From 7d4dc9f097d83c5ff12a8a64344dab9e6bd2e547 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Tue, 20 Sep 2022 20:14:11 -0700
Subject: [PATCH] JIT: improve scalability of optReachable

Use a bit vector to track the visited blocks. This scales much better than
using the per-block visited flags.

Fixes #44341.
---
 src/coreclr/jit/compiler.h              |  2 ++
 src/coreclr/jit/redundantbranchopts.cpp | 23 ++++++++++++-----------
 src/tests/issues.targets                |  3 ---
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/coreclr/jit/compiler.h b/src/coreclr/jit/compiler.h
index 3d284ecf96a27..8218b606194fb 100644
--- a/src/coreclr/jit/compiler.h
+++ b/src/coreclr/jit/compiler.h
@@ -6980,6 +6980,8 @@ class Compiler
     bool optRedundantBranch(BasicBlock* const block);
     bool optJumpThread(BasicBlock* const block, BasicBlock* const domBlock, bool domIsSameRelop);
     bool optReachable(BasicBlock* const fromBlock, BasicBlock* const toBlock, BasicBlock* const excludedBlock);
+    BitVecTraits* optReachableBitVecTraits;
+    BitVec        optReachableBitVec;
     void optRelopImpliesRelop(RelopImplicationInfo* rii);
 
     /**************************************************************************
diff --git a/src/coreclr/jit/redundantbranchopts.cpp b/src/coreclr/jit/redundantbranchopts.cpp
index 4b65d006af5d0..a333cad69aca7 100644
--- a/src/coreclr/jit/redundantbranchopts.cpp
+++ b/src/coreclr/jit/redundantbranchopts.cpp
@@ -74,16 +74,10 @@ PhaseStatus Compiler::optRedundantBranches()
         }
     };
 
+    optReachableBitVecTraits = nullptr;
     OptRedundantBranchesDomTreeVisitor visitor(this);
     visitor.WalkTree();
 
-    // Reset visited flags, in case we set any.
-    //
-    for (BasicBlock* const block : Blocks())
-    {
-        block->bbFlags &= ~BBF_VISITED;
-    }
-
 #if DEBUG
     if (verbose && visitor.madeChanges)
     {
@@ -1593,9 +1587,15 @@ bool Compiler::optReachable(BasicBlock* const fromBlock, BasicBlock* const toBlo
         return true;
     }
 
-    for (BasicBlock* const block : Blocks())
+    if (optReachableBitVecTraits == nullptr)
     {
-        block->bbFlags &= ~BBF_VISITED;
+        optReachableBitVecTraits = new (this, CMK_Reachability) BitVecTraits(fgBBNumMax + 1, this);
+        optReachableBitVec       = BitVecOps::MakeEmpty(optReachableBitVecTraits);
+    }
+    else
+    {
+        assert(BitVecTraits::GetSize(optReachableBitVecTraits) == fgBBNumMax + 1);
+        BitVecOps::ClearD(optReachableBitVecTraits, optReachableBitVec);
     }
 
     ArrayStack<BasicBlock*> stack(getAllocator(CMK_Reachability));
@@ -1604,7 +1604,6 @@ bool Compiler::optReachable(BasicBlock* const fromBlock, BasicBlock* const toBlo
     while (!stack.Empty())
     {
         BasicBlock* const nextBlock = stack.Pop();
-        nextBlock->bbFlags |= BBF_VISITED;
         assert(nextBlock != toBlock);
 
         if (nextBlock == excludedBlock)
@@ -1619,11 +1618,13 @@ bool Compiler::optReachable(BasicBlock* const fromBlock, BasicBlock* const toBlo
                 return true;
             }
 
-            if ((succ->bbFlags & BBF_VISITED) != 0)
+            if (BitVecOps::IsMember(optReachableBitVecTraits, optReachableBitVec, succ->bbNum))
             {
                 continue;
             }
 
+            BitVecOps::AddElemD(optReachableBitVecTraits, optReachableBitVec, succ->bbNum);
+
             stack.Push(succ);
         }
     }
diff --git a/src/tests/issues.targets b/src/tests/issues.targets
index 8653f6e609172..4d8386639b352 100644
--- a/src/tests/issues.targets
+++ b/src/tests/issues.targets
@@ -51,9 +51,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/readytorun/r2rdump/BasicTests/R2RDumpTest/*">
             <Issue>https://github.com/dotnet/runtime/issues/10888 https://github.com/dotnet/runtime/issues/11823 </Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/DevDiv_255294/DevDiv_255294/*">
-            <Issue>https://github.com/dotnet/runtime/issues/44341</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Directed/rvastatics/RVAOrderingTest/*">
             <Issue>https://github.com/dotnet/runtime/issues/55966</Issue>
         </ExcludeList>