[llvm] [Analysis] Avoid repeated hash lookups (NFC) (PR #128394)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata updated https://github.com/llvm/llvm-project/pull/128394

>From c725cd1f66807d294d31febc5544de30380db7eb Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Sat, 22 Feb 2025 02:27:51 -0800
Subject: [PATCH 1/2] [Analysis] Avoid repeated hash lookups (NFC)

---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index a1d91de3bb788..5988e40c56100 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1443,12 +1443,11 @@ void AccessAnalysis::processMemAccesses() {
                     UnderlyingObj->getType()->getPointerAddressSpace()))
               continue;
 
-            UnderlyingObjToAccessMap::iterator Prev =
-                ObjToLastAccess.find(UnderlyingObj);
-            if (Prev != ObjToLastAccess.end())
-              DepCands.unionSets(Access, Prev->second);
+            auto [It, Inserted] =
+                ObjToLastAccess.try_emplace(UnderlyingObj, Access);
+            if (!Inserted)
+              DepCands.unionSets(Access, It->second);
 
-            ObjToLastAccess[UnderlyingObj] = Access;
             LLVM_DEBUG(dbgs() << "  " << *UnderlyingObj << "\n");
           }
         }

>From 17929ccd0318e541e990e02f0861fdd3ea5ee176 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Sun, 23 Feb 2025 01:22:03 -0800
Subject: [PATCH 2/2] Update It->second even when the key-value pair is already
 present.

---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 5988e40c56100..cf3bb6a8eae1c 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1445,8 +1445,10 @@ void AccessAnalysis::processMemAccesses() {
 
             auto [It, Inserted] =
                 ObjToLastAccess.try_emplace(UnderlyingObj, Access);
-            if (!Inserted)
+            if (!Inserted) {
               DepCands.unionSets(Access, It->second);
+              It->second = Access;
+            }
 
             LLVM_DEBUG(dbgs() << "  " << *UnderlyingObj << "\n");
           }