Disable recompilation of existing Scripts from Isolate compilation cache

My previous change https://crrev.com/c/3597106 led to some performance
regressions in time spent on parsing and compilation. This change
disables the ability to recompile an existing uncompiled Script, as an
attempt to both fix the regressions and isolate which part of the
previous change was the cause of those problems.

Bug: v8:12808, chromium:1325566, chromium:1325567, chromium:1325601
Change-Id: Ifa086bf27070da8f4b3c0e4415af5ca7b6706b0a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3652252Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#80616}

src/codegen/compiler.cc

@@ -3043,7 +3043,9 @@ MaybeHandle<SharedFunctionInfo> GetSharedFunctionInfoForScriptImpl(
     // First check per-isolate compilation cache.
     CompilationCacheScript::LookupResult lookup_result =
         compilation_cache->LookupScript(source, script_details, language_mode);
-    maybe_script = lookup_result.script();
+    if (FLAG_isolate_script_cache_recompilation) {
+      maybe_script = lookup_result.script();
+    }
     maybe_result = lookup_result.toplevel_sfi();
     is_compiled_scope = lookup_result.is_compiled_scope();
     if (!maybe_result.is_null()) {

src/flags/flag-definitions.h

@@ -959,6 +959,9 @@ DEFINE_BOOL(turbo_collect_feedback_in_generic_lowering, true,
             "enable experimental feedback collection in generic lowering.")
 DEFINE_BOOL(isolate_script_cache_ageing, true,
             "enable ageing of the isolate script cache.")
+DEFINE_BOOL(isolate_script_cache_recompilation, false,
+            "enable recompiling an existing Script from the Isolate cache when "
+            "there is not a compiled top-level SharedFunctionInfo")
 
 DEFINE_FLOAT(script_delay, 0, "busy wait [ms] on every Script::Run")
 DEFINE_FLOAT(script_delay_once, 0, "busy wait [ms] on the first Script::Run")

test/cctest/heap/test-heap.cc

@@ -1578,6 +1578,12 @@ void CompilationCacheRegeneration(bool retain_root_sfi, bool flush_root_sfi,
     return;
   }
 
+  // If the compiler is configured to not recompile a flushed root SFI, then
+  // this test is invalid.
+  if (flush_root_sfi && !FLAG_isolate_script_cache_recompilation) {
+    return;
+  }
+
   // TODO(v8:12808): Remove this check once background compilation is capable of
   // reusing an existing Script.
   if (flush_root_sfi && FLAG_stress_background_compile) {

test/cctest/test-api.cc

@@ -23951,6 +23951,12 @@ TEST(StreamingWithIsolateScriptCacheClearingRootSFI) {
     return;
   }
 
+  // If the compiler is configured to not recompile a flushed root SFI, then
+  // this test is invalid.
+  if (!v8::internal::FLAG_isolate_script_cache_recompilation) {
+    return;
+  }
+
   StreamingWithIsolateScriptCache(true);
 }