[llvm] [LLVM][CanonicalizeFreezeInLoops] fix duplicate removal (PR #74716)

[Wei Tao via llvm-commits]

https://github.com/Friedrich20 created https://github.com/llvm/llvm-project/pull/74716

This PR fixes [#74572](https://github.com/llvm/llvm-project/issues/74572) where the the freeze instruction could be found twice by the pass CanonicalizeFreezeInLoops, and then the compiling may crash in second removal since the instruction has already gone.

>From 5ef11803b597fec44b64239824a4c9d3280cfea6 Mon Sep 17 00:00:00 2001
From: Wei Tao <friedrich.taow at gmail.com>
Date: Thu, 7 Dec 2023 21:33:40 +0800
Subject: [PATCH] [LLVM][CanonicalizeFreezeInLoops] fix duplicate removal

---
 .../Transforms/Utils/CanonicalizeFreezeInLoops.cpp  | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/CanonicalizeFreezeInLoops.cpp b/llvm/lib/Transforms/Utils/CanonicalizeFreezeInLoops.cpp
index fb4d828853772..ff1eb17e0c248 100644
--- a/llvm/lib/Transforms/Utils/CanonicalizeFreezeInLoops.cpp
+++ b/llvm/lib/Transforms/Utils/CanonicalizeFreezeInLoops.cpp
@@ -151,11 +151,18 @@ bool CanonicalizeFreezeInLoopsImpl::run() {
       }
     }
 
+    bool Exist = false;
     auto Visit = [&](User *U) {
       if (auto *FI = dyn_cast<FreezeInst>(U)) {
-        LLVM_DEBUG(dbgs() << "canonfr: found: " << *FI << "\n");
-        Info.FI = FI;
-        Candidates.push_back(Info);
+        for (const auto &Candidate : Candidates) {
+          auto *FI_cand = Candidate.FI;
+          Exist = (FI_cand == FI) ? true : Exist;
+        }
+        if (!Exist) {
+          LLVM_DEBUG(dbgs() << "canonfr: found: " << *FI << "\n");
+          Info.FI = FI;
+          Candidates.push_back(Info);
+        }
       }
     };
     for_each(PHI.users(), Visit);