[gin] Add flag for eliding redundant TDZ checks in Ignition

Bug: v8:13723
Change-Id: I332215c76b5f64514ea5c8e7a9cdccf210839c47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4523612
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1142886}

diff --git a/gin/gin_features.cc b/gin/gin_features.cc
index 96714e6..fef95f01 100644
--- a/gin/gin_features.cc
+++ b/gin/gin_features.cc

@@ -152,6 +152,12 @@
              "V8UseLibmTrigFunctions",
              base::FEATURE_ENABLED_BY_DEFAULT);
 
+// Elide redundant TDZ hole checks in bytecode. This only sets the V8 flag when
+// manually overridden.
+BASE_FEATURE(kV8IgnitionElideRedundantTdzChecks,
+             "V8IgnitionElideRedundantTdzChecks",
+             base::FEATURE_ENABLED_BY_DEFAULT);
+
 // JavaScript language features.
 
 // Enables the Symbols-as-WeakMap-keys proposal.

diff --git a/gin/gin_features.h b/gin/gin_features.h
index 7399e408..e0cc3c4f 100644
--- a/gin/gin_features.h
+++ b/gin/gin_features.h

@@ -25,6 +25,7 @@
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8FlushBaselineCode);
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8FlushBytecode);
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8FlushEmbeddedBlobICache);
+GIN_EXPORT BASE_DECLARE_FEATURE(kV8IgnitionElideRedundantTdzChecks);
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8LazyFeedbackAllocation);
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8Maglev);
 GIN_EXPORT BASE_DECLARE_FEATURE(kV8MinorMC);

diff --git a/gin/v8_initializer.cc b/gin/v8_initializer.cc
index ee54275..0ea2663 100644
--- a/gin/v8_initializer.cc
+++ b/gin/v8_initializer.cc

@@ -333,6 +333,10 @@
                            "--no-slow-histograms");
   }
 
+  SetV8FlagsIfOverridden(features::kV8IgnitionElideRedundantTdzChecks,
+                         "--ignition-elide-redundant-tdz-checks",
+                         "--no-ignition-elide-redundant-tdz-checks");
+
   // JavaScript language features.
   SetV8FlagsIfOverridden(features::kJavaScriptSymbolAsWeakMapKey,
                          "--harmony-symbol-as-weakmap-key",