[ia32, root] Enable root register verification

Bug: v8:6666
Change-Id: I702ca633de56a5e1228f281de89e8bf7c12002a4
Reviewed-on: https://chromium-review.googlesource.com/c/1273077Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56517}

src/flag-definitions.h

@@ -1087,7 +1087,7 @@ DEFINE_BOOL_READONLY(embedded_builtins, V8_EMBEDDED_BUILTINS_BOOL,
                      "Embed builtin code into the binary.")
 // TODO(jgruber,v8:6666): Remove once ia32 has full embedded builtin support.
 DEFINE_BOOL_READONLY(
-    ia32_verify_root_register, false,
+    ia32_verify_root_register, V8_EMBEDDED_BUILTINS_BOOL,
     "Check that the value of the root register was not clobbered.")
 // TODO(jgruber,v8:6666): Remove once ia32 has full embedded builtin support.
 DEFINE_BOOL(print_embedded_builtin_candidates, false,

src/ia32/deoptimizer-ia32.cc

@@ -200,6 +200,8 @@ void Deoptimizer::TableEntryGenerator::Generate() {
   Assembler::AllowExplicitEbxAccessScope restoring_spilled_value(masm());
   __ popad();
 
+  __ InitializeRootRegister();
+
   // Return to the continuation point.
   __ ret(0);
 }