[Statepoints] Let patchable statepoints have a symbolic call target.

Summary:
As added initially, statepoints required their call targets to be a
constant pointer null if ``numPatchBytes`` was non-zero.  This turns out
to be a problem ergonomically, since there is no way to mark patchable
statepoints as calling a (readable) symbolic value.

This change remove the restriction of requiring ``null`` call targets
for patchable statepoints, and changes PlaceSafepoints to maintain the
symbolic call target through its transformation.

Reviewers: reames, swaroop.sridhar

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11550

llvm-svn: 243502

3 files changed, 19 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
index 34688df4765..c62428d308e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
@@ -289,7 +289,23 @@ lowerCallFromStatepoint(ImmutableStatepoint ISP, MachineBasicBlock *LandingPad,
 
   ImmutableCallSite CS(ISP.getCallSite());
 
-  SDValue ActualCallee = Builder.getValue(ISP.getCalledValue());
+  SDValue ActualCallee;
+
+  if (ISP.getNumPatchBytes() > 0) {
+    // If we've been asked to emit a nop sequence instead of a call instruction
+    // for this statepoint then don't lower the call target, but use a constant
+    // `null` instead.  Not lowering the call target lets statepoint clients get
+    // away without providing a physical address for the symbolic call target at
+    // link time.
+
+    const auto &TLI = Builder.DAG.getTargetLoweringInfo();
+    const auto &DL = Builder.DAG.getDataLayout();
+
+    unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace();
+    ActualCallee = Builder.DAG.getConstant(0, Builder.getCurSDLoc(),
+                                           TLI.getPointerTy(DL, AS));
+  } else
+    ActualCallee = Builder.getValue(ISP.getCalledValue());
 
   assert(CS.getCallingConv() != CallingConv::AnyReg &&
          "anyregcc is not supported on statepoints!");
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 12e4f4ed056..2135dafef8d 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1544,12 +1544,6 @@ void Verifier::VerifyStatepoint(ImmutableCallSite CS) {
          "gc.statepoint callee must be of function pointer type", &CI, Target);
   FunctionType *TargetFuncType = cast<FunctionType>(PT->getElementType());
 
-  if (NumPatchBytes)
-    Assert(isa<ConstantPointerNull>(Target->stripPointerCasts()),
-           "gc.statepoint must have null as call target if number of patchable "
-           "bytes is non zero",
-           &CI);
-
   const Value *NumCallArgsV = CS.getArgument(3);
   Assert(isa<ConstantInt>(NumCallArgsV),
          "gc.statepoint number of arguments to underlying call "
diff --git a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
index 366301ad731..098e6eff15f 100644
--- a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
+++ b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
@@ -917,15 +917,10 @@ static Value *ReplaceWithStatepoint(const CallSite &CS, /* to replace */
       CS.getInstruction()->getContext(), AttributeSet::FunctionIndex,
       AttrsToRemove);
 
-  Value *StatepointTarget = NumPatchBytes == 0
-                                ? CS.getCalledValue()
-                                : ConstantPointerNull::get(cast<PointerType>(
-                                      CS.getCalledValue()->getType()));
-
   if (CS.isCall()) {
     CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
     CallInst *Call = Builder.CreateGCStatepointCall(
-        ID, NumPatchBytes, StatepointTarget,
+        ID, NumPatchBytes, CS.getCalledValue(),
         makeArrayRef(CS.arg_begin(), CS.arg_end()), None, None,
         "safepoint_token");
     Call->setTailCall(ToReplace->isTailCall());
@@ -951,7 +946,7 @@ static Value *ReplaceWithStatepoint(const CallSite &CS, /* to replace */
     // original block.
     Builder.SetInsertPoint(ToReplace->getParent());
     InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
-        ID, NumPatchBytes, StatepointTarget, ToReplace->getNormalDest(),
+        ID, NumPatchBytes, CS.getCalledValue(), ToReplace->getNormalDest(),
         ToReplace->getUnwindDest(), makeArrayRef(CS.arg_begin(), CS.arg_end()),
         None, None, "safepoint_token");