Add a missing file from 225365

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225366 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/StatepointExampleGC.cpp

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+//===-- StatepointDefaultGC.cpp - The default statepoint GC strategy ------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains a GCStrategy which serves as an example for the usage
+// of a statepoint based lowering strategy.  This GCStrategy is intended to
+// suitable as a default implementation usable with any collector which can
+// consume the standard stackmap format generated by statepoints, uses the
+// default addrespace to distinguish between gc managed and non-gc managed
+// pointers, and has reasonable relocation semantics.  
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GCStrategy.h"
+#include "llvm/IR/Value.h"
+#include "llvm/IR/DerivedTypes.h"
+
+using namespace llvm;
+
+namespace {
+class StatepointGC : public GCStrategy {
+public:
+  StatepointGC() {
+    UseStatepoints = true;
+    // These options are all gc.root specific, we specify them so that the
+    // gc.root lowering code doesn't run.
+    InitRoots = false;
+    NeededSafePoints = 0;
+    UsesMetadata = false;
+    CustomRoots = false;
+    CustomSafePoints = false;
+  }
+  Optional<bool> isGCManagedPointer(const Value *V) const override {
+    // Method is only valid on pointer typed values.
+    PointerType *PT = cast<PointerType>(V->getType());
+    // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
+    // GC managed heap.  We know that a pointer into this heap needs to be
+    // updated and that no other pointer does.
+    return (1 == PT->getAddressSpace());
+  }
+};
+}
+
+static GCRegistry::Add<StatepointGC>
+X("statepoint-example", "an example strategy for statepoint");
+
+namespace llvm {
+void linkStatepointExampleGC() {}
+}