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

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 70 matching lines @@
     case kExternalFloat32Array:
       return MachineRepresentation::kFloat32;
     case kExternalFloat64Array:
       return MachineRepresentation::kFloat64;
   }
   UNREACHABLE();
   return MachineRepresentation::kNone;
 }
 
 UseInfo CheckedUseInfoAsWord32FromHint(
-    NumberOperationHint hint, CheckForMinusZeroMode minus_zero_mode =
-                                  CheckForMinusZeroMode::kCheckForMinusZero) {
+    NumberOperationHint hint,
+    IdentifyZeros identify_zeros = kDistinguishZeros) {
   switch (hint) {
     case NumberOperationHint::kSignedSmall:
-      return UseInfo::CheckedSignedSmallAsWord32(minus_zero_mode);
+      return UseInfo::CheckedSignedSmallAsWord32(identify_zeros);
     case NumberOperationHint::kSigned32:
-      return UseInfo::CheckedSigned32AsWord32(minus_zero_mode);
+      return UseInfo::CheckedSigned32AsWord32(identify_zeros);
     case NumberOperationHint::kNumber:
       return UseInfo::CheckedNumberAsWord32();
     case NumberOperationHint::kNumberOrOddball:
       return UseInfo::CheckedNumberOrOddballAsWord32();
   }
   UNREACHABLE();
   return UseInfo::None();
 }
 
 UseInfo CheckedUseInfoAsFloat64FromHint(NumberOperationHint hint) {
@@ skipping 1052 matching lines @@
   CommonOperatorBuilder* common() const { return jsgraph_->common(); }
   SimplifiedOperatorBuilder* simplified() const {
     return jsgraph_->simplified();
   }
 
   void LowerToCheckedInt32Mul(Node* node, Truncation truncation,
                               Type* input0_type, Type* input1_type) {
     // If one of the inputs is positive and/or truncation is being applied,
     // there is no need to return -0.
     CheckForMinusZeroMode mz_mode =
-        truncation.IsUsedAsWord32() ||
+        truncation.IdentifiesZeroAndMinusZero() ||
                 (input0_type->Is(Type::OrderedNumber()) &&
                  input0_type->Min() > 0) ||
                 (input1_type->Is(Type::OrderedNumber()) &&
                  input1_type->Min() > 0)
             ? CheckForMinusZeroMode::kDontCheckForMinusZero
             : CheckForMinusZeroMode::kCheckForMinusZero;
 
     NodeProperties::ChangeOp(node, simplified()->CheckedInt32Mul(mz_mode));
   }
 
@@ skipping 38 matching lines @@
       // Handle the case when no int32 checks on inputs are necessary (but
       // an overflow check is needed on the output).
       // TODO(jarin) We should not look at the upper bound because the typer
       // could have already baked in some feedback into the upper bound.
       if (BothInputsAre(node, Type::Signed32()) ||
           (BothInputsAre(node, Type::Signed32OrMinusZero()) &&
            GetUpperBound(node)->Is(type_cache_.kSafeInteger))) {
         VisitBinop(node, UseInfo::TruncatingWord32(),
                    MachineRepresentation::kWord32, Type::Signed32());
       } else {
-        UseInfo left_use = CheckedUseInfoAsWord32FromHint(hint);
+        IdentifyZeros lhs_identify_zeros = truncation.identify_zeros();

[Benedikt Meurer, 2017/03/08 03:56:53]

Nit: left instead of lbs for consistency.

[Jarin, 2017/03/08 05:46:51]

Done.

+        if (node->opcode() == IrOpcode::kSpeculativeNumberAdd &&

[Benedikt Meurer, 2017/03/08 03:56:53]

This deserves a comment, maybe just repeating the example from the CL
description.

[Jarin, 2017/03/08 05:46:51]

Done.

+            !right_feedback_type->Maybe(Type::MinusZero())) {
+          lhs_identify_zeros = kIdentifyZeros;
+        }
+        UseInfo left_use =
+            CheckedUseInfoAsWord32FromHint(hint, lhs_identify_zeros);
         // For CheckedInt32Add and CheckedInt32Sub, we don't need to do
         // a minus zero check for the right hand side, since we already
         // know that the left hand side is a proper Signed32 value,
         // potentially guarded by a check.
-        UseInfo right_use = CheckedUseInfoAsWord32FromHint(
-            hint, CheckForMinusZeroMode::kDontCheckForMinusZero);
+        UseInfo right_use =
+            CheckedUseInfoAsWord32FromHint(hint, kIdentifyZeros);
         VisitBinop(node, left_use, right_use, MachineRepresentation::kWord32,
                    Type::Signed32());
       }
       if (lower()) {
         if (CanOverflowSigned32(node->op(), left_feedback_type,
                                 right_feedback_type, graph_zone())) {
           ChangeToInt32OverflowOp(node);
         } else {
           ChangeToPureOp(node, Int32Op(node));
         }
@@ skipping 1027 matching lines @@
         Type* length_type = TypeOf(node->InputAt(1));
         if (index_type->Is(Type::Unsigned32())) {
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
           if (lower() && index_type->Max() < length_type->Min()) {
             // The bounds check is redundant if we already know that
             // the index is within the bounds of [0.0, length[.
             DeferReplacement(node, node->InputAt(0));
           }
         } else {
-          VisitBinop(node, UseInfo::CheckedSigned32AsWord32(),
+          VisitBinop(node, UseInfo::CheckedSigned32AsWord32(kIdentifyZeros),
                      UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
         }
         return;
       }
       case IrOpcode::kCheckHeapObject: {
         if (InputCannotBe(node, Type::SignedSmall())) {
           VisitUnop(node, UseInfo::AnyTagged(),
                     MachineRepresentation::kTaggedPointer);
         } else {
@@ skipping 45 matching lines @@
                     MachineRepresentation::kTaggedPointer);
           if (lower()) DeferReplacement(node, node->InputAt(0));
         } else {
           VisitUnop(node, UseInfo::CheckedHeapObjectAsTaggedPointer(),
                     MachineRepresentation::kTaggedPointer);
         }
         return;
       }
       case IrOpcode::kCheckSmi: {
         if (SmiValuesAre32Bits() && truncation.IsUsedAsWord32()) {
-          VisitUnop(node, UseInfo::CheckedSignedSmallAsWord32(),
+          VisitUnop(node,
+                    UseInfo::CheckedSignedSmallAsWord32(kDistinguishZeros),
                     MachineRepresentation::kWord32);
         } else {
           VisitUnop(node, UseInfo::CheckedSignedSmallAsTaggedSigned(),
                     MachineRepresentation::kTaggedSigned);
         }
         if (lower()) DeferReplacement(node, node->InputAt(0));
         return;
       }
       case IrOpcode::kCheckString: {
         if (InputIs(node, Type::String())) {
@@ skipping 1210 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