[Interpreter] Add a simple dead-code elimination bytecode optimizer.

src/flag-definitions.h

 // Copyright 2012 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.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 288 matching lines @@
 // Flags for data representation optimizations
 DEFINE_BOOL(unbox_double_arrays, true, "automatically unbox arrays of doubles")
 DEFINE_BOOL(string_slices, true, "use string slices")
 
 // Flags for Ignition.
 DEFINE_BOOL(ignition, false, "use ignition interpreter")
 DEFINE_BOOL(ignition_eager, false, "eagerly compile and parse with ignition")
 DEFINE_BOOL(ignition_generators, false,
             "enable experimental ignition support for generators")
 DEFINE_STRING(ignition_filter, "*", "filter for ignition interpreter")
+DEFINE_BOOL(ignition_deadcode, true,
+            "use ignition dead code elimination optimizer")
 DEFINE_BOOL(ignition_peephole, true, "use ignition peephole optimizer")
 DEFINE_BOOL(ignition_reo, true, "use ignition register equivalence optimizer")
 DEFINE_BOOL(ignition_filter_expression_positions, true,
             "filter expression positions before the bytecode pipeline")
 DEFINE_BOOL(print_bytecode, false,
             "print bytecode generated by ignition interpreter")
 DEFINE_BOOL(trace_ignition, false,
             "trace the bytecodes executed by the ignition interpreter")
 DEFINE_BOOL(trace_ignition_codegen, false,
             "trace the codegen of ignition interpreter bytecode handlers")
@@ skipping 872 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA