[DAG] Change isGCValue detection for statepoint lowering

[skatkov]

Summary

isGCValue should detect whether the deopt value is a GC pointer.
Currently it checks by finding the value in SI.Bases and SI.Ptrs.
However these data structures contain only those values which
have corresponding gc.relocate call. So we can miss GC value if it
does not have gc.relocate call (dead after the call).

Check GC strategy whether pointer is GC one or consider any pointer
to be GC one conservatively.

[reames]

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

486

Minor improvement:
if (V->getType()->isPtrOrPtrVectorTy()) {

if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty))
  return *IsManaged;

return true; // conservative
}

[skatkov]

Philip, thank you for your suggestion.

[reames]

LGTM

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

#endif
   // particular, if the callee spills callee preserved registers we may not
   // be able to find a value placed in that register during the call.  This is
   // fine for live-out, but not for live-through.  If we were willing to make
   // assumptions about the code generator producing the callee, we could
   // potentially allow live-through values in callee saved registers.
   const bool LiveInDeopt =
     SI.StatepointFlags & (uint64_t)StatepointFlags::DeoptLiveIn;
 
-  auto isGCValue =[&](const Value *V) {
-    return is_contained(SI.Ptrs, V) || is_contained(SI.Bases, V);
+  auto isGCValue = [&](const Value *V) {
+    auto *Ty = V->getType();
+    if (!Ty->isPtrOrPtrVectorTy())
+      return false;
+    if (auto *GFI = Builder.GFI)
+      if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty))
+        return *IsManaged;
+    return true; // conservative
   };
 
   // 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
   // doesn't change semantics at all.  It is important for performance that we
   // reserve slots for both deopt and gc values before lowering either.
   for (const Value *V : SI.DeoptState) {