[turbofan] Utilize the fact that empty string is canonicalized.

src/compiler/effect-control-linearizer.cc

Index: src/compiler/effect-control-linearizer.cc
diff --git a/src/compiler/effect-control-linearizer.cc b/src/compiler/effect-control-linearizer.cc
index 10c982a7cbdff3d6726ce6f6b8ab9dde220d868b..dab5fac632ea1358011b1e7d55bf63f4e269cca1 100644
--- a/src/compiler/effect-control-linearizer.cc
+++ b/src/compiler/effect-control-linearizer.cc
@@ -922,70 +922,56 @@ Node* EffectControlLinearizer::LowerTruncateTaggedToBit(Node* node) {
   Node* value = node->InputAt(0);
 
   auto if_smi = __ MakeDeferredLabel<1>();
-  auto if_not_oddball = __ MakeDeferredLabel<1>();
-  auto if_not_string = __ MakeDeferredLabel<1>();
-  auto if_not_heapnumber = __ MakeDeferredLabel<1>();
-  auto done = __ MakeLabel<5>(MachineRepresentation::kBit);
+  auto if_heapnumber = __ MakeDeferredLabel<1>();
+  auto done = __ MakeLabel<6>(MachineRepresentation::kBit);
 
   Node* zero = __ Int32Constant(0);
   Node* fzero = __ Float64Constant(0.0);
 
+  // Check if {value} is false.
+  __ GotoIf(__ WordEqual(value, __ FalseConstant()), &done, zero);
+
   // Check if {value} is a Smi.
   Node* check_smi = ObjectIsSmi(value);
   __ GotoIf(check_smi, &if_smi);
 
-  // Load the map instance type of {value}.
+  // Check if {value} is the empty string.
+  __ GotoIf(__ WordEqual(value, __ EmptyStringConstant()), &done, zero);
+
+  // Load the map of {value}.
   Node* value_map = __ LoadField(AccessBuilder::ForMap(), value);
-  Node* value_instance_type =
-      __ LoadField(AccessBuilder::ForMapInstanceType(), value_map);
 
-  // Check if {value} is an Oddball.
-  Node* check_oddball =
-      __ Word32Equal(value_instance_type, __ Int32Constant(ODDBALL_TYPE));
-
-  __ GotoUnless(check_oddball, &if_not_oddball);
-  // The only Oddball {value} that is trueish is true itself.
-  __ Goto(&done, __ WordEqual(value, __ TrueConstant()));
-
-  __ Bind(&if_not_oddball);
-  // Check if {value} is a String.
-  Node* check_string = __ Int32LessThan(value_instance_type,
-                                        __ Int32Constant(FIRST_NONSTRING_TYPE));
-  __ GotoUnless(check_string, &if_not_string);
-  // For String {value}, we need to check that the length is not zero.
-  Node* value_length = __ LoadField(AccessBuilder::ForStringLength(), value);
-  __ Goto(&done, __ Word32Equal(
-                     __ WordEqual(value_length, __ IntPtrConstant(0)), zero));
-
-  __ Bind(&if_not_string);
-  // Check if {value} is a HeapNumber.
-  Node* check_heapnumber =
-      __ Word32Equal(value_instance_type, __ Int32Constant(HEAP_NUMBER_TYPE));
-  __ GotoUnless(check_heapnumber, &if_not_heapnumber);
-
-  // For HeapNumber {value}, just check that its value is not 0.0, -0.0 or
-  // NaN.
-  // Load the raw value of {value}.
-  Node* value_value = __ LoadField(AccessBuilder::ForHeapNumberValue(), value);
-  __ Goto(&done, __ Float64LessThan(fzero, __ Float64Abs(value_value)));
-
-  // The {value} is either a JSReceiver, a Symbol or some Simd128Value. In
-  // those cases we can just the undetectable bit on the map, which will only
-  // be set for certain JSReceivers, i.e. document.all.
-  __ Bind(&if_not_heapnumber);
-
-  // Load the {value} map bit field.
+  // Check if the {value} is undetectable and immediately return false.
   Node* value_map_bitfield =
       __ LoadField(AccessBuilder::ForMapBitField(), value_map);
-  __ Goto(&done, __ Word32Equal(
-                     __ Word32And(value_map_bitfield,
+  __ GotoUnless(
+      __ Word32Equal(__ Word32And(value_map_bitfield,
                                   __ Int32Constant(1 << Map::kIsUndetectable)),
-                     zero));
+                     zero),
+      &done, zero);
+
+  // Check if {value} is a HeapNumber.
+  __ GotoIf(__ WordEqual(value_map, __ HeapNumberMapConstant()),
+            &if_heapnumber);
+
+  // All other values that reach here are true.
+  __ Goto(&done, __ Int32Constant(1));
+
+  __ Bind(&if_heapnumber);
+  {
+    // For HeapNumber {value}, just check that its value is not 0.0, -0.0 or
+    // NaN.
+    Node* value_value =
+        __ LoadField(AccessBuilder::ForHeapNumberValue(), value);
+    __ Goto(&done, __ Float64LessThan(fzero, __ Float64Abs(value_value)));
+  }
 
   __ Bind(&if_smi);
-  // If {value} is a Smi, then we only need to check that it's not zero.
-  __ Goto(&done,
-          __ Word32Equal(__ WordEqual(value, __ IntPtrConstant(0)), zero));
+  {
+    // If {value} is a Smi, then we only need to check that it's not zero.
+    __ Goto(&done,
+            __ Word32Equal(__ WordEqual(value, __ IntPtrConstant(0)), zero));
+  }
 
   __ Bind(&done);
   return done.PhiAt(0);