Fix TypeCheckingCache concurrency and candidate lifetime. (#6444)

* Fix TypeCheckingCache concurrency.

* Fix.

Author: csyonghe

source/slang/slang-check-overload.cpp

@@ -2565,7 +2565,7 @@ Expr* SemanticsVisitor::ResolveInvoke(InvokeExpr* expr)
                 // We should only use the cached candidate if it is persistent direct declref
                 // created from GlobalSession's ASTBuilder, or it is created in the current Linkage.
                 if (candidate.cacheVersion == typeCheckingCache->version ||
-                    as<DirectDeclRef>(candidate.candidate.item.declRef.declRefBase))
+                    findNextOuterGeneric(candidate.decl) == nullptr)
                 {
                     context.bestCandidateStorage = candidate.candidate;
                     context.bestCandidate = &context.bestCandidateStorage;

source/slang/slang-compiler.h

@@ -3591,6 +3591,7 @@ class Session : public RefObject, public slang::IGlobalSession
 
     RefPtr<RefObject> m_typeCheckingCache;
     TypeCheckingCache* getTypeCheckingCache();
+    std::mutex m_typeCheckingCacheMutex;
 
 private:
     struct BuiltinModuleInfo

source/slang/slang.cpp

@@ -809,9 +809,12 @@ Session::createSession(slang::SessionDesc const& inDesc, slang::ISession** outSe
 
     RefPtr<Linkage> linkage = new Linkage(this, astBuilder, getBuiltinLinkage());
 
-    if (m_typeCheckingCache)
-        linkage->m_typeCheckingCache =
-            new TypeCheckingCache(*static_cast<TypeCheckingCache*>(m_typeCheckingCache.get()));
+    {
+        std::lock_guard<std::mutex> lock(m_typeCheckingCacheMutex);
+        if (m_typeCheckingCache)
+            linkage->m_typeCheckingCache =
+                new TypeCheckingCache(*static_cast<TypeCheckingCache*>(m_typeCheckingCache.get()));
+    }
 
     linkage->setMatrixLayoutMode(desc.defaultMatrixLayoutMode);
 
@@ -1308,14 +1311,16 @@ Linkage::~Linkage()
     if (m_typeCheckingCache)
     {
         auto globalSession = getSessionImpl();
+        std::lock_guard<std::mutex> lock(globalSession->m_typeCheckingCacheMutex);
         if (!globalSession->m_typeCheckingCache ||
             globalSession->getTypeCheckingCache()->resolvedOperatorOverloadCache.getCount() <
                 getTypeCheckingCache()->resolvedOperatorOverloadCache.getCount())
         {
             globalSession->m_typeCheckingCache = m_typeCheckingCache;
+            getTypeCheckingCache()->version++;
         }
+        destroyTypeCheckingCache();
     }
-    destroyTypeCheckingCache();
 }
 
 SearchDirectoryList& Linkage::getSearchDirectories()