[CodeGen] Prefer static frame index for STATEPOINT liveness args

Summary:
If a given liveness arg of STATEPOINT is at a fixed frame index
(e.g. a function argument passed on stack), prefer to use this
fixed location even the address is also in a register. If we use
the register it will generate a spill, which is not necessary
since the fixed frame index can be directly recorded in the stack
map.

Patch by Cherry Zhang <cherryyz@google.com>.

Reviewers: thanm, niravd, reames

Reviewed By: reames

Subscribers: cherryyz, reames, anna, arphaman, llvm-commits

Differential Revision: https://reviews.llvm.org/D53889

llvm-svn: 347998

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
index 54cbd6859f7..90a1b350fc9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
@@ -522,7 +522,16 @@ lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
   // The vm state arguments are lowered in an opaque manner.  We do not know
   // what type of values are contained within.
   for (const Value *V : SI.DeoptState) {
-    SDValue Incoming = Builder.getValue(V);
+    SDValue Incoming;
+    // If this is a function argument at a static frame index, generate it as
+    // the frame index.
+    if (const Argument *Arg = dyn_cast<Argument>(V)) {
+      int FI = Builder.FuncInfo.getArgumentFrameIndex(Arg);
+      if (FI != INT_MAX)
+        Incoming = Builder.DAG.getFrameIndex(FI, Builder.getFrameIndexTy());
+    }
+    if (!Incoming.getNode())
+      Incoming = Builder.getValue(V);
     const bool LiveInValue = LiveInDeopt && !isGCValue(V);
     lowerIncomingStatepointValue(Incoming, LiveInValue, Ops, Builder);
   }