[BOLT] Remove mutable from BB::LayoutIndex (#93224)

Removed mutability from BB::LayoutIndex, subsequently removed const from
BB::SetLayout, and changed BF::dfs to track visited blocks with a set as
opposed to tracking and altering LayoutIndexes for more consistent code.

Author: shawbyoung

bolt/include/bolt/Core/BinaryBasicBlock.h

@@ -115,7 +115,7 @@ class BinaryBasicBlock {
   unsigned Index{InvalidIndex};
 
   /// Index in the current layout.
-  mutable unsigned LayoutIndex{InvalidIndex};
+  unsigned LayoutIndex{InvalidIndex};
 
   /// Number of pseudo instructions in this block.
   uint32_t NumPseudos{0};
@@ -891,7 +891,7 @@ class BinaryBasicBlock {
   }
 
   /// Set layout index. To be used by BinaryFunction.
-  void setLayoutIndex(unsigned Index) const { LayoutIndex = Index; }
+  void setLayoutIndex(unsigned Index) { LayoutIndex = Index; }
 
   /// Needed by graph traits.
   BinaryFunction *getParent() const { return getFunction(); }

bolt/lib/Core/BinaryFunction.cpp

@@ -3641,8 +3641,8 @@ bool BinaryFunction::forEachEntryPoint(EntryPointCallbackTy Callback) const {
 
 BinaryFunction::BasicBlockListType BinaryFunction::dfs() const {
   BasicBlockListType DFS;
-  unsigned Index = 0;
   std::stack<BinaryBasicBlock *> Stack;
+  std::set<BinaryBasicBlock *> Visited;
 
   // Push entry points to the stack in reverse order.
   //
@@ -3659,17 +3659,13 @@ BinaryFunction::BasicBlockListType BinaryFunction::dfs() const {
   for (BinaryBasicBlock *const BB : reverse(EntryPoints))
     Stack.push(BB);
 
-  for (BinaryBasicBlock &BB : blocks())
-    BB.setLayoutIndex(BinaryBasicBlock::InvalidIndex);
-
   while (!Stack.empty()) {
     BinaryBasicBlock *BB = Stack.top();
     Stack.pop();
 
-    if (BB->getLayoutIndex() != BinaryBasicBlock::InvalidIndex)
+    if (Visited.find(BB) != Visited.end())
       continue;
-
-    BB->setLayoutIndex(Index++);
+    Visited.insert(BB);
     DFS.push_back(BB);
 
     for (BinaryBasicBlock *SuccBB : BB->landing_pads()) {

bolt/lib/Passes/IdenticalCodeFolding.cpp

@@ -356,7 +356,10 @@ Error IdenticalCodeFolding::runOnFunctions(BinaryContext &BC) {
                                         "ICF breakdown", opts::TimeICF);
     ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
       // Make sure indices are in-order.
-      BF.getLayout().updateLayoutIndices();
+      if (opts::ICFUseDFS)
+        BF.getLayout().updateLayoutIndices(BF.dfs());
+      else
+        BF.getLayout().updateLayoutIndices();
 
       // Pre-compute hash before pushing into hashtable.
       // Hash instruction operands to minimize hash collisions.

bolt/lib/Profile/YAMLProfileWriter.cpp

@@ -74,6 +74,9 @@ YAMLProfileWriter::convert(const BinaryFunction &BF, bool UseDFS,
   llvm::copy(UseDFS ? BF.dfs() : BF.getLayout().blocks(),
              std::back_inserter(Order));
 
+  const FunctionLayout Layout = BF.getLayout();
+  Layout.updateLayoutIndices(Order);
+
   for (const BinaryBasicBlock *BB : Order) {
     yaml::bolt::BinaryBasicBlockProfile YamlBB;
     YamlBB.Index = BB->getLayoutIndex();