[llvm] [CodeGen] Avoid repeated hash lookups (NFC) (PR #123160)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/123160

None

>From 1a4341d7369c8b69650e150e0327105af1375089 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Wed, 15 Jan 2025 09:12:10 -0800
Subject: [PATCH] [CodeGen] Avoid repeated hash lookups (NFC)

---
 llvm/lib/CodeGen/MachineCSE.cpp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index 0a547050e91a8a..728fd2f5f7cd4f 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -832,12 +832,11 @@ bool MachineCSEImpl::ProcessBlockPRE(MachineDominatorTree *DT,
     if (!isPRECandidate(&MI, PhysRefs))
       continue;
 
-    if (!PREMap.count(&MI)) {
-      PREMap[&MI] = MBB;
+    auto [It, Inserted] = PREMap.try_emplace(&MI, MBB);
+    if (Inserted)
       continue;
-    }
 
-    auto MBB1 = PREMap[&MI];
+    auto *MBB1 = It->second;
     assert(
         !DT->properlyDominates(MBB, MBB1) &&
         "MBB cannot properly dominate MBB1 while DFS through dominators tree!");