[compiler] Speculate a little more in SpeculativeShiftRightLogical.

src/compiler/simplified-lowering.cc

 // Copyright 2014 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 "src/compiler/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 1968 matching lines @@
         return;
       }
       case IrOpcode::kSpeculativeNumberShiftRightLogical: {
         // ToNumber(x) can throw if x is either a Receiver or a Symbol, so we
         // can only eliminate an unused speculative number operation if we know
         // that the inputs are PlainPrimitive, which excludes everything that's
         // might have side effects or throws during a ToNumber conversion.
         if (BothInputsAre(node, Type::PlainPrimitive())) {
           if (truncation.IsUnused()) return VisitUnused(node);
         }
+        NumberOperationHint hint = NumberOperationHintOf(node->op());
+        Type* rhs_type = GetUpperBound(node->InputAt(1));
+        STATIC_ASSERT(NumberOperationHint::kSignedSmall <=
+                      NumberOperationHint::kSigned32);
+        if (rhs_type->Is(type_cache_.kZeroish) &&
+            hint <= NumberOperationHint::kSigned32 &&

[Jarin, 2017/02/24 10:56:05]

In other places, we say "if (hint == NumberOperationHint::kSignedSmall || hint
== NumberOperationHint::kSigned32) ...". Could you keep this consistent?

+            !truncation.IsUsedAsWord32()) {
+          // The SignedSmall or Signed32 feedback means that the results that we
+          // have seen so far were of type Unsigned31.  We speculate that this
+          // will continue to hold.  Moreover, since the RHS is 0, the result
+          // will just be the (converted) LHS.
+          VisitBinop(node, CheckedUseInfoAsWord32FromHint(hint),
+                     MachineRepresentation::kWord32, Type::Unsigned31());
+          if (lower()) {
+            node->RemoveInput(1);
+            NodeProperties::ChangeOp(node,
+                                     simplified()->CheckedUint32ToInt32());
+          }
+          return;
+        }
         if (BothInputsAre(node, Type::NumberOrOddball())) {
-          Type* rhs_type = GetUpperBound(node->InputAt(1));
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
           if (lower()) {
             lowering->DoShift(node, lowering->machine()->Word32Shr(), rhs_type);
           }
           return;
         }
-        NumberOperationHint hint = NumberOperationHintOf(node->op());
-        Type* rhs_type = GetUpperBound(node->InputAt(1));
         VisitBinop(node, CheckedUseInfoAsWord32FromHint(hint),
                    MachineRepresentation::kWord32, Type::Unsigned32());
         if (lower()) {
           lowering->DoShift(node, lowering->machine()->Word32Shr(), rhs_type);
         }
         return;
       }
       case IrOpcode::kNumberAbs: {
         if (TypeOf(node->InputAt(0))->Is(Type::Unsigned32())) {
           VisitUnop(node, UseInfo::TruncatingWord32(),
@@ skipping 1505 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8