Move BasicBlock::getTerminator definition to the header

This way it can be inlined to its caller. This method
shows up in the profile and it is essentially a fancy
getter. It would benefit from inlining into its callers.

NFC.

Author: arpilipe

llvm/include/llvm/IR/BasicBlock.h

@@ -116,7 +116,11 @@ class BasicBlock final : public Value, // Basic blocks are data objects also
 
   /// Returns the terminator instruction if the block is well formed or null
   /// if the block is not well formed.
-  const Instruction *getTerminator() const LLVM_READONLY;
+  const Instruction *getTerminator() const LLVM_READONLY {
+    if (InstList.empty() || !InstList.back().isTerminator())
+      return nullptr;
+    return &InstList.back();
+  }
   Instruction *getTerminator() {
     return const_cast<Instruction *>(
         static_cast<const BasicBlock *>(this)->getTerminator());

llvm/lib/IR/BasicBlock.cpp

@@ -148,12 +148,6 @@ const Module *BasicBlock::getModule() const {
   return getParent()->getParent();
 }
 
-const Instruction *BasicBlock::getTerminator() const {
-  if (InstList.empty() || !InstList.back().isTerminator())
-    return nullptr;
-  return &InstList.back();
-}
-
 const CallInst *BasicBlock::getTerminatingMustTailCall() const {
   if (InstList.empty())
     return nullptr;