ARM: support TLS accesses on Darwin platforms

Darwin TLS accesses most closely resemble ELF's general-dynamic situation,
since they have to be able to handle all possible situations. The descriptors
and so on are obviously slightly different though.

llvm-svn: 257039

1 files changed, 70 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 9cfb06b00c4..d49f46004d1 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2530,6 +2530,72 @@ SDValue ARMTargetLowering::LowerBlockAddress(SDValue Op,
   return DAG.getNode(ARMISD::PIC_ADD, DL, PtrVT, Result, PICLabel);
 }
 
+/// \brief Convert a TLS address reference into the correct sequence of loads
+/// and calls to compute the variable's address for Darwin, and return an
+/// SDValue containing the final node.
+
+/// Darwin only has one TLS scheme which must be capable of dealing with the
+/// fully general situation, in the worst case. This means:
+///     + "extern __thread" declaration.
+///     + Defined in a possibly unknown dynamic library.
+///
+/// The general system is that each __thread variable has a [3 x i32] descriptor
+/// which contains information used by the runtime to calculate the address. The
+/// only part of this the compiler needs to know about is the first word, which
+/// contains a function pointer that must be called with the address of the
+/// entire descriptor in "r0".
+///
+/// Since this descriptor may be in a different unit, in general access must
+/// proceed along the usual ARM rules. A common sequence to produce is:
+///
+///     movw rT1, :lower16:_var$non_lazy_ptr
+///     movt rT1, :upper16:_var$non_lazy_ptr
+///     ldr r0, [rT1]
+///     ldr rT2, [r0]
+///     blx rT2
+///     [...address now in r0...]
+SDValue
+ARMTargetLowering::LowerGlobalTLSAddressDarwin(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  assert(Subtarget->isTargetDarwin() && "TLS only supported on Darwin");
+  SDLoc DL(Op);
+
+  // First step is to get the address of the actua global symbol. This is where
+  // the TLS descriptor lives.
+  SDValue DescAddr = LowerGlobalAddressDarwin(Op, DAG);
+
+  // The first entry in the descriptor is a function pointer that we must call
+  // to obtain the address of the variable.
+  SDValue Chain = DAG.getEntryNode();
+  SDValue FuncTLVGet =
+      DAG.getLoad(MVT::i32, DL, Chain, DescAddr,
+                  MachinePointerInfo::getGOT(DAG.getMachineFunction()),
+                  false, true, true, 4);
+  Chain = FuncTLVGet.getValue(1);
+
+  MachineFunction &F = DAG.getMachineFunction();
+  MachineFrameInfo *MFI = F.getFrameInfo();
+  MFI->setAdjustsStack(true);
+
+  // TLS calls preserve all registers except those that absolutely must be
+  // trashed: R0 (it takes an argument), LR (it's a call) and CPSR (let's not be
+  // silly).
+  auto TRI =
+      getTargetMachine().getSubtargetImpl(*F.getFunction())->getRegisterInfo();
+  auto ARI = static_cast<const ARMRegisterInfo *>(TRI);
+  const uint32_t *Mask = ARI->getTLSCallPreservedMask(DAG.getMachineFunction());
+
+  // Finally, we can make the call. This is just a degenerate version of a
+  // normal AArch64 call node: r0 takes the address of the descriptor, and
+  // returns the address of the variable in this thread.
+  Chain = DAG.getCopyToReg(Chain, DL, ARM::R0, DescAddr, SDValue());
+  Chain =
+      DAG.getNode(ARMISD::CALL, DL, DAG.getVTList(MVT::Other, MVT::Glue),
+                  Chain, FuncTLVGet, DAG.getRegister(ARM::R0, MVT::i32),
+                  DAG.getRegisterMask(Mask), Chain.getValue(1));
+  return DAG.getCopyFromReg(Chain, DL, ARM::R0, MVT::i32, Chain.getValue(1));
+}
+
 // Lower ISD::GlobalTLSAddress using the "general dynamic" model
 SDValue
 ARMTargetLowering::LowerToTLSGeneralDynamicModel(GlobalAddressSDNode *GA,
@@ -2631,9 +2697,11 @@ ARMTargetLowering::LowerToTLSExecModels(GlobalAddressSDNode *GA,
 
 SDValue
 ARMTargetLowering::LowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const {
+  if (Subtarget->isTargetDarwin())
+    return LowerGlobalTLSAddressDarwin(Op, DAG);
+
   // TODO: implement the "local dynamic" model
-  assert(Subtarget->isTargetELF() &&
-         "TLS not implemented for non-ELF targets");
+  assert(Subtarget->isTargetELF() && "Only ELF implemented here");
   GlobalAddressSDNode *GA = cast<GlobalAddressSDNode>(Op);
   if (DAG.getTarget().Options.EmulatedTLS)
     return LowerToTLSEmulatedModel(GA, DAG);