[ia32,root] Disable root indirections in irregexp code

Irregexp code spills and restores ebx at boundaries, and clobbers it
inbetween. Root-relative loads are disabled in this region.

Bug: v8:6666
Change-Id: I9c68bc8ef88d324da609996a8457ac9e30a9b6fc
Reviewed-on: https://chromium-review.googlesource.com/c/1280762Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56639}

src/regexp/ia32/regexp-macro-assembler-ia32.cc

@@ -85,6 +85,7 @@ RegExpMacroAssemblerIA32::RegExpMacroAssemblerIA32(Isolate* isolate, Zone* zone,
     : NativeRegExpMacroAssembler(isolate, zone),
       masm_(new MacroAssembler(isolate, nullptr, kRegExpCodeSize,
                                CodeObjectRequired::kYes)),
+      root_is_clobbered_(masm_),
       mode_(mode),
       num_registers_(registers_to_save),
       num_saved_registers_(registers_to_save),

src/regexp/ia32/regexp-macro-assembler-ia32.h

@@ -178,6 +178,9 @@ class RegExpMacroAssemblerIA32: public NativeRegExpMacroAssembler {
 
   MacroAssembler* masm_;
 
+  // Irregexp code clobbers the root register.
+  NoRootArrayScope root_is_clobbered_;
+
   // Which mode to generate code for (LATIN1 or UC16).
   Mode mode_;