[turbofan] Generalize representation inference for NumberAdd.

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/base/bits.h"
 #include "src/code-factory.h"
@@ skipping 541 matching lines @@
   const Operator* Float64Op(Node* node) {
     return changer_->Float64OperatorFor(node->opcode());
   }
 
   bool CanLowerToInt32Binop(Node* node, Truncation use) {
     return BothInputsAre(node, Type::Signed32()) &&
            (use.TruncatesToWord32() ||
             NodeProperties::GetType(node)->Is(Type::Signed32()));
   }
 
-  bool CanLowerToWord32AdditiveBinop(Node* node, Truncation use) {
+  bool CanLowerToInt32AdditiveBinop(Node* node, Truncation use) {
+    // It is safe to lower to word32 operation if:
+    // - the inputs are safe integers (so the low bits are not discarded), and
+    // - the uses can only observe the lowest 32 bits or they can recover the
+    //   the value from the type.
+    // TODO(jarin): we could support the uint32 case here, but that would
+    // require setting kTypeUint32 as the output type. Eventually, we will want
+    // to use only the big types, then this should work automatically.
     return BothInputsAre(node, safe_int_additive_range_) &&
-           use.TruncatesToWord32();
+           (use.TruncatesToWord32() ||
+            NodeProperties::GetType(node)->Is(Type::Signed32()));
   }
 
   // Dispatching routine for visiting the node {node} with the usage {use}.
   // Depending on the operator, propagate new usage info to the inputs.
   void VisitNode(Node* node, Truncation truncation,
                  SimplifiedLowering* lowering) {
     switch (node->opcode()) {
       //------------------------------------------------------------------
       // Common operators.
       //------------------------------------------------------------------
@@ skipping 107 matching lines @@
           // => Float64Cmp
           VisitFloat64Cmp(node);
           if (lower()) NodeProperties::ChangeOp(node, Float64Op(node));
         }
         break;
       }
       case IrOpcode::kNumberAdd:
       case IrOpcode::kNumberSubtract: {
         // Add and subtract reduce to Int32Add/Sub if the inputs
         // are already integers and all uses are truncating.
-        if (CanLowerToWord32AdditiveBinop(node, truncation)) {
+        if (CanLowerToInt32AdditiveBinop(node, truncation)) {
           // => signed Int32Add/Sub
           VisitInt32Binop(node);
           if (lower()) NodeProperties::ChangeOp(node, Int32Op(node));
         } else {
           // => Float64Add/Sub
           VisitFloat64Binop(node);
           if (lower()) NodeProperties::ChangeOp(node, Float64Op(node));
         }
         break;
       }
@@ skipping 894 matching lines @@
   ReplaceEffectUses(node, comparison);
   node->ReplaceInput(0, comparison);
   node->ReplaceInput(1, jsgraph()->SmiConstant(EQUAL));
   node->TrimInputCount(2);
   NodeProperties::ChangeOp(node, machine()->IntLessThanOrEqual());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8