MIPS64: Port `ARM64: [turbofan] Avoid zero-extension after a 32-bit load`

src/compiler/mips64/instruction-selector-mips64.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/base/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 1192 matching lines @@
   } else {
     Mips64OperandGenerator g(this);
     Emit(kMips64Shl, g.DefineAsRegister(node), g.UseRegister(node->InputAt(0)),
          g.TempImmediate(0));
   }
 }
 
 
 void InstructionSelector::VisitChangeUint32ToUint64(Node* node) {
   Mips64OperandGenerator g(this);
+  Node* value = node->InputAt(0);
+  switch (value->opcode()) {
+    // 32-bit operations will write their result in a 64 bit register,
+    // clearing the top 32 bits of the destination register.
+    case IrOpcode::kUint32Div:
+    case IrOpcode::kUint32Mod:
+    case IrOpcode::kUint32MulHigh: {
+      Emit(kArchNop, g.DefineSameAsFirst(node), g.Use(value));
+      return;
+    }
+    case IrOpcode::kLoad: {
+      LoadRepresentation load_rep = LoadRepresentationOf(value->op());
+      if (load_rep.IsUnsigned()) {
+        switch (load_rep.representation()) {
+          case MachineRepresentation::kWord8:
+          case MachineRepresentation::kWord16:
+          case MachineRepresentation::kWord32:
+            Emit(kArchNop, g.DefineSameAsFirst(node), g.Use(value));
+            return;
+          default:
+            break;
+        }
+      }
+    }
+    default:
+      break;
+  }
   Emit(kMips64Dext, g.DefineAsRegister(node), g.UseRegister(node->InputAt(0)),
        g.TempImmediate(0), g.TempImmediate(32));
 }
 
 
 void InstructionSelector::VisitTruncateInt64ToInt32(Node* node) {
   Mips64OperandGenerator g(this);
   Node* value = node->InputAt(0);
   if (CanCover(node, value)) {
     switch (value->opcode()) {
@@ skipping 1269 matching lines @@
   } else {
     DCHECK(kArchVariant == kMips64r2);
     return MachineOperatorBuilder::AlignmentRequirements::
         NoUnalignedAccessSupport();
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8