[turbofan] Propagate minus-zero truncation in representation inference.

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"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node-matchers.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 const char* Truncation::description() const {
   switch (kind()) {
     case TruncationKind::kNone:
       return "no-value-use";
     case TruncationKind::kBool:
       return "truncate-to-bool";
     case TruncationKind::kWord32:
       return "truncate-to-word32";
     case TruncationKind::kWord64:
       return "truncate-to-word64";
     case TruncationKind::kFloat64:
-      return "truncate-to-float64";
+      switch (identify_zeros()) {
+        case kIdentifyZeros:
+          return "truncate-to-float64 (identify zeros)";
+        case kDistinguishZeros:
+          return "truncate-to-float64 (distinguish zeros)";
+      }
     case TruncationKind::kAny:
-      return "no-truncation";
+      switch (identify_zeros()) {
+        case kIdentifyZeros:
+          return "no-truncation (but identify zeros)";
+        case kDistinguishZeros:
+          return "no-truncation (but distinguish zeros)";
+      }
   }
   UNREACHABLE();
   return nullptr;
 }
 
 
 // Partial order for truncations:
 //
-//  kWord64       kAny
-//     ^            ^
-//     \            |
-//      \         kFloat64  <--+
+//  kWord64       kAny <-------+
+//     ^            ^          |
+//     \            |          |
+//      \         kFloat64     |
 //       \        ^            |
 //        \       /            |
 //         kWord32           kBool
 //               ^            ^
 //               \            /
 //                \          /
 //                 \        /
 //                  \      /
 //                   \    /
 //                   kNone
+//
+// TODO(jarin) We might consider making kBool < kFloat64.
 
 // static
 Truncation::TruncationKind Truncation::Generalize(TruncationKind rep1,
                                                   TruncationKind rep2) {
   if (LessGeneral(rep1, rep2)) return rep2;
   if (LessGeneral(rep2, rep1)) return rep1;
   // Handle the generalization of float64-representable values.
   if (LessGeneral(rep1, TruncationKind::kFloat64) &&
       LessGeneral(rep2, TruncationKind::kFloat64)) {
     return TruncationKind::kFloat64;
   }
   // Handle the generalization of any-representable values.
   if (LessGeneral(rep1, TruncationKind::kAny) &&
       LessGeneral(rep2, TruncationKind::kAny)) {
     return TruncationKind::kAny;
   }
   // All other combinations are illegal.
   FATAL("Tried to combine incompatible truncations");
   return TruncationKind::kNone;
 }
 
+// static
+IdentifyZeros Truncation::GeneralizeIdentifyZeros(IdentifyZeros i1,
+                                                  IdentifyZeros i2) {
+  if (i1 == i2) {
+    return i1;
+  } else {
+    return kDistinguishZeros;
+  }
+}
 
 // static
 bool Truncation::LessGeneral(TruncationKind rep1, TruncationKind rep2) {
   switch (rep1) {
     case TruncationKind::kNone:
       return true;
     case TruncationKind::kBool:
       return rep2 == TruncationKind::kBool || rep2 == TruncationKind::kAny;
     case TruncationKind::kWord32:
       return rep2 == TruncationKind::kWord32 ||
              rep2 == TruncationKind::kWord64 ||
              rep2 == TruncationKind::kFloat64 || rep2 == TruncationKind::kAny;
     case TruncationKind::kWord64:
       return rep2 == TruncationKind::kWord64;
     case TruncationKind::kFloat64:
       return rep2 == TruncationKind::kFloat64 || rep2 == TruncationKind::kAny;
     case TruncationKind::kAny:
       return rep2 == TruncationKind::kAny;
   }
   UNREACHABLE();
   return false;
 }
 
+// static
+bool Truncation::LessGeneralIdentifyZeros(IdentifyZeros i1, IdentifyZeros i2) {
+  return i1 == i2 || i1 == kIdentifyZeros;
+}
 
 namespace {
 
 bool IsWord(MachineRepresentation rep) {
   return rep == MachineRepresentation::kWord8 ||
          rep == MachineRepresentation::kWord16 ||
          rep == MachineRepresentation::kWord32;
 }
 
 }  // namespace
@@ skipping 936 matching lines @@
                                      node);
 }
 
 Node* RepresentationChanger::InsertChangeUint32ToFloat64(Node* node) {
   return jsgraph()->graph()->NewNode(machine()->ChangeUint32ToFloat64(), node);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8