Work towards objects stack allocation: moved allocation part of newobj-lowering into separate phase

1. Introduced `GT_ALLOCOBJ` node to mark places where object allocation happens
2. In `importer.cpp` changed lowering of allocation part of newobj instruction from an allocation helper call to a `GT_ALLOCOBJ` node creation
3. Created new phase `ObjectAllocator` (`PHASE_ALLOCATE_OBJECTS`) and put it right after dominator computing (we will need the information for escape analysis)
4. Current implementation of ObjectAllocator walks over all basic blocks having flag `BBF_HAS_NEWOBJ` set and replaces `GT_ALLOCOBJ` with  an allocation helper call

1 files changed, 86 insertions, 0 deletions

diff --git a/src/jit/objectalloc.h b/src/jit/objectalloc.h
new file mode 100644
index 0000000000..a9707f326d
--- /dev/null
+++ b/src/jit/objectalloc.h
@@ -0,0 +1,86 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+/*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+XX                                                                           XX
+XX                         ObjectAllocator                                   XX
+XX                                                                           XX
+XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+*/
+
+/*****************************************************************************/
+#ifndef OBJECTALLOC_H
+#define OBJECTALLOC_H
+/*****************************************************************************/
+
+//===============================================================================
+#include "phase.h"
+
+class ObjectAllocator final : public Phase
+{
+    //===============================================================================
+    // Data members
+    bool m_IsObjectStackAllocationEnabled;
+    bool m_AnalysisDone;
+    //===============================================================================
+    // Methods
+public:
+    ObjectAllocator(Compiler* comp);
+    bool IsObjectStackAllocationEnabled() const;
+    void EnableObjectStackAllocation();
+
+protected:
+    virtual void DoPhase() override;
+
+private:
+    bool CanAllocateLclVarOnStack(unsigned int lclNum) const;
+    void DoAnalysis();
+    void MorphAllocObjNodes();
+    GenTreePtr MorphAllocObjNodeIntoHelperCall(GenTreeAllocObj* allocObj);
+    GenTreePtr MorphAllocObjNodeIntoStackAlloc(GenTreeAllocObj* allocObj, BasicBlock* block, GenTreeStmt* stmt);
+#ifdef DEBUG
+    static Compiler::fgWalkResult AssertWhenAllocObjFoundVisitor(GenTreePtr* pTree, Compiler::fgWalkData* data);
+#endif // DEBUG
+};
+
+//===============================================================================
+
+inline
+ObjectAllocator::ObjectAllocator(Compiler* comp) :
+    Phase(comp, "Allocate Objects", PHASE_ALLOCATE_OBJECTS),
+    m_IsObjectStackAllocationEnabled(false),
+    m_AnalysisDone(false)
+{
+}
+
+inline
+bool ObjectAllocator::IsObjectStackAllocationEnabled() const
+{
+    return m_IsObjectStackAllocationEnabled;
+}
+
+inline
+void ObjectAllocator::EnableObjectStackAllocation()
+{
+    m_IsObjectStackAllocationEnabled = true;
+}
+
+//------------------------------------------------------------------------
+// CanAllocateLclVarOnStack: Returns true iff local variable can not
+//                           potentially escape from the method and
+//                           can be allocated on the stack.
+inline
+bool ObjectAllocator::CanAllocateLclVarOnStack(unsigned int lclNum) const
+{
+    assert(m_AnalysisDone);
+    // TODO-ObjectStackAllocation
+    NYI("CanAllocateLclVarOnStack");
+    return false;
+}
+
+//===============================================================================
+
+#endif // OBJECTALLOC_H