diff --git a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
--- a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -142,6 +142,14 @@
   /// Map generic virtual registers to their low-level type.
   VRegToTypeMap VRegToType;
 
+  /// Map a physical register into the virtual register it currently represents.
+  /// Useful for some target-hooks during the RegAllocFast to map a physical
+  /// register back to its virtual register. For instance, AMDGPU needs this
+  /// mapping inside the target spill hooks to identify the spills for certain
+  /// machine operands. This field is relevant only during RegAllocFast and will
+  /// be cleared elsewhere.
+  Register PhysToCurrentVirtReg;
+
   /// Keep track of the physical registers that are live in to the function.
   /// Live in values are typically arguments in registers.  LiveIn values are
   /// allowed to have virtual registers associated with them, stored in the
@@ -769,6 +777,9 @@
   /// type \p Ty.
   Register createGenericVirtualRegister(LLT Ty, StringRef Name = "");
 
+  void setPhysToCurrentVirtReg(Register Reg) { PhysToCurrentVirtReg = Reg; }
+  Register getPhysToCurrentVirtReg() const { return PhysToCurrentVirtReg; }
+
   /// Remove all types associated to virtual registers (after instruction
   /// selection and constraining of all generic virtual registers).
   void clearVirtRegTypes();
diff --git a/llvm/lib/CodeGen/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -707,6 +707,7 @@
   assert(PhysReg != 0 && "Trying to assign no register");
   LR.PhysReg = PhysReg;
   setPhysRegState(PhysReg, VirtReg);
+  MRI->setPhysToCurrentVirtReg(VirtReg);
 
   assignDanglingDebugValues(AtMI, VirtReg, PhysReg);
 }
@@ -1600,6 +1601,9 @@
     MRI->clearVirtRegs();
   }
 
+  // Clear PhysToCurrentVirtReg.
+  MRI->setPhysToCurrentVirtReg(Register());
+
   StackSlotForVirtReg.clear();
   LiveDbgValueMap.clear();
   return true;