Index: include/llvm/IR/Function.h
===================================================================
--- include/llvm/IR/Function.h
+++ include/llvm/IR/Function.h
@@ -158,7 +158,7 @@
   /// Returns the number of non-debug IR instructions in this function.
   /// This is equivalent to the sum of the sizes of each basic block contained
   /// within this function.
-  unsigned getInstructionCount();
+  unsigned getInstructionCount() const;
 
   /// Returns the FunctionType for me.
   FunctionType *getFunctionType() const {
Index: lib/IR/Function.cpp
===================================================================
--- lib/IR/Function.cpp
+++ lib/IR/Function.cpp
@@ -195,9 +195,9 @@
   return getType()->getContext();
 }
 
-unsigned Function::getInstructionCount() {
+unsigned Function::getInstructionCount() const {
   unsigned NumInstrs = 0;
-  for (BasicBlock &BB : BasicBlocks)
+  for (const BasicBlock &BB : BasicBlocks)
     NumInstrs += std::distance(BB.instructionsWithoutDebug().begin(),
                                BB.instructionsWithoutDebug().end());
   return NumInstrs;