[llvm] [MCA] use std::function instead of function_ref when storing (PR #91039)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/91039

This patch changes uses of llvm::function_ref for std::function when storing the callback inside of a class. The LLVM Programmer's manual mentions that llvm::function_ref is not safe to store as it contains pointers to external memory that are not guaranteed to exist in the future when it is stored.

This causes issues when setting callbacks inside of a class that manages MCA state. Passing a lambda directly to the set callback functions will end up causing UB/segfaults when the lambda is called as some external memory is now invalid. This is easy to work around (create a separate std::function, pass that into the function setting the callback), but isn't ideal.

>From 1a6fc0bcc3daa44fb897f23821c720e90976c390 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman at google.com>
Date: Sat, 4 May 2024 02:34:29 +0000
Subject: [PATCH] [MCA] use std::function instead of function_ref when storing

This patch changes uses of llvm::function_ref for std::function when
storing the callback inside of a class. The LLVM Programmer's manual
mentions that llvm::function_ref is not safe to store as it contains
pointers to external memory that are not guaranteed to exist in the
future when it is stored.

This causes issues when setting callbacks inside of a class that manages
MCA state. Passing a lambda directly to the set callback functions will
end up causing UB/segfaults when the lambda is called as some external
memory is now invalid. This is easy to work around (create a separate
std::function, pass that into the function setting the callback), but
isn't ideal.
---
 llvm/include/llvm/MCA/IncrementalSourceMgr.h | 2 +-
 llvm/include/llvm/MCA/InstrBuilder.h         | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/MCA/IncrementalSourceMgr.h b/llvm/include/llvm/MCA/IncrementalSourceMgr.h
index d53f1138b94059..81f9b51cf42f0c 100644
--- a/llvm/include/llvm/MCA/IncrementalSourceMgr.h
+++ b/llvm/include/llvm/MCA/IncrementalSourceMgr.h
@@ -41,7 +41,7 @@ class IncrementalSourceMgr : public SourceMgr {
   bool EOS = false;
 
   /// Called when an instruction is no longer needed.
-  using InstFreedCallback = llvm::function_ref<void(Instruction *)>;
+  using InstFreedCallback = std::function<void(Instruction *)>;
   InstFreedCallback InstFreedCB;
 
 public:
diff --git a/llvm/include/llvm/MCA/InstrBuilder.h b/llvm/include/llvm/MCA/InstrBuilder.h
index c8619af04b330f..35943724891487 100644
--- a/llvm/include/llvm/MCA/InstrBuilder.h
+++ b/llvm/include/llvm/MCA/InstrBuilder.h
@@ -79,8 +79,7 @@ class InstrBuilder {
   bool FirstCallInst;
   bool FirstReturnInst;
 
-  using InstRecycleCallback =
-      llvm::function_ref<Instruction *(const InstrDesc &)>;
+  using InstRecycleCallback = std::function<Instruction *(const InstrDesc &)>;
   InstRecycleCallback InstRecycleCB;
 
   Expected<const InstrDesc &>