[SystemZ] Implement backchain attribute.

This introduces a SystemZ-specific "backchain" attribute on function, which
enables writing the frame backchain link as specified by the ABI.  This will
be used to implement -mbackchain option in clang.

Differential Revision: http://reviews.llvm.org/D19889

llvm-svn: 268571

2 files changed, 46 insertions, 4 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index 0bdfaf67c40..866e0db7c90 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -354,6 +354,15 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
 
   uint64_t StackSize = getAllocatedStackSize(MF);
   if (StackSize) {
+    // Determine if we want to store a backchain.
+    bool StoreBackchain = MF.getFunction()->hasFnAttribute("backchain");
+
+    // If we need backchain, save current stack pointer.  R1 is free at this
+    // point.
+    if (StoreBackchain)
+      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::LGR))
+        .addReg(SystemZ::R1D).addReg(SystemZ::R15D);
+
     // Allocate StackSize bytes.
     int64_t Delta = -int64_t(StackSize);
     emitIncrement(MBB, MBBI, DL, SystemZ::R15D, Delta, ZII);
@@ -364,6 +373,10 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF,
     BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
         .addCFIIndex(CFIIndex);
     SPOffsetFromCFA += Delta;
+
+    if (StoreBackchain)
+      BuildMI(MBB, MBBI, DL, ZII->get(SystemZ::STG))
+        .addReg(SystemZ::R1D).addReg(SystemZ::R15D).addImm(0).addReg(0);
   }
 
   if (HasFP) {
diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index c92aae8b8e7..09701951178 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -2835,8 +2835,9 @@ SDValue SystemZTargetLowering::lowerVACOPY(SDValue Op,
 SDValue SystemZTargetLowering::
 lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
   const TargetFrameLowering *TFI = Subtarget.getFrameLowering();
-  bool RealignOpt = !DAG.getMachineFunction().getFunction()->
-    hasFnAttribute("no-realign-stack");
+  MachineFunction &MF = DAG.getMachineFunction();
+  bool RealignOpt = !MF.getFunction()-> hasFnAttribute("no-realign-stack");
+  bool StoreBackchain = MF.getFunction()->hasFnAttribute("backchain");
 
   SDValue Chain = Op.getOperand(0);
   SDValue Size  = Op.getOperand(1);
@@ -2858,6 +2859,12 @@ lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
   // Get a reference to the stack pointer.
   SDValue OldSP = DAG.getCopyFromReg(Chain, DL, SPReg, MVT::i64);
 
+  // If we need a backchain, save it now.
+  SDValue Backchain;
+  if (StoreBackchain)
+    Backchain = DAG.getLoad(MVT::i64, DL, Chain, OldSP, MachinePointerInfo(),
+                            false, false, false, 0);
+
   // Add extra space for alignment if needed.
   if (ExtraAlignSpace)
     NeededSpace = DAG.getNode(ISD::ADD, DL, MVT::i64, NeededSpace,
@@ -2885,6 +2892,10 @@ lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
                   DAG.getConstant(~(RequiredAlign - 1), DL, MVT::i64));
   }
 
+  if (StoreBackchain)
+    Chain = DAG.getStore(Chain, DL, Backchain, NewSP, MachinePointerInfo(),
+                         false, false, 0);
+
   SDValue Ops[2] = { Result, Chain };
   return DAG.getMergeValues(Ops, DL);
 }
@@ -3336,8 +3347,26 @@ SDValue SystemZTargetLowering::lowerSTACKRESTORE(SDValue Op,
                                                  SelectionDAG &DAG) const {
   MachineFunction &MF = DAG.getMachineFunction();
   MF.getInfo<SystemZMachineFunctionInfo>()->setManipulatesSP(true);
-  return DAG.getCopyToReg(Op.getOperand(0), SDLoc(Op),
-                          SystemZ::R15D, Op.getOperand(1));
+  bool StoreBackchain = MF.getFunction()->hasFnAttribute("backchain");
+
+  SDValue Chain = Op.getOperand(0);
+  SDValue NewSP = Op.getOperand(1);
+  SDValue Backchain;
+  SDLoc DL(Op);
+
+  if (StoreBackchain) {
+    SDValue OldSP = DAG.getCopyFromReg(Chain, DL, SystemZ::R15D, MVT::i64);
+    Backchain = DAG.getLoad(MVT::i64, DL, Chain, OldSP, MachinePointerInfo(),
+                            false, false, false, 0);
+  }
+
+  Chain = DAG.getCopyToReg(Chain, DL, SystemZ::R15D, NewSP);
+
+  if (StoreBackchain)
+    Chain = DAG.getStore(Chain, DL, Backchain, NewSP, MachinePointerInfo(),
+                         false, false, 0);
+
+  return Chain;
 }
 
 SDValue SystemZTargetLowering::lowerPREFETCH(SDValue Op,