[llvm] [CodeGen] Avoid repeated map lookups (NFC) (PR #127025)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/127025

None

>From f44f1f08dd08e5734c9a00cb9f955c6be082e40e Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Wed, 12 Feb 2025 09:02:36 -0800
Subject: [PATCH] [CodeGen] Avoid repeated map lookups (NFC)

---
 llvm/lib/CodeGen/LiveStacks.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/CodeGen/LiveStacks.cpp b/llvm/lib/CodeGen/LiveStacks.cpp
index d615caf48c0ad..c07d985a09d1f 100644
--- a/llvm/lib/CodeGen/LiveStacks.cpp
+++ b/llvm/lib/CodeGen/LiveStacks.cpp
@@ -62,8 +62,8 @@ LiveStacks::getOrCreateInterval(int Slot, const TargetRegisterClass *RC) {
     S2RCMap.insert(std::make_pair(Slot, RC));
   } else {
     // Use the largest common subclass register class.
-    const TargetRegisterClass *OldRC = S2RCMap[Slot];
-    S2RCMap[Slot] = TRI->getCommonSubClass(OldRC, RC);
+    const TargetRegisterClass *&OldRC = S2RCMap[Slot];
+    OldRC = TRI->getCommonSubClass(OldRC, RC);
   }
   return I->second;
 }