[turbofan][x64] Try harder to use memory addressing modes.

src/compiler/x64/instruction-selector-x64.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 <algorithm>
 
 #include "src/base/adapters.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
@@ skipping 136 matching lines @@
             m.index().Value() +
             (m.object().Value().address() - kRootsRegisterValue);
         if (is_int32(delta)) {
           inputs[(*input_count)++] = TempImmediate(static_cast<int32_t>(delta));
           return kMode_Root;
         }
       }
     }
     BaseWithIndexAndDisplacement64Matcher m(operand, AddressOption::kAllowAll);
     DCHECK(m.matches());
-    if ((m.displacement() == nullptr || CanBeImmediate(m.displacement()))) {
+    if (m.displacement() == nullptr || CanBeImmediate(m.displacement())) {
       return GenerateMemoryOperandInputs(
           m.index(), m.scale(), m.base(), m.displacement(),
           m.displacement_mode(), inputs, input_count);
+    } else if (m.base() == nullptr &&
+               m.displacement_mode() == kPositiveDisplacement) {
+      // The displacement cannot be an immediate, but we can use the
+      // displacement as base instead and still benefit from addressing
+      // modes for the scale.
+      return GenerateMemoryOperandInputs(m.index(), m.scale(), m.displacement(),
+                                         nullptr, m.displacement_mode(), inputs,
+                                         input_count);
     } else {
       inputs[(*input_count)++] = UseRegister(operand->InputAt(0));
       inputs[(*input_count)++] = UseRegister(operand->InputAt(1));
       return kMode_MR1;
     }
   }
 
   bool CanBeBetterLeftOperand(Node* node) const {
     return !selector()->IsLive(node);
   }
@@ skipping 2206 matching lines @@
 // static
 MachineOperatorBuilder::AlignmentRequirements
 InstructionSelector::AlignmentRequirements() {
   return MachineOperatorBuilder::AlignmentRequirements::
       FullUnalignedAccessSupport();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8