[llvm] [SLPVectorizer] Avoid two successive hash lookups on the same key (PR #107143)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/107143

This patch replaces the find-try_emplace sequence with just one call
to try_emplace, thereby avoiding two successive hash lookups on the
same key.  I am not using the "inserted" boolean from try_emplace to
preserve the original behavior (that is, before PR 107123) that checks
to see if the value is nullptr or not.


>From 8a35528834f973fc79b53cf066168494e4eba5ca Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Tue, 3 Sep 2024 12:12:24 -0700
Subject: [PATCH] [SLPVectorizer] Avoid two successive hash lookups on the same
 key

This patch replaces the find-try_emplace sequence with just one call
to try_emplace, thereby avoiding two successive hash lookups on the
same key.  I am not using the "inserted" boolean from try_emplace to
preserve the original behavior (that is, before PR 107123) that checks
to see if the value is nullptr or not.
---
 llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 3b45ca11eb6f89..cf802034cd56a3 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -11804,10 +11804,9 @@ void BoUpSLP::reorderInputsAccordingToOpcode(ArrayRef<Value *> VL,
 }
 
 Instruction &BoUpSLP::getLastInstructionInBundle(const TreeEntry *E) {
-  auto It = EntryToLastInstruction.find(E);
-  if (It != EntryToLastInstruction.end())
-    return *It->second;
   auto &Res = EntryToLastInstruction.try_emplace(E).first->second;
+  if (Res)
+    return *Res;
   // Get the basic block this bundle is in. All instructions in the bundle
   // should be in this block (except for extractelement-like instructions with
   // constant indeces).