[BOLT][NFC] Extend updateLayoutIndices (#93861)

Make FunctionLayout::updateLayoutIndices const and add an overloaded
function that updates LayoutIndices given an Order parameter.

Author: shawbyoung

bolt/include/bolt/Core/FunctionLayout.h

@@ -213,7 +213,8 @@ class FunctionLayout {
   void eraseBasicBlocks(const DenseSet<const BinaryBasicBlock *> ToErase);
 
   /// Make sure fragments' and basic blocks' indices match the current layout.
-  void updateLayoutIndices();
+  void updateLayoutIndices() const;
+  void updateLayoutIndices(ArrayRef<BinaryBasicBlock *> Order) const;
 
   /// Replace the current layout with NewLayout. Uses the block's
   /// self-identifying fragment number to assign blocks to infer function

bolt/lib/Core/FunctionLayout.cpp

@@ -164,15 +164,20 @@ void FunctionLayout::eraseBasicBlocks(
   updateLayoutIndices();
 }
 
-void FunctionLayout::updateLayoutIndices() {
+void FunctionLayout::updateLayoutIndices() const {
   unsigned BlockIndex = 0;
-  for (FunctionFragment &FF : fragments()) {
+  for (const FunctionFragment &FF : fragments()) {
     for (BinaryBasicBlock *const BB : FF) {
       BB->setLayoutIndex(BlockIndex++);
       BB->setFragmentNum(FF.getFragmentNum());
     }
   }
 }
+void FunctionLayout::updateLayoutIndices(
+    ArrayRef<BinaryBasicBlock *> Order) const {
+  for (auto [Index, BB] : llvm::enumerate(Order))
+    BB->setLayoutIndex(Index);
+}
 
 bool FunctionLayout::update(const ArrayRef<BinaryBasicBlock *> NewLayout) {
   const bool EqualBlockOrder = llvm::equal(Blocks, NewLayout);