[llvm] [SandboxVectorizer][NFCI] Fix use of possibly-uninitialized scalar. (PR #122201)

[Tyler Lanphear via llvm-commits]

https://github.com/tylanphear created https://github.com/llvm/llvm-project/pull/122201

The `EraseCallbackID` field is not always initialized in the ctor for SeedCollector; if not, it will be used uninitialized by its dtor. This could potentially lead to the erasure of a random callback, leading to a bug.

Fixed by initializing to a purposefully invalid ID (`std::numeric_limits<ContextID>::max()`)

>From 807217e0e987ca370b8892a3d9a03fe7e2ae184b Mon Sep 17 00:00:00 2001
From: Tyler Lanphear <tyler.lanphear at intel.com>
Date: Wed, 8 Jan 2025 17:14:09 -0800
Subject: [PATCH] [SandboxVectorizer][NFCI] Fix use of possibly-uninitialized
 scalar.

The `EraseCallbackID` field is not always initialized in the ctor for
SeedCollector, if not, it will be used uninitialized by its dtor. This
could potentially lead to the erasure of a random callback, leading to a
bug.

Fixed by initializing to a purposefully invalid ID
(`std::numeric_limits<ContextID>::max()`)
---
 .../Transforms/Vectorize/SandboxVectorizer/SeedCollector.h    | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h
index 6e16a84d832e5e..cc4ebb5c508414 100644
--- a/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h
+++ b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h
@@ -292,7 +292,9 @@ class SeedCollector {
   SeedContainer StoreSeeds;
   SeedContainer LoadSeeds;
   Context &Ctx;
-  Context::CallbackID EraseCallbackID;
+  Context::CallbackID EraseCallbackID =
+      std::numeric_limits<Context::CallbackID>::max();
+
   /// \Returns the number of SeedBundle groups for all seed types.
   /// This is to be used for limiting compilation time.
   unsigned totalNumSeedGroups() const {