[gn] Rework debug configurations

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
+import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 import("gni/v8.gni")
 import("gni/isolate.gni")
 import("//build_overrides/v8.gni")
@@ skipping 16 matching lines @@
   # Sets -dENABLE_GDB_JIT_INTERFACE.
   v8_enable_gdbjit = false
 
   # Sets -dENABLE_HANDLE_ZAPPING.
   v8_enable_handle_zapping = true
 
   # Enable ECMAScript Internationalization API. Enabling this feature will
   # add a dependency on the ICU library.
   v8_enable_i18n_support = true
 
+  # Enable slow dchecks.
+  v8_enable_slow_dchecks = false
+
   # Interpreted regexp engine exists as platform-independent alternative
   # based where the regular expression is compiled to a bytecode.
   v8_interpreted_regexp = false
 
   # Sets -dOBJECT_PRINT.
   v8_object_print = false
 
+  # Turns on compiler optimizations in V8 in Debug build.
+  v8_optimized_debug = true
+
   # With post mortem support enabled, metadata is embedded into libv8 that
   # describes various parameters of the VM for use by debuggers. See
   # tools/gen-postmortem-metadata.py for details.
   v8_postmortem_support = false
 
   # Similar to vfp but on MIPS.
   v8_can_use_fpu_instructions = true
 
   # Similar to the ARM hard float ABI but on MIPS.
   v8_use_mips_abi_hardfloat = true
@@ skipping 220 matching lines @@
   if (is_debug) {
     # TODO(jochen): Add support for different debug optimization levels.
     defines += [
       "ENABLE_DISASSEMBLER",
       "V8_ENABLE_CHECKS",
       "OBJECT_PRINT",
       "VERIFY_HEAP",
       "DEBUG",
       "TRACE_MAPS",
     ]
-    if (!v8_optimized_debug) {
+    if (v8_enable_slow_dchecks) {
       defines += [ "ENABLE_SLOW_DCHECKS" ]
     }
+  } else if (dcheck_always_on) {
+    defines += [ "DEBUG" ]
   }
 }
 
 ###############################################################################
 # Templates
 #
 
 template("v8_source_set") {
   source_set(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
     configs += [
       ":features",
       ":toolchain",
     ]
 
-    if (!is_debug || v8_optimized_debug) {
+    # TODO(machenbach): This config doesn't affect executables and components.
+    # It should be moved to a common place.
+    if (is_debug && !v8_optimized_debug) {
+      configs -= [ "//build/config/compiler:default_optimization" ]
+      configs += [ "//build/config/compiler:no_optimize" ]
+    } else {
       configs -= [ "//build/config/compiler:default_optimization" ]
       configs += [ "//build/config/compiler:optimize_max" ]
     }
   }
 }
 
 ###############################################################################
 # Actions
 #
 
@@ skipping 1948 matching lines @@
   ]
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }
 
 v8_fuzzer("wasm_asmjs_fuzzer") {}