Introduce an example statepoint GC strategy

This change includes the most basic possible GCStrategy for a GC which is using the statepoint lowering code. At the moment, this GCStrategy doesn't really do much - aside from actually generate correct stackmaps that is - but I went ahead and added a few extra correctness checks as proof of concept. It's mostly here to provide documentation on how to do one, and to provide a point for various optimization legality hooks I'd like to add going forward. (For context, see the TODOs in InstCombine around gc.relocate.)

Most of the validation logic added here as proof of concept will soon move in to the Verifier.  That move is dependent on http://reviews.llvm.org/D6811

There was discussion in the review thread about addrspace(1) being reserved for something.  I'm going to follow up on a seperate llvmdev thread.  If needed, I'll update all the code at once.

Note that I am deliberately not making a GCStrategy required to use gc.statepoints with this change. I want to give folks out of tree - including myself - a chance to migrate. In a week or two, I'll make having a GCStrategy be required for gc.statepoints. To this end, I added the gc tag to one of the test cases but not others.

Differential Revision: http://reviews.llvm.org/D6808



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225365 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/StatepointLowering.cpp

@@ -17,6 +17,7 @@
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
+#include "llvm/CodeGen/GCStrategy.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/StackMaps.h"
 #include "llvm/IR/CallingConv.h"
@@ -417,6 +418,39 @@ static void lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
   getIncomingStatepointGCValues(Bases, Ptrs, Relocations,
                                 Statepoint.getCallSite(), Builder);
 
+#ifndef NDEBUG
+  // Check that each of the gc pointer and bases we've gotten out of the
+  // safepoint is something the strategy thinks might be a pointer into the GC
+  // heap.  This is basically just here to help catch errors during statepoint
+  // insertion. TODO: This should actually be in the Verifier, but we can't get
+  // to the GCStrategy from there (yet).
+  if (Builder.GFI) {
+    GCStrategy &S = Builder.GFI->getStrategy();
+    for (const Value *V : Bases) {
+      auto Opt = S.isGCManagedPointer(V);
+      if (Opt.hasValue()) {
+        assert(Opt.getValue() &&
+               "non gc managed base pointer found in statepoint");
+      }
+    }
+    for (const Value *V : Ptrs) {
+      auto Opt = S.isGCManagedPointer(V);
+      if (Opt.hasValue()) {
+        assert(Opt.getValue() &&
+               "non gc managed derived pointer found in statepoint");
+      }
+    }
+    for (const Value *V : Relocations) {
+      auto Opt = S.isGCManagedPointer(V);
+      if (Opt.hasValue()) {
+        assert(Opt.getValue() && "non gc managed pointer relocated");
+      }
+    }
+  }
+#endif
+
+
+
   // Before we actually start lowering (and allocating spill slots for values),
   // reserve any stack slots which we judge to be profitable to reuse for a
   // particular value.  This is purely an optimization over the code below and
@@ -498,6 +532,15 @@ void SelectionDAGBuilder::visitStatepoint(const CallInst &CI) {
   // This should catch any IR level mistake that's made when constructing or
   // transforming statepoints.
   ISP.verify();
+
+  // Check that the associated GCStrategy expects to encounter statepoints.
+  // TODO: This if should become an assert.  For now, we allow the GCStrategy
+  // to be optional for backwards compatibility.  This will only last a short
+  // period (i.e. a couple of weeks).
+  if (GFI) {
+    assert(GFI->getStrategy().useStatepoints() &&
+           "GCStrategy does not expect to encounter statepoints");
+  }
 #endif