingToInt32));
   return result;
 }
 
 
 Range* HConstant::InferRange(Zone* zone) {
   if (has_int32_value_) {
     Range* result = new(zone) Range(int32_value_, int32_value_);
     result->set_can_be_minus_zero(false);
     return result;
   }
@@ skipping 24 matching lines @@
 
 Range* HAdd::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
     Range* b = right()->range();
     Range* res = a->Copy(zone);
     if (!res->AddAndCheckOverflow(b) ||
         CheckFlag(kAllUsesTruncatingToInt32)) {
       ClearFlag(kCanOverflow);
     }
-    if (!CheckFlag(kAllUsesTruncatingToInt32)) {
-      res->set_can_be_minus_zero(a->CanBeMinusZero() && b->CanBeMinusZero());
-    }
+    res->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
+                               a->CanBeMinusZero() && b->CanBeMinusZero());
     return res;
   } else {
     return HValue::InferRange(zone);
   }
 }
 
 
 Range* HSub::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
     Range* b = right()->range();
     Range* res = a->Copy(zone);
     if (!res->SubAndCheckOverflow(b) ||
         CheckFlag(kAllUsesTruncatingToInt32)) {
       ClearFlag(kCanOverflow);
     }
-    if (!CheckFlag(kAllUsesTruncatingToInt32)) {
-      res->set_can_be_minus_zero(a->CanBeMinusZero() && b->CanBeZero());
-    }
+    res->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
+                               a->CanBeMinusZero() && b->CanBeZero());
     return res;
   } else {
     return HValue::InferRange(zone);
   }
 }
 
 
 Range* HMul::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
     Range* b = right()->range();
     Range* res = a->Copy(zone);
     if (!res->MulAndCheckOverflow(b)) {
       // Clearing the kCanOverflow flag when kAllUsesAreTruncatingToInt32
       // would be wrong, because truncated integer multiplication is too
       // precise and therefore not the same as converting to Double and back.
       ClearFlag(kCanOverflow);
     }
-    if (!CheckFlag(kAllUsesTruncatingToInt32)) {
-      bool m0 = (a->CanBeZero() && b->CanBeNegative()) ||
-          (a->CanBeNegative() && b->CanBeZero());
-      res->set_can_be_minus_zero(m0);
-    }
+    res->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
+                               ((a->CanBeZero() && b->CanBeNegative()) ||
+                                (a->CanBeNegative() && b->CanBeZero())));
     return res;
   } else {
     return HValue::InferRange(zone);
   }
 }
 
 
 Range* HDiv::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
     Range* b = right()->range();
     Range* result = new(zone) Range();
-    if (!CheckFlag(kAllUsesTruncatingToInt32)) {
-      if (a->CanBeMinusZero()) {
-        result->set_can_be_minus_zero(true);
-      }
-
-      if (a->CanBeZero() && b->CanBeNegative()) {
-        result->set_can_be_minus_zero(true);
-      }
-    }
-
+    result->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
+                                  (a->CanBeMinusZero() ||
+                                   (a->CanBeZero() && b->CanBeNegative())));
     if (!a->Includes(kMinInt) || !b->Includes(-1)) {
       ClearFlag(HValue::kCanOverflow);
     }
 
     if (!b->CanBeZero()) {
       ClearFlag(HValue::kCanBeDivByZero);
     }
     return result;
   } else {
     return HValue::InferRange(zone);
   }
 }
 
 
 Range* HMod::InferRange(Zone* zone) {
   if (representation().IsInteger32()) {
     Range* a = left()->range();
     Range* b = right()->range();
 
     // The magnitude of the modulus is bounded by the right operand. Note that
     // apart for the cases involving kMinInt, the calculation below is the same
     // as Max(Abs(b->lower()), Abs(b->upper())) - 1.
     int32_t positive_bound = -(Min(NegAbs(b->lower()), NegAbs(b->upper())) + 1);
 
     // The result of the modulo operation has the sign of its left operand.
     bool left_can_be_negative = a->CanBeMinusZero() || a->CanBeNegative();
     Range* result = new(zone) Range(left_can_be_negative ? -positive_bound : 0,
                                     a->CanBePositive() ? positive_bound : 0);
 
-    if (left_can_be_negative && !CheckFlag(kAllUsesTruncatingToInt32)) {
-      result->set_can_be_minus_zero(true);
-    }
+    result->set_can_be_minus_zero(!CheckFlag(kAllUsesTruncatingToInt32) &&
+                                  left_can_be_negative);
 
     if (!a->Includes(kMinInt) || !b->Includes(-1)) {
       ClearFlag(HValue::kCanOverflow);
     }
 
     if (!b->CanBeZero()) {
       ClearFlag(HValue::kCanBeDivByZero);
     }
     return result;
   } else {
@@ skipping 529 matching lines @@
           static_cast<uint32_t>(
               left_upper | left_lower | right_upper | right_lower));
 
       int64_t limit = 1;
       limit <<= high;
       int32_t min = (left()->range()->CanBeNegative() ||
                      right()->range()->CanBeNegative())
                     ? static_cast<int32_t>(-limit) : 0;
       return new(zone) Range(min, static_cast<int32_t>(limit - 1));
     }
-    return HValue::InferRange(zone);
+    Range* result = HValue::InferRange(zone);
+    result->set_can_be_minus_zero(false);
+    return result;
   }
   const int32_t kDefaultMask = static_cast<int32_t>(0xffffffff);
   int32_t left_mask = (left()->range() != NULL)
       ? left()->range()->Mask()
       : kDefaultMask;
   int32_t right_mask = (right()->range() != NULL)
       ? right()->range()->Mask()
       : kDefaultMask;
   int32_t result_mask = (op() == Token::BIT_AND)
       ? left_mask & right_mask
       : left_mask | right_mask;
-  return (result_mask >= 0)
-      ? new(zone) Range(0, result_mask)
-      : HValue::InferRange(zone);
+  if (result_mask >= 0) return new(zone) Range(0, result_mask);
+
+  Range* result = HValue::InferRange(zone);
+  result->set_can_be_minus_zero(false);
+  return result;
 }
 
 
 Range* HSar::InferRange(Zone* zone) {
   if (right()->IsConstant()) {
     HConstant* c = HConstant::cast(right());
     if (c->HasInteger32Value()) {
       Range* result = (left()->range() != NULL)
           ? left()->range()->Copy(zone)
           : new(zone) Range();
       result->Sar(c->Integer32Value());
-      result->set_can_be_minus_zero(false);
       return result;
     }
   }
   return HValue::InferRange(zone);
 }
 
 
 Range* HShr::InferRange(Zone* zone) {
   if (right()->IsConstant()) {
     HConstant* c = HConstant::cast(right());
     if (c->HasInteger32Value()) {
       int shift_count = c->Integer32Value() & 0x1f;
       if (left()->range()->CanBeNegative()) {
         // Only compute bounds if the result always fits into an int32.
         return (shift_count >= 1)
             ? new(zone) Range(0,
                               static_cast<uint32_t>(0xffffffff) >> shift_count)
             : new(zone) Range();
       } else {
         // For positive inputs we can use the >> operator.
         Range* result = (left()->range() != NULL)
             ? left()->range()->Copy(zone)
             : new(zone) Range();
         result->Sar(c->Integer32Value());
-        result->set_can_be_minus_zero(false);
         return result;
       }
     }
   }
   return HValue::InferRange(zone);
 }
 
 
 Range* HShl::InferRange(Zone* zone) {
   if (right()->IsConstant()) {
     HConstant* c = HConstant::cast(right());
     if (c->HasInteger32Value()) {
       Range* result = (left()->range() != NULL)
           ? left()->range()->Copy(zone)
           : new(zone) Range();
       result->Shl(c->Integer32Value());
-      result->set_can_be_minus_zero(false);
       return result;
     }
   }
   return HValue::InferRange(zone);
 }
 
 
 Range* HLoadKeyed::InferRange(Zone* zone) {
   switch (elements_kind()) {
     case EXTERNAL_PIXEL_ELEMENTS:
@@ skipping 1384 matching lines @@
     case kBackingStore:
       if (!name_.is_null()) stream->Add(*String::cast(*name_)->ToCString());
       stream->Add("[backing-store]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal