[ORC] Remove the automagic Main JITDylib fram ExecutionSession.

This patch removes the magic "main" JITDylib from ExecutionEngine. The main
JITDylib was created automatically at ExecutionSession construction time, and
all subsequently created JITDylibs were added to the main JITDylib's
links-against list by default. This saves a couple of lines of boilerplate for
simple JIT setups, but this isn't worth introducing magical behavior for.

ORCv2 clients should now construct their own main JITDylib using
ExecutionSession::createJITDylib and set up its linkages manually using
JITDylib::setSearchOrder (or related methods in JITDylib).

3 files changed, 4 insertions, 13 deletions

diff --git a/llvm/lib/ExecutionEngine/Orc/CompileOnDemandLayer.cpp b/llvm/lib/ExecutionEngine/Orc/CompileOnDemandLayer.cpp
index b8e42922027..f26835ff8a0 100644
--- a/llvm/lib/ExecutionEngine/Orc/CompileOnDemandLayer.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/CompileOnDemandLayer.cpp
@@ -172,8 +172,8 @@ CompileOnDemandLayer::PerDylibResources &
 CompileOnDemandLayer::getPerDylibResources(JITDylib &TargetD) {
   auto I = DylibResources.find(&TargetD);
   if (I == DylibResources.end()) {
-    auto &ImplD = getExecutionSession().createJITDylib(
-        TargetD.getName() + ".impl", false);
+    auto &ImplD =
+        getExecutionSession().createJITDylib(TargetD.getName() + ".impl");
     TargetD.withSearchOrderDo(
         [&](const JITDylibSearchOrder &TargetSearchOrder) {
           auto NewSearchOrder = TargetSearchOrder;
diff --git a/llvm/lib/ExecutionEngine/Orc/Core.cpp b/llvm/lib/ExecutionEngine/Orc/Core.cpp
index 0814ec1c5f8..63ef889dae4 100644
--- a/llvm/lib/ExecutionEngine/Orc/Core.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/Core.cpp
@@ -1854,12 +1854,6 @@ void JITDylib::transferEmittedNodeDependencies(
 
 ExecutionSession::ExecutionSession(std::shared_ptr<SymbolStringPool> SSP)
     : SSP(SSP ? std::move(SSP) : std::make_shared<SymbolStringPool>()) {
-  // Construct the main dylib.
-  JDs.push_back(std::unique_ptr<JITDylib>(new JITDylib(*this, "<main>")));
-}
-
-JITDylib &ExecutionSession::getMainJITDylib() {
-  return runSessionLocked([this]() -> JITDylib & { return *JDs.front(); });
 }
 
 JITDylib *ExecutionSession::getJITDylibByName(StringRef Name) {
@@ -1871,14 +1865,11 @@ JITDylib *ExecutionSession::getJITDylibByName(StringRef Name) {
   });
 }
 
-JITDylib &ExecutionSession::createJITDylib(std::string Name,
-                                           bool AddToMainDylibSearchOrder) {
+JITDylib &ExecutionSession::createJITDylib(std::string Name) {
   assert(!getJITDylibByName(Name) && "JITDylib with that name already exists");
   return runSessionLocked([&, this]() -> JITDylib & {
     JDs.push_back(
         std::unique_ptr<JITDylib>(new JITDylib(*this, std::move(Name))));
-    if (AddToMainDylibSearchOrder)
-      JDs.front()->addToSearchOrder(*JDs.back());
     return *JDs.back();
   });
 }
diff --git a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
index fb5515ca64d..89dad6d61b4 100644
--- a/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/LLJIT.cpp
@@ -105,7 +105,7 @@ LLJIT::createCompileFunction(LLJITBuilderState &S,
 
 LLJIT::LLJIT(LLJITBuilderState &S, Error &Err)
     : ES(S.ES ? std::move(S.ES) : std::make_unique<ExecutionSession>()),
-      Main(this->ES->getMainJITDylib()), DL(""),
+      Main(this->ES->createJITDylib("<main>")), DL(""),
       ObjLinkingLayer(createObjectLinkingLayer(S, *ES)),
       ObjTransformLayer(*this->ES, *ObjLinkingLayer), CtorRunner(Main),
       DtorRunner(Main) {