diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h
index ab29c4849ef..cc8385018d0 100644
--- a/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -603,6 +603,11 @@ public:
   /// (target independent) virtual register.
   unsigned getSize(unsigned VReg) const;
 
+  /// Set the size of \p VReg to \p Size.
+  /// Although the size should be set at build time, mir infrastructure
+  /// is not yet able to do it.
+  void setSize(unsigned VReg, unsigned Size);
+
   /// Create and return a new generic virtual register with a size of \p Size.
   /// \pre Size > 0.
   unsigned createGenericVirtualRegister(unsigned Size);
diff --git a/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp
index 2b81f6b2015..8521bee82e6 100644
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/lib/CodeGen/MachineRegisterInfo.cpp
@@ -109,6 +109,10 @@ MachineRegisterInfo::getSize(unsigned VReg) const {
   return SizeIt != getVRegToSize().end() ? SizeIt->second : 0;
 }
 
+void MachineRegisterInfo::setSize(unsigned VReg, unsigned Size) {
+  getVRegToSize()[VReg] = Size;
+}
+
 unsigned
 MachineRegisterInfo::createGenericVirtualRegister(unsigned Size) {
   assert(Size && "Cannot create empty virtual register");