Add MachineModuleInfo constructor with external MCContext

Adds a constructor to MachineModuleInfo and MachineModuleInfoWapperPass that
takes an external MCContext. If provided, the external context will be used
throughout codegen instead of MMI's default one.

This enables external drivers to take ownership of data put on the MMI's context
during codegen. The internal context is used otherwise and destroyed upon
finish.

Differential Revision: https://reviews.llvm.org/D91313

llvm/include/llvm/CodeGen/MachineModuleInfo.h

@@ -83,6 +83,9 @@ class MachineModuleInfo {
 
   /// This is the MCContext used for the entire code generator.
   MCContext Context;
+  // This is an external context, that if assigned, will be used instead of the
+  // internal context.
+  MCContext *ExternalContext = nullptr;
 
   /// This is the LLVM Module being worked on.
   const Module *TheModule;
@@ -149,6 +152,9 @@ class MachineModuleInfo {
 public:
   explicit MachineModuleInfo(const LLVMTargetMachine *TM = nullptr);
 
+  explicit MachineModuleInfo(const LLVMTargetMachine *TM,
+                             MCContext *ExtContext);
+
   MachineModuleInfo(MachineModuleInfo &&MMII);
 
   ~MachineModuleInfo();
@@ -158,8 +164,12 @@ public:
 
   const LLVMTargetMachine &getTarget() const { return TM; }
 
-  const MCContext &getContext() const { return Context; }
-  MCContext &getContext() { return Context; }
+  const MCContext &getContext() const {
+    return ExternalContext ? *ExternalContext : Context;
+  }
+  MCContext &getContext() {
+    return ExternalContext ? *ExternalContext : Context;
+  }
 
   const Module *getModule() const { return TheModule; }
 
@@ -266,6 +276,9 @@ public:
   static char ID; // Pass identification, replacement for typeid
   explicit MachineModuleInfoWrapperPass(const LLVMTargetMachine *TM = nullptr);
 
+  explicit MachineModuleInfoWrapperPass(const LLVMTargetMachine *TM,
+                                        MCContext *ExtContext);
+
   // Initialization and Finalization
   bool doInitialization(Module &) override;
   bool doFinalization(Module &) override;

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -170,6 +170,7 @@ void MachineModuleInfo::finalize() {
   AddrLabelSymbols = nullptr;
 
   Context.reset();
+  // We don't clear the ExternalContext.
 
   delete ObjFileMMI;
   ObjFileMMI = nullptr;
@@ -187,6 +188,7 @@ MachineModuleInfo::MachineModuleInfo(MachineModuleInfo &&MMI)
   HasSplitStack = MMI.HasSplitStack;
   HasNosplitStack = MMI.HasNosplitStack;
   AddrLabelSymbols = MMI.AddrLabelSymbols;
+  ExternalContext = MMI.ExternalContext;
   TheModule = MMI.TheModule;
 }
 
@@ -196,6 +198,14 @@ MachineModuleInfo::MachineModuleInfo(const LLVMTargetMachine *TM)
   initialize();
 }
 
+MachineModuleInfo::MachineModuleInfo(const LLVMTargetMachine *TM,
+                                     MCContext *ExtContext)
+    : TM(*TM), Context(TM->getMCAsmInfo(), TM->getMCRegisterInfo(),
+                       TM->getObjFileLowering(), nullptr, nullptr, false),
+      ExternalContext(ExtContext) {
+  initialize();
+}
+
 MachineModuleInfo::~MachineModuleInfo() { finalize(); }
 
 //===- Address of Block Management ----------------------------------------===//
@@ -204,7 +214,7 @@ ArrayRef<MCSymbol *>
 MachineModuleInfo::getAddrLabelSymbolToEmit(const BasicBlock *BB) {
   // Lazily create AddrLabelSymbols.
   if (!AddrLabelSymbols)
-    AddrLabelSymbols = new MMIAddrLabelMap(Context);
+    AddrLabelSymbols = new MMIAddrLabelMap(getContext());
  return AddrLabelSymbols->getAddrLabelSymbolToEmit(const_cast<BasicBlock*>(BB));
 }
 
@@ -296,6 +306,12 @@ MachineModuleInfoWrapperPass::MachineModuleInfoWrapperPass(
   initializeMachineModuleInfoWrapperPassPass(*PassRegistry::getPassRegistry());
 }
 
+MachineModuleInfoWrapperPass::MachineModuleInfoWrapperPass(
+    const LLVMTargetMachine *TM, MCContext *ExtContext)
+    : ImmutablePass(ID), MMI(TM, ExtContext) {
+  initializeMachineModuleInfoWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
 // Handle the Pass registration stuff necessary to use DataLayout's.
 INITIALIZE_PASS(MachineModuleInfoWrapperPass, "machinemoduleinfo",
                 "Machine Module Information", false, false)