Index: include/llvm/CodeGen/TargetSubtargetInfo.h
===================================================================
--- include/llvm/CodeGen/TargetSubtargetInfo.h
+++ include/llvm/CodeGen/TargetSubtargetInfo.h
@@ -248,6 +248,9 @@
   /// Returns string representation of scheduler comment
   std::string getSchedInfoStr(const MachineInstr &MI) const override;
   std::string getSchedInfoStr(MCInst const &MCI) const override;
+
+  /// This is called after a .mir file was loaded.
+  virtual void mirFileLoaded(MachineFunction &MF) const;
 };
 
 } // end namespace llvm
Index: lib/CodeGen/MIRParser/MIRParser.cpp
===================================================================
--- lib/CodeGen/MIRParser/MIRParser.cpp
+++ lib/CodeGen/MIRParser/MIRParser.cpp
@@ -417,6 +417,8 @@
 
   computeFunctionProperties(MF);
 
+  MF.getSubtarget().mirFileLoaded(MF);
+
   MF.verify();
   return false;
 }
Index: lib/CodeGen/TargetSubtargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetSubtargetInfo.cpp
+++ lib/CodeGen/TargetSubtargetInfo.cpp
@@ -111,3 +111,6 @@
       TSchedModel.computeInstrRThroughput(MCI.getOpcode());
   return createSchedInfoStr(Latency, RThroughput);
 }
+
+void TargetSubtargetInfo::mirFileLoaded(MachineFunction &MF) const {
+}
Index: lib/Target/AArch64/AArch64FrameLowering.cpp
===================================================================
--- lib/Target/AArch64/AArch64FrameLowering.cpp
+++ lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -190,11 +190,24 @@
   const MachineFrameInfo &MFI = MF.getFrameInfo();
   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
   // Retain behavior of always omitting the FP for leaf functions when possible.
-  return (MFI.hasCalls() &&
-          MF.getTarget().Options.DisableFramePointerElim(MF)) ||
-         MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
-         MFI.hasStackMap() || MFI.hasPatchPoint() ||
-         RegInfo->needsStackRealignment(MF);
+  if (MFI.hasCalls() && MF.getTarget().Options.DisableFramePointerElim(MF))
+    return true;
+  if (MFI.hasVarSizedObjects() || MFI.isFrameAddressTaken() ||
+      MFI.hasStackMap() || MFI.hasPatchPoint() ||
+      RegInfo->needsStackRealignment(MF))
+    return true;
+  // With large callframes around we may need to use FP to access the scavenging
+  // emergency spillslot.
+  //
+  // Unfortunately some calls to hasFP() like machine verifier ->
+  // getReservedReg() -> hasFP in the middle of global isel are too early
+  // to know the max call frame size. Hopefully conservatively returning "true"
+  // in those cases is fine.
+  // The number 255 is taken from estimateRSStackSizeLimit().
+  if (!MFI.isMaxCallFrameSizeComputed() || MFI.getMaxCallFrameSize() > 255)
+    return true;
+
+  return false;
 }
 
 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
@@ -1253,6 +1266,7 @@
       unsigned Size = TRI->getSpillSize(RC);
       unsigned Align = TRI->getSpillAlignment(RC);
       int FI = MFI.CreateStackObject(Size, Align, false);
+      MFI.setScavSlot(FI);
       RS->addScavengingFrameIndex(FI);
       DEBUG(dbgs() << "No available CS registers, allocated fi#" << FI
                    << " as the emergency spill slot.\n");
Index: lib/Target/AArch64/AArch64ISelLowering.h
===================================================================
--- lib/Target/AArch64/AArch64ISelLowering.h
+++ lib/Target/AArch64/AArch64ISelLowering.h
@@ -649,6 +649,8 @@
                           SelectionDAG &DAG) const override;
 
   bool shouldNormalizeToSelectSequence(LLVMContext &, EVT) const override;
+
+  void finalizeLowering(MachineFunction &MF) const override;
 };
 
 namespace AArch64 {
Index: lib/Target/AArch64/AArch64ISelLowering.cpp
===================================================================
--- lib/Target/AArch64/AArch64ISelLowering.cpp
+++ lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -10983,3 +10983,8 @@
 
   return 3 * getPointerTy(DL).getSizeInBits() + 2 * 32;
 }
+
+void AArch64TargetLowering::finalizeLowering(MachineFunction &MF) const {
+  MF.getFrameInfo().computeMaxCallFrameSize(MF);
+  TargetLoweringBase::finalizeLowering(MF);
+}
Index: lib/Target/AArch64/AArch64RegisterInfo.cpp
===================================================================
--- lib/Target/AArch64/AArch64RegisterInfo.cpp
+++ lib/Target/AArch64/AArch64RegisterInfo.cpp
@@ -225,11 +225,13 @@
 
 bool
 AArch64RegisterInfo::useFPForScavengingIndex(const MachineFunction &MF) const {
-  const MachineFrameInfo &MFI = MF.getFrameInfo();
-  // AArch64FrameLowering::resolveFrameIndexReference() can always fall back
-  // to the stack pointer, so only put the emergency spill slot next to the
-  // FP when there's no better way to access it (SP or base pointer).
-  return MFI.hasVarSizedObjects() && !hasBasePointer(MF);
+  // This function indicates whether the emergency spillslot should be placed
+  // close to the beginning of the stackframe (closer to FP) or the end
+  // (closer to SP).
+  //
+  // The beginning works most reliably if we have a frame pointer.
+  const AArch64FrameLowering &TFI = *getFrameLowering(MF);
+  return TFI.hasFP(MF);
 }
 
 bool AArch64RegisterInfo::requiresFrameIndexScavenging(
Index: lib/Target/AArch64/AArch64Subtarget.h
===================================================================
--- lib/Target/AArch64/AArch64Subtarget.h
+++ lib/Target/AArch64/AArch64Subtarget.h
@@ -328,6 +328,8 @@
       return false;
     }
   }
+
+  void mirFileLoaded(MachineFunction &MF) const override;
 };
 } // End llvm namespace
 
Index: lib/Target/AArch64/AArch64Subtarget.cpp
===================================================================
--- lib/Target/AArch64/AArch64Subtarget.cpp
+++ lib/Target/AArch64/AArch64Subtarget.cpp
@@ -267,3 +267,13 @@
 AArch64Subtarget::getCustomPBQPConstraints() const {
   return balanceFPOps() ? llvm::make_unique<A57ChainingConstraint>() : nullptr;
 }
+
+void AArch64Subtarget::mirFileLoaded(MachineFunction &MF) const {
+  // We usually compute max call frame size after ISel. Do the computation now
+  // if the .mir file didn't specify it. Note that this will probably give you
+  // bogus values after PEI has eliminated the callframe setup/destroy pseudo
+  // instructions, specify explicitely if you need it to be correct.
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  if (!MFI.isMaxCallFrameSizeComputed())
+    MFI.computeMaxCallFrameSize(MF);
+}