[turbofan] Simplified lowering - introduce the concept of UseInfo.

src/compiler/representation-change.h

 // 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.
 
 #ifndef V8_COMPILER_REPRESENTATION_CHANGE_H_
 #define V8_COMPILER_REPRESENTATION_CHANGE_H_
 
 #include <sstream>
 
 #include "src/base/bits.h"
@@ skipping 34 matching lines @@
     if (IsWord(use_type) && IsWord(output_type)) {
       // Both are words less than or equal to 32-bits.
       // Since loads of integers from memory implicitly sign or zero extend the
       // value to the full machine word size and stores implicitly truncate,
       // no representation change is necessary.
       return node;
     }
     if (use_type & kRepTagged) {
       return GetTaggedRepresentationFor(node, output_type);
     } else if (use_type & kRepFloat32) {
-      return GetFloat32RepresentationFor(node, output_type);
+      return GetFloat32RepresentationFor(node, output_type, use_type);
     } else if (use_type & kRepFloat64) {
       return GetFloat64RepresentationFor(node, output_type, use_type);
     } else if (use_type & kRepBit) {
       return GetBitRepresentationFor(node, output_type);
     } else if (IsWord(use_type)) {
       return GetWord32RepresentationFor(node, output_type);
     } else if (use_type & kRepWord64) {
       return GetWord64RepresentationFor(node, output_type);
     } else {
       return node;
@@ skipping 42 matching lines @@
       node = InsertChangeFloat32ToFloat64(node);
       op = simplified()->ChangeFloat64ToTagged();
     } else if (output_type & kRepFloat64) {
       op = simplified()->ChangeFloat64ToTagged();
     } else {
       return TypeError(node, output_type, kRepTagged);
     }
     return jsgraph()->graph()->NewNode(op, node);
   }
 
-  Node* GetFloat32RepresentationFor(Node* node, MachineTypeUnion output_type) {
+  Node* GetFloat32RepresentationFor(Node* node, MachineTypeUnion output_type,
+                                    MachineTypeUnion truncation) {
     // Eagerly fold representation changes for constants.
     switch (node->opcode()) {
       case IrOpcode::kFloat64Constant:
       case IrOpcode::kNumberConstant:
         return jsgraph()->Float32Constant(
             DoubleToFloat32(OpParameter<double>(node)));
       case IrOpcode::kInt32Constant:
         if (output_type & kTypeUint32) {
           uint32_t value = static_cast<uint32_t>(OpParameter<int32_t>(node));
           return jsgraph()->Float32Constant(static_cast<float>(value));
         } else {
           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;
     if (output_type & kRepBit) {
       return TypeError(node, output_type, kRepFloat32);
     } else if (IsWord(output_type)) {
       if (output_type & kTypeUint32) {
         op = machine()->ChangeUint32ToFloat64();
       } else {
+        // Either the output is int32 or the uses only care about the
+        // low 32 bits (so we can pick int32 safely).
+        DCHECK(output_type & kTypeInt32 ||
+               !(truncation & ~(kTypeInt32 | kTypeUint32 | kRepMask)));
         op = machine()->ChangeInt32ToFloat64();
       }
       // int32 -> float64 -> float32
       node = jsgraph()->graph()->NewNode(op, node);
       op = machine()->TruncateFloat64ToFloat32();
     } else if (output_type & kRepTagged) {
       op = simplified()
                ->ChangeTaggedToFloat64();  // tagged -> float64 -> float32
       node = jsgraph()->graph()->NewNode(op, node);
       op = machine()->TruncateFloat64ToFloat32();
@@ skipping 314 matching lines @@
   Factory* factory() const { return isolate()->factory(); }
   SimplifiedOperatorBuilder* simplified() { return jsgraph()->simplified(); }
   MachineOperatorBuilder* machine() { return jsgraph()->machine(); }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_REPRESENTATION_CHANGE_H_