[llvm] [MachineSink] Only add sink candidate if toBB is a successor of fromBB (PR #98540)

[via llvm-commits]

https://github.com/yozhu created https://github.com/llvm/llvm-project/pull/98540

Fix an issue in #97618 - only sink candidate from immediate predecessor block should be added as candidate for critical edge splitting.

>From c230c574fc3c7f3ebd837cf04a8a3aba2abf67db Mon Sep 17 00:00:00 2001
From: YongKang Zhu <yongzhu at fb.com>
Date: Thu, 11 Jul 2024 13:17:43 -0700
Subject: [PATCH] [MachineSink] Only add sink candidate if toBB is a successor
 of fromBB

---
 llvm/lib/CodeGen/MachineSink.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index bbc5ab13a0cd3..4d8de6765273f 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -913,7 +913,7 @@ bool MachineSinking::isWorthBreakingCriticalEdge(
     auto Res = CEMergeCandidates.try_emplace(Key, From);
     // We wanted to sink the same register into the same block, consider it to
     // be profitable.
-    if (!Res.second) {
+    if (!Res.second && Res.first->second->isSuccessor(To)) {
       // Return the source block that was previously held off.
       DeferredFromBlock = Res.first->second;
       return true;