From 13cfc1a2343e4adafae12614eb39721c36f91266 Mon Sep 17 00:00:00 2001
From: Boris Ulasevich <Boris.Ulasevich@bell-sw.com>
Date: Wed, 24 Apr 2024 06:23:55 +0000
Subject: [PATCH] release C1 scratch buffer after compilation

---
 src/hotspot/share/c1/c1_Compiler.cpp         | 31 ++++++++++++++++----
 src/hotspot/share/c1/c1_Compiler.hpp         |  1 +
 src/hotspot/share/compiler/compileBroker.cpp |  6 ----
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/src/hotspot/share/c1/c1_Compiler.cpp b/src/hotspot/share/c1/c1_Compiler.cpp
index bdbeb39f89a4a..fae904c515729 100644
--- a/src/hotspot/share/c1/c1_Compiler.cpp
+++ b/src/hotspot/share/c1/c1_Compiler.cpp
@@ -62,10 +62,9 @@ void Compiler::init_c1_runtime() {
 
 
 void Compiler::initialize() {
-  // Buffer blob must be allocated per C1 compiler thread at startup
-  BufferBlob* buffer_blob = init_buffer_blob();
-
+  // MonitorLocker only_one(CompileThread_lock);
   if (should_perform_init()) {
+    BufferBlob* buffer_blob = init_buffer_blob();
     if (buffer_blob == nullptr) {
       // When we come here we are in state 'initializing'; entire C1 compilation
       // can be shut down.
@@ -74,6 +73,8 @@ void Compiler::initialize() {
       init_c1_runtime();
       set_state(initialized);
     }
+    tty->print_cr("## Compiler::initialize -> c1_init");
+    release_buffer_blob();
   }
 }
 
@@ -82,8 +83,6 @@ uint Compiler::code_buffer_size() {
 }
 
 BufferBlob* Compiler::init_buffer_blob() {
-  // Allocate buffer blob once at startup since allocation for each
-  // compilation seems to be too expensive (at least on Intel win32).
   assert (CompilerThread::current()->get_buffer_blob() == nullptr, "Should initialize only once");
 
   // setup CodeBuffer.  Preallocate a BufferBlob of size
@@ -96,6 +95,18 @@ BufferBlob* Compiler::init_buffer_blob() {
   return buffer_blob;
 }
 
+void Compiler::release_buffer_blob() {
+  BufferBlob* buffer_blob = CompilerThread::current()->get_buffer_blob();
+  if (buffer_blob != nullptr) {
+    CompilerThread::current()->set_buffer_blob(nullptr);
+    // Note.
+    // free_buffer_blob_if_allocated does the following. Why?
+    //   blob->purge(true /* free_code_cache_data */, true /* unregister_nmethod */);
+    //   MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+    BufferBlob::free(buffer_blob);
+  }
+}
+
 bool Compiler::is_intrinsic_supported(const methodHandle& method) {
   vmIntrinsics::ID id = method->intrinsic_id();
   assert(id != vmIntrinsics::_none, "must be a VM intrinsic");
@@ -247,7 +258,13 @@ bool Compiler::is_intrinsic_supported(vmIntrinsics::ID id) {
 
 void Compiler::compile_method(ciEnv* env, ciMethod* method, int entry_bci, bool install_code, DirectiveSet* directive) {
   BufferBlob* buffer_blob = CompilerThread::current()->get_buffer_blob();
-  assert(buffer_blob != nullptr, "Must exist");
+  if (buffer_blob == nullptr) { buffer_blob = init_buffer_blob(); }
+
+  if (buffer_blob == nullptr) {
+    warning("no space to run C1 compiler");
+    return;
+  }
+
   // invoke compilation
   {
     // We are nested here because we need for the destructor
@@ -256,6 +273,8 @@ void Compiler::compile_method(ciEnv* env, ciMethod* method, int entry_bci, bool
     ResourceMark rm;
     Compilation c(this, env, method, entry_bci, buffer_blob, install_code, directive);
   }
+
+  release_buffer_blob();
 }
 
 
diff --git a/src/hotspot/share/c1/c1_Compiler.hpp b/src/hotspot/share/c1/c1_Compiler.hpp
index 0160ee6357471..c5d77571f28c4 100644
--- a/src/hotspot/share/c1/c1_Compiler.hpp
+++ b/src/hotspot/share/c1/c1_Compiler.hpp
@@ -35,6 +35,7 @@ class Compiler: public AbstractCompiler {
  private:
   static void init_c1_runtime();
   BufferBlob* init_buffer_blob();
+  void release_buffer_blob();
 
  public:
   // Creation
diff --git a/src/hotspot/share/compiler/compileBroker.cpp b/src/hotspot/share/compiler/compileBroker.cpp
index 7adb4dfc587e1..b29453a4d75ef 100644
--- a/src/hotspot/share/compiler/compileBroker.cpp
+++ b/src/hotspot/share/compiler/compileBroker.cpp
@@ -1787,12 +1787,6 @@ bool CompileBroker::init_compiler_runtime() {
     return false;
   }
 
-  // C1 specific check
-  if (comp->is_c1() && (thread->get_buffer_blob() == nullptr)) {
-    warning("Initialization of %s thread failed (no space to run compilers)", thread->name());
-    return false;
-  }
-
   return true;
 }