[regexp] Add --trace-regexp-graph

Until now we've only exposed trace output for the parse- and assembly
stages of regexp codegen. Debug tracing of the graph was missing. The
new --trace-regexp-graph flag fills that hole.

Available regexp codegen tracing flags are now:

--trace-regexp-parser
--trace-regexp-graph
--trace-regexp-assembler

The output of --trace-regexp-graph can be formatted with `dot`, for
example:

 $ d8 --trace-regexp-graph [...] | dot -Tjpg -o regexp-graph.jpg

Change-Id: Ice593c34f7818c94e42d98e98a31533178bb538b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2808945
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73825}

src/flags/flag-definitions.h

@@ -1610,6 +1610,7 @@ DEFINE_BOOL(trace_regexp_assembler, false,
             "trace regexp macro assembler calls.")
 DEFINE_BOOL(trace_regexp_parser, false, "trace regexp parsing")
 DEFINE_BOOL(trace_regexp_tier_up, false, "trace regexp tiering up execution")
+DEFINE_BOOL(trace_regexp_graph, false, "trace the regexp graph")
 
 DEFINE_BOOL(enable_experimental_regexp_engine, false,
             "recognize regexps with 'l' flag, run them on experimental engine")

src/regexp/regexp-dotprinter.cc

@@ -13,8 +13,6 @@ namespace internal {
 // -------------------------------------------------------------------
 // Dot/dotty output
 
-#ifdef DEBUG
-
 class DotPrinterImpl : public NodeVisitor {
  public:
   explicit DotPrinterImpl(std::ostream& os) : os_(os) {}
@@ -239,14 +237,10 @@ void DotPrinterImpl::VisitAction(ActionNode* that) {
   Visit(successor);
 }
 
-#endif  // DEBUG
-
 void DotPrinter::DotPrint(const char* label, RegExpNode* node) {
-#ifdef DEBUG
   StdoutStream os;
   DotPrinterImpl printer(os);
   printer.PrintNode(label, node);
-#endif  // DEBUG
 }
 
 }  // namespace internal

src/regexp/regexp.cc

@@ -821,6 +821,8 @@ bool RegExpImpl::Compile(Isolate* isolate, Zone* zone, RegExpCompileData* data,
     return false;
   }
 
+  if (FLAG_trace_regexp_graph) DotPrinter::DotPrint("Start", data->node);
+
   // Create the correct assembler for the architecture.
   std::unique_ptr<RegExpMacroAssembler> macro_assembler;
   if (data->compilation_target == RegExpCompilationTarget::kNative) {