Reland of [turbofan] Insert dummy values when changing from None type.

src/compiler/x64/code-generator-x64.cc

 // Copyright 2013 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/code-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 848 matching lines @@
       AssembleArchTableSwitch(instr);
       break;
     case kArchComment: {
       Address comment_string = i.InputExternalReference(0).address();
       __ RecordComment(reinterpret_cast<const char*>(comment_string));
       break;
     }
     case kArchDebugBreak:
       __ int3();
       break;
-    case kArchImpossible:
-      __ Abort(kConversionFromImpossibleValue);
-      break;
     case kArchNop:
     case kArchThrowTerminator:
       // don't emit code for nops.
       break;
     case kArchDeoptimize: {
       int deopt_state_id =
           BuildTranslation(instr, -1, 0, OutputFrameStateCombine::Ignore());
       Deoptimizer::BailoutType bailout_type =
           Deoptimizer::BailoutType(MiscField::decode(instr->opcode()));
       CodeGenResult result =
@@ skipping 1791 matching lines @@
     int padding_size = last_lazy_deopt_pc_ + space_needed - current_pc;
     __ Nop(padding_size);
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8