[turbofan] Introduce ChangeTaggedToTaggedSigned operator.

We were missing a case for Tagged->TaggedSigned conversions when the
input type is known to be Type::SignedSmall.

BUG=chromium:687029
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2666863002
Cr-Commit-Position: refs/heads/master@{#42809}

src/compiler/effect-control-linearizer.cc

@@ -633,6 +633,9 @@ bool EffectControlLinearizer::TryWireInStateEffect(Node* node,
     case IrOpcode::kChangeTaggedToFloat64:
       result = LowerChangeTaggedToFloat64(node);
       break;
+    case IrOpcode::kChangeTaggedToTaggedSigned:
+      result = LowerChangeTaggedToTaggedSigned(node);
+      break;
     case IrOpcode::kTruncateTaggedToBit:
       result = LowerTruncateTaggedToBit(node);
       break;
@@ -1032,6 +1035,27 @@ Node* EffectControlLinearizer::LowerChangeTaggedToFloat64(Node* node) {
   return LowerTruncateTaggedToFloat64(node);
 }
 
+Node* EffectControlLinearizer::LowerChangeTaggedToTaggedSigned(Node* node) {
+  Node* value = node->InputAt(0);
+
+  auto if_not_smi = __ MakeDeferredLabel<1>();
+  auto done = __ MakeLabel<2>(MachineRepresentation::kWord32);
+
+  Node* check = ObjectIsSmi(value);
+  __ GotoUnless(check, &if_not_smi);
+  __ Goto(&done, value);
+
+  __ Bind(&if_not_smi);
+  STATIC_ASSERT(HeapNumber::kValueOffset == Oddball::kToNumberRawOffset);
+  Node* vfalse = __ LoadField(AccessBuilder::ForHeapNumberValue(), value);
+  vfalse = __ ChangeFloat64ToInt32(vfalse);
+  vfalse = ChangeInt32ToSmi(vfalse);
+  __ Goto(&done, vfalse);
+
+  __ Bind(&done);
+  return done.PhiAt(0);
+}
+
 Node* EffectControlLinearizer::LowerTruncateTaggedToFloat64(Node* node) {
   Node* value = node->InputAt(0);
 

src/compiler/effect-control-linearizer.h

@@ -51,6 +51,7 @@ class V8_EXPORT_PRIVATE EffectControlLinearizer {
   Node* LowerChangeTaggedToBit(Node* node);
   Node* LowerChangeTaggedToInt32(Node* node);
   Node* LowerChangeTaggedToUint32(Node* node);
+  Node* LowerChangeTaggedToTaggedSigned(Node* node);
   Node* LowerCheckBounds(Node* node, Node* frame_state);
   Node* LowerCheckInternalizedString(Node* node, Node* frame_state);
   Node* LowerCheckMaps(Node* node, Node* frame_state);

src/compiler/opcodes.h

@@ -191,6 +191,7 @@
   V(ChangeTaggedToInt32)             \
   V(ChangeTaggedToUint32)            \
   V(ChangeTaggedToFloat64)           \
+  V(ChangeTaggedToTaggedSigned)      \
   V(ChangeInt31ToTaggedSigned)       \
   V(ChangeInt32ToTagged)             \
   V(ChangeUint32ToTagged)            \

src/compiler/representation-change.cc

@@ -271,9 +271,15 @@ Node* RepresentationChanger::GetTaggedSignedRepresentationFor(
       return TypeError(node, output_rep, output_type,
                        MachineRepresentation::kTaggedSigned);
     }
-  } else if (CanBeTaggedPointer(output_rep) &&
-             use_info.type_check() == TypeCheckKind::kSignedSmall) {
-    op = simplified()->CheckedTaggedToTaggedSigned();
+  } else if (CanBeTaggedPointer(output_rep)) {
+    if (use_info.type_check() == TypeCheckKind::kSignedSmall) {
+      op = simplified()->CheckedTaggedToTaggedSigned();
+    } else if (output_type->Is(Type::SignedSmall())) {
+      op = simplified()->ChangeTaggedToTaggedSigned();
+    } else {
+      return TypeError(node, output_rep, output_type,
+                       MachineRepresentation::kTaggedSigned);
+    }
   } else if (output_rep == MachineRepresentation::kBit &&
              use_info.type_check() == TypeCheckKind::kSignedSmall) {
     // TODO(turbofan): Consider adding a Bailout operator that just deopts.

src/compiler/simplified-operator.cc

@@ -469,6 +469,7 @@ UnicodeEncoding UnicodeEncodingOf(const Operator* op) {
   V(ChangeTaggedToInt32, Operator::kNoProperties, 1, 0)          \
   V(ChangeTaggedToUint32, Operator::kNoProperties, 1, 0)         \
   V(ChangeTaggedToFloat64, Operator::kNoProperties, 1, 0)        \
+  V(ChangeTaggedToTaggedSigned, Operator::kNoProperties, 1, 0)   \
   V(ChangeFloat64ToTagged, Operator::kNoProperties, 1, 0)        \
   V(ChangeFloat64ToTaggedPointer, Operator::kNoProperties, 1, 0) \
   V(ChangeInt31ToTaggedSigned, Operator::kNoProperties, 1, 0)    \

src/compiler/simplified-operator.h

@@ -366,6 +366,7 @@ class V8_EXPORT_PRIVATE SimplifiedOperatorBuilder final
   const Operator* ChangeTaggedToInt32();
   const Operator* ChangeTaggedToUint32();
   const Operator* ChangeTaggedToFloat64();
+  const Operator* ChangeTaggedToTaggedSigned();
   const Operator* ChangeInt31ToTaggedSigned();
   const Operator* ChangeInt32ToTagged();
   const Operator* ChangeUint32ToTagged();

src/compiler/verifier.cc

@@ -1012,6 +1012,8 @@ void Verifier::Visitor::Check(Node* node) {
       // CheckTypeIs(node, to));
       break;
     }
+    case IrOpcode::kChangeTaggedToTaggedSigned:
+      break;
     case IrOpcode::kTruncateTaggedToFloat64: {
       // NumberOrUndefined /\ Tagged -> Number /\ UntaggedFloat64
       // TODO(neis): Activate once ChangeRepresentation works in typer.

test/mjsunit/regress/regress-crbug-687029.js

@@ -0,0 +1,14 @@
+// Copyright 2017 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.
+
+// Flags: --allow-natives-syntax
+
+function foo(x) {
+  x = Math.clz32(x);
+  return "a".indexOf("a", x);
+}
+foo(1);
+foo(1);
+%OptimizeFunctionOnNextCall(foo);
+foo();