From 6e6ae6003e703f4ead5f2140303c93ccd4195f23 Mon Sep 17 00:00:00 2001
From: "Aman Khalid (from Dev Box)" <amankhalid@microsoft.com>
Date: Sun, 6 Apr 2025 16:38:49 -0400
Subject: [PATCH] Skip rarely-run block expansion during control flow opts

---
 src/coreclr/jit/optimizer.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/coreclr/jit/optimizer.cpp b/src/coreclr/jit/optimizer.cpp
index 10abc319b6184f..b96988cf086d71 100644
--- a/src/coreclr/jit/optimizer.cpp
+++ b/src/coreclr/jit/optimizer.cpp
@@ -2379,11 +2379,11 @@ PhaseStatus Compiler::optOptimizeFlow()
 
     bool modified = fgUpdateFlowGraph(/* doTailDuplication */ true);
 
-    // Skipping fgExpandRarelyRunBlocks when we have PGO data incurs diffs if the profile is inconsistent,
-    // as it will propagate missing profile weights throughout the flowgraph.
-    // Running profile synthesis beforehand should get rid of these diffs.
     // TODO: Always rely on profile synthesis to identify cold blocks.
-    modified |= fgExpandRarelyRunBlocks();
+    if (!fgIsUsingProfileWeights())
+    {
+        modified |= fgExpandRarelyRunBlocks();
+    }
 
     // Run branch optimizations for non-handler blocks.
     assert(!fgFuncletsCreated);