[turbofan] Handle impossible types (Type::None()) in the backend.

src/compiler/representation-change.cc

 // Copyright 2015 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/representation-change.h"
 
 #include <sstream>
 
 #include "src/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 99 matching lines @@
 
 }  // namespace
 
 // Changes representation from {output_rep} to {use_rep}. The {truncation}
 // parameter is only used for sanity checking - if the changer cannot figure
 // out signedness for the word32->float64 conversion, then we check that the
 // uses truncate to word32 (so they do not care about signedness).
 Node* RepresentationChanger::GetRepresentationFor(
     Node* node, MachineRepresentation output_rep, Type* output_type,
     Node* use_node, UseInfo use_info) {
-  if (output_rep == MachineRepresentation::kNone) {
-    // The output representation should be set.
+  if (output_rep == MachineRepresentation::kNone &&
+      output_type->IsInhabited()) {
+    // The output representation should be set if the type is inhabited (i.e.,
+    // if the value is possible).
     return TypeError(node, output_rep, output_type, use_info.representation());
   }
 
   // Handle the no-op shortcuts when no checking is necessary.
   if (use_info.type_check() == TypeCheckKind::kNone ||
       output_rep != MachineRepresentation::kWord32) {
     if (use_info.representation() == output_rep) {
       // Representations are the same. That's a no-op.
       return node;
     }
@@ skipping 61 matching lines @@
       }
     case IrOpcode::kFloat64Constant:
       return jsgraph()->Constant(OpParameter<double>(node));
     case IrOpcode::kFloat32Constant:
       return jsgraph()->Constant(OpParameter<float>(node));
     default:
       break;
   }
   // Select the correct X -> Tagged operator.
   const Operator* op;
-  if (output_rep == MachineRepresentation::kBit) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only asisgn this representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToTagged();
+  } else if (output_rep == MachineRepresentation::kBit) {
     if (output_type->Is(Type::Boolean())) {
       op = simplified()->ChangeBitToTagged();
     } else {
       return TypeError(node, output_rep, output_type,
                        MachineRepresentation::kTagged);
     }
   } else if (IsWord(output_rep)) {
     if (output_type->Is(Type::Signed31())) {
       op = simplified()->ChangeInt31ToTaggedSigned();
     } else if (output_type->Is(Type::Signed32())) {
@@ skipping 50 matching lines @@
         int32_t value = OpParameter<int32_t>(node);
         return jsgraph()->Float32Constant(static_cast<float>(value));
       }
     case IrOpcode::kFloat32Constant:
       return node;  // No change necessary.
     default:
       break;
   }
   // Select the correct X -> Float32 operator.
   const Operator* op = nullptr;
-  if (IsWord(output_rep)) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToFloat32();
+  } else if (IsWord(output_rep)) {
     if (output_type->Is(Type::Signed32())) {
       // int32 -> float64 -> float32
       op = machine()->ChangeInt32ToFloat64();
       node = jsgraph()->graph()->NewNode(op, node);
       op = machine()->TruncateFloat64ToFloat32();
     } else if (output_type->Is(Type::Unsigned32()) ||
                truncation.IsUsedAsWord32()) {
       // Either the output is uint32 or the uses only care about the
       // low 32 bits (so we can pick uint32 safely).
 
@@ skipping 44 matching lines @@
       case IrOpcode::kFloat64Constant:
         return node;  // No change necessary.
       case IrOpcode::kFloat32Constant:
         return jsgraph()->Float64Constant(OpParameter<float>(node));
       default:
         break;
     }
   }
   // Select the correct X -> Float64 operator.
   const Operator* op = nullptr;
-  if (IsWord(output_rep)) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToFloat64();
+  } else if (IsWord(output_rep)) {
     if (output_type->Is(Type::Signed32())) {
       op = machine()->ChangeInt32ToFloat64();
     } else if (output_type->Is(Type::Unsigned32()) ||
                use_info.truncation().IsUsedAsWord32()) {
       // Either the output is uint32 or the uses only care about the
       // low 32 bits (so we can pick uint32 safely).
       op = machine()->ChangeUint32ToFloat64();
     }
   } else if (output_rep == MachineRepresentation::kBit) {
     op = machine()->ChangeUint32ToFloat64();
@@ skipping 51 matching lines @@
         return MakeTruncatedInt32Constant(fv);
       }
       break;
     }
     default:
       break;
   }
 
   // Select the correct X -> Word32 operator.
   const Operator* op = nullptr;
-  if (output_rep == MachineRepresentation::kBit) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToWord32();
+  } else if (output_rep == MachineRepresentation::kBit) {
     return node;  // Sloppy comparison -> word32
   } else if (output_rep == MachineRepresentation::kFloat64) {
     if (output_type->Is(Type::Unsigned32())) {
       op = machine()->ChangeFloat64ToUint32();
     } else if (output_type->Is(Type::Signed32())) {
       op = machine()->ChangeFloat64ToInt32();
     } else if (use_info.truncation().IsUsedAsWord32()) {
       op = machine()->TruncateFloat64ToWord32();
     } else if (use_info.type_check() == TypeCheckKind::kSigned32) {
       op = simplified()->CheckedFloat64ToInt32();
@@ skipping 68 matching lines @@
       DCHECK(value.is_identical_to(factory()->true_value()) ||
              value.is_identical_to(factory()->false_value()));
       return jsgraph()->Int32Constant(
           value.is_identical_to(factory()->true_value()) ? 1 : 0);
     }
     default:
       break;
   }
   // Select the correct X -> Bit operator.
   const Operator* op;
-  if (output_rep == MachineRepresentation::kTagged) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToBit();
+  } else if (output_rep == MachineRepresentation::kTagged) {
     op = simplified()->ChangeTaggedToBit();
   } else {
     return TypeError(node, output_rep, output_type,
                      MachineRepresentation::kBit);
   }
   return jsgraph()->graph()->NewNode(op, node);
 }
 
 Node* RepresentationChanger::GetWord64RepresentationFor(
     Node* node, MachineRepresentation output_rep, Type* output_type) {
-  if (output_rep == MachineRepresentation::kBit) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    return jsgraph()->graph()->NewNode(machine()->ImpossibleToFloat64(), node);
+  } else if (output_rep == MachineRepresentation::kBit) {
     return node;  // Sloppy comparison -> word64
   }
   // Can't really convert Word64 to anything else. Purported to be internal.
   return TypeError(node, output_rep, output_type,
                    MachineRepresentation::kWord64);
 }
 
 Node* RepresentationChanger::GetCheckedWord32RepresentationFor(
     Node* node, MachineRepresentation output_rep, Type* output_type,
     Node* use_node, Truncation truncation, TypeCheckKind check) {
   // TODO(jarin) Eagerly fold constants (or insert hard deopt if the constant
   // does not pass the check).
 
   // If the input is already Signed32 in Word32 representation, we do not
   // have to do anything. (We could fold this into the big if below, but
   // it feels nicer to have the shortcut return first).
   if (output_rep == MachineRepresentation::kWord32 ||
       output_type->Is(Type::Signed32())) {
     return node;
   }
 
   // Select the correct X -> Word32 operator.
   const Operator* op = nullptr;
-  if (output_rep == MachineRepresentation::kWord32) {
+  if (output_rep == MachineRepresentation::kNone) {
+    // We should only use kNone representation if the type is empty.
+    CHECK(!output_type->IsInhabited());
+    op = machine()->ImpossibleToWord32();
+  } else if (output_rep == MachineRepresentation::kWord32) {
     if (output_type->Is(Type::Unsigned32())) {
       op = simplified()->CheckedUint32ToInt32();
     }
   } else if (output_rep == MachineRepresentation::kBit) {
     return node;  // Sloppy comparison -> word32
   } else if (output_rep == MachineRepresentation::kFloat64) {
     if (output_type->Is(Type::Unsigned32())) {
       op = machine()->ChangeFloat64ToUint32();
     } else if (output_type->Is(Type::Signed32())) {
       op = machine()->ChangeFloat64ToInt32();
@@ skipping 268 matching lines @@
 }
 
 Node* RepresentationChanger::InsertChangeTaggedToFloat64(Node* node) {
   return jsgraph()->graph()->NewNode(simplified()->ChangeTaggedToFloat64(),
                                      node);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8