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

[shaw young via llvm-commits]

https://github.com/shawbyoung created https://github.com/llvm/llvm-project/pull/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.


>From 4486b9c1a135fd1c758ac30379a133366fcd9917 Mon Sep 17 00:00:00 2001
From: shawbyoung <shawbyoung at gmail.com>
Date: Thu, 23 May 2024 10:58:35 -0700
Subject: [PATCH] [BOLT][NFC] Remove mutable from BB:LayoutIndex

---
 bolt/include/bolt/Core/BinaryBasicBlock.h |  4 ++--
 bolt/lib/Core/BinaryFunction.cpp          | 10 +++-------
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/bolt/include/bolt/Core/BinaryBasicBlock.h b/bolt/include/bolt/Core/BinaryBasicBlock.h
index bc95e2c4de3a1..a57b70714fe38 100644
--- a/bolt/include/bolt/Core/BinaryBasicBlock.h
+++ b/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(); }
diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index 10b93e702984f..51dc5a2cbf0d6 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -3636,8 +3636,8 @@ 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.
   //
@@ -3654,17 +3654,13 @@ 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()) {