[llvm] [memprof] Use const ref for IndexedRecord (PR #94114)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/94114

The type of *Iter here is "const IndexedMemProfRecord &" as defined in
RecordLookupTrait.  Assigning *Iter to a variable of type
"const IndexedMemProfRecord &" avoids a copy, reducing the cycle and
instruction counts by 1.8% and 0.2%, respectively, with
"llvm-profdata show" modified to deserialize all MemProfRecords.

Note that RecordLookupTrait has an internal copy of
IndexedMemProfRecord, so we don't have to worry about a dangling
reference to a temporary.

>From cb9c5f95a30fdf9cafbb5047b04368b98f703e42 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Sun, 26 May 2024 00:15:53 -0700
Subject: [PATCH] [memprof] Use const ref for IndexedRecord

The type of *Iter here is "const IndexedMemProfRecord &" as defined in
RecordLookupTrait.  Assigning *Iter to a variable of type
"const IndexedMemProfRecord &" avoids a copy, reducing the cycle and
instruction counts by 1.8% and 0.2%, respectively, with
"llvm-profdata show" modified to deserialize all MemProfRecords.

Note that RecordLookupTrait has an internal copy of
IndexedMemProfRecord, so we don't have to worry about a dangling
reference to a temporary.
---
 llvm/lib/ProfileData/InstrProfReader.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/ProfileData/InstrProfReader.cpp b/llvm/lib/ProfileData/InstrProfReader.cpp
index 1e66716294689..8298d3d372951 100644
--- a/llvm/lib/ProfileData/InstrProfReader.cpp
+++ b/llvm/lib/ProfileData/InstrProfReader.cpp
@@ -1613,7 +1613,7 @@ IndexedMemProfReader::getMemProfRecord(const uint64_t FuncNameHash) const {
         instrprof_error::unknown_function,
         "memprof record not found for function hash " + Twine(FuncNameHash));
 
-  const memprof::IndexedMemProfRecord IndexedRecord = *Iter;
+  const memprof::IndexedMemProfRecord &IndexedRecord = *Iter;
   switch (Version) {
   case memprof::Version0:
   case memprof::Version1: