From f87687aa595399e578e60940e5fccae37c5cc114 Mon Sep 17 00:00:00 2001
From: Aman Khalid <amankhalid@microsoft.com>
Date: Mon, 21 Oct 2024 16:11:11 +0000
Subject: [PATCH] JIT: Use `BitVec` with `bbPostorderNum` key to track visited
 blocks during value numbering (#108943)

---
 src/coreclr/jit/compiler.h   |  2 +-
 src/coreclr/jit/valuenum.cpp | 19 ++++++++++---------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/coreclr/jit/compiler.h b/src/coreclr/jit/compiler.h
index 17926e2220b4d..be988a53b5767 100644
--- a/src/coreclr/jit/compiler.h
+++ b/src/coreclr/jit/compiler.h
@@ -5792,7 +5792,7 @@ class Compiler
     // Utility functions for fgValueNumber.
 
     // Value number a block or blocks in a loop
-    void fgValueNumberBlocks(BasicBlock* block, BlockSet& visitedBlocks);
+    void fgValueNumberBlocks(BasicBlock* block, BitVec& visitedBlocks, BitVecTraits* traits);
 
     // Perform value-numbering for the trees in "blk".
     void fgValueNumberBlock(BasicBlock* blk);
diff --git a/src/coreclr/jit/valuenum.cpp b/src/coreclr/jit/valuenum.cpp
index e48283d0ce68b..46bba8660d6ee 100644
--- a/src/coreclr/jit/valuenum.cpp
+++ b/src/coreclr/jit/valuenum.cpp
@@ -10888,14 +10888,14 @@ PhaseStatus Compiler::fgValueNumber()
     // Visiting that in reverse will ensure we visit a block's predecessors
     // before itself whenever possible.
     //
-    EnsureBasicBlockEpoch();
-    BlockSet     visitedBlocks(BlockSetOps::MakeEmpty(this));
+    BitVecTraits traits = m_dfsTree->PostOrderTraits();
+    BitVec       visitedBlocks(BitVecOps::MakeEmpty(&traits));
     BasicBlock** postOrder      = m_dfsTree->GetPostOrder();
     unsigned     postOrderCount = m_dfsTree->GetPostOrderCount();
     for (unsigned i = postOrderCount; i != 0; i--)
     {
         BasicBlock* const block = postOrder[i - 1];
-        fgValueNumberBlocks(block, visitedBlocks);
+        fgValueNumberBlocks(block, visitedBlocks, &traits);
     }
 
 #ifdef DEBUG
@@ -10912,8 +10912,9 @@ PhaseStatus Compiler::fgValueNumber()
 // fgValueNumberBlocks: Run value numbering for a block or blocks in a loop
 //
 // Arguments:
-//   block -- block to value number (may already have been numbered)
-//   visitedBlocks -- blocks that have already had VNs assigned
+//   block - block to value number (may already have been numbered)
+//   visitedBlocks - blocks that have already had VNs assigned
+//   traits - pointer to BitVecTraits describing visitedBlocks
 //
 // Notes:
 //
@@ -10922,11 +10923,11 @@ PhaseStatus Compiler::fgValueNumber()
 //   header, we switch to visiting the loop blocks in RPO, and once we finish
 //   that visitation, we try and refine loop header PHIs.
 //
-void Compiler::fgValueNumberBlocks(BasicBlock* block, BlockSet& visitedBlocks)
+void Compiler::fgValueNumberBlocks(BasicBlock* block, BitVec& visitedBlocks, BitVecTraits* traits)
 {
     // Because we're not following the strict RPO, we may have already visisted this block.
     //
-    if (BlockSetOps::IsMember(this, visitedBlocks, block->bbNum))
+    if (BitVecOps::IsMember(traits, visitedBlocks, block->bbPostorderNum))
     {
         return;
     }
@@ -10961,7 +10962,7 @@ void Compiler::fgValueNumberBlocks(BasicBlock* block, BlockSet& visitedBlocks)
 
     // Mark block as visited
     //
-    BlockSetOps::AddElemD(this, visitedBlocks, block->bbNum);
+    BitVecOps::AddElemD(traits, visitedBlocks, block->bbPostorderNum);
 
     // Is block the head of a loop?
     //
@@ -10971,7 +10972,7 @@ void Compiler::fgValueNumberBlocks(BasicBlock* block, BlockSet& visitedBlocks)
         // Yes. Visit all other loop blocks using the within-loop RPO.
         //
         loop->VisitLoopBlocksReversePostOrder([&](BasicBlock* block) {
-            fgValueNumberBlocks(block, visitedBlocks);
+            fgValueNumberBlocks(block, visitedBlocks, traits);
             return BasicBlockVisit::Continue;
         });