1 files changed, 19 insertions, 9 deletions
diff --git a/lib/Target/AVR/AVRFrameLowering.cpp b/lib/Target/AVR/AVRFrameLowering.cpp
index ab42a7aa99011..25232d2e47e13 100644
--- a/lib/Target/AVR/AVRFrameLowering.cpp
+++ b/lib/Target/AVR/AVRFrameLowering.cpp
@@ -57,6 +57,7 @@ void AVRFrameLowering::emitPrologue(MachineFunction &MF,
   DebugLoc DL = (MBBI != MBB.end()) ? MBBI->getDebugLoc() : DebugLoc();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
   const AVRInstrInfo &TII = *STI.getInstrInfo();
+  bool HasFP = hasFP(MF);
 
   // Interrupt handlers re-enable interrupts in function entry.
   if (CallConv == CallingConv::AVR_INTR) {
@@ -65,6 +66,13 @@ void AVRFrameLowering::emitPrologue(MachineFunction &MF,
         .setMIFlag(MachineInstr::FrameSetup);
   }
 
+  // Save the frame pointer if we have one.
+  if (HasFP) {
+    BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
+        .addReg(AVR::R29R28, RegState::Kill)
+        .setMIFlag(MachineInstr::FrameSetup);
+  }
+
   // Emit special prologue code to save R1, R0 and SREG in interrupt/signal
   // handlers before saving any other registers.
   if (CallConv == CallingConv::AVR_INTR ||
@@ -72,6 +80,7 @@ void AVRFrameLowering::emitPrologue(MachineFunction &MF,
     BuildMI(MBB, MBBI, DL, TII.get(AVR::PUSHWRr))
         .addReg(AVR::R1R0, RegState::Kill)
         .setMIFlag(MachineInstr::FrameSetup);
+
     BuildMI(MBB, MBBI, DL, TII.get(AVR::INRdA), AVR::R0)
         .addImm(0x3f)
         .setMIFlag(MachineInstr::FrameSetup);
@@ -86,7 +95,7 @@ void AVRFrameLowering::emitPrologue(MachineFunction &MF,
   }
 
   // Early exit if the frame pointer is not needed in this function.
-  if (!hasFP(MF)) {
+  if (!HasFP) {
     return;
   }
 
@@ -165,6 +174,9 @@ void AVRFrameLowering::emitEpilogue(MachineFunction &MF,
     BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R1R0);
   }
 
+  if (hasFP(MF))
+    BuildMI(MBB, MBBI, DL, TII.get(AVR::POPWRd), AVR::R29R28);
+
   // Early exit if there is no need to restore the frame pointer.
   if (!FrameSize) {
     return;
@@ -216,8 +228,9 @@ void AVRFrameLowering::emitEpilogue(MachineFunction &MF,
 bool AVRFrameLowering::hasFP(const MachineFunction &MF) const {
   const AVRMachineFunctionInfo *FuncInfo = MF.getInfo<AVRMachineFunctionInfo>();
 
-  return (FuncInfo->getHasSpills() || FuncInfo->getHasAllocas() ||
-          FuncInfo->getHasStackArgs());
+  // TODO: We do not always need a frame pointer.
+  // This can be optimised.
+  return true;
 }
 
 bool AVRFrameLowering::spillCalleeSavedRegisters(
@@ -407,12 +420,9 @@ void AVRFrameLowering::determineCalleeSaves(MachineFunction &MF,
                                             RegScavenger *RS) const {
   TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
 
-  // Spill register Y when it is used as the frame pointer.
-  if (hasFP(MF)) {
-    SavedRegs.set(AVR::R29R28);
-    SavedRegs.set(AVR::R29);
-    SavedRegs.set(AVR::R28);
-  }
+  // If we have a frame pointer, the Y register needs to be saved as well.
+  // We don't do that here however - the prologue and epilogue generation
+  // code will handle it specially.
 }
 /// The frame analyzer pass.
 ///