[llvm] [Attributor] Prevent infinite loop in AAGlobalValueInfoFloating (PR #94941)

[Ethan Luis McDonough via llvm-commits]

https://github.com/EthanLuisMcDonough created https://github.com/llvm/llvm-project/pull/94941

Global variables that reference themselves alongside a function that is called indirectly can cause an infinite loop in `AAGlobalValueInfoFloating`. The recursive reference is continually pushed back into the workload, causing the attributor to hang indefinitely. This patch fixes the issue by preventing the attributor from following a previously visited use.

>From c8655724bdf26aaac8a39d5fcf05bc1cfbab64a3 Mon Sep 17 00:00:00 2001
From: Ethan Luis McDonough <ethanluismcdonough at gmail.com>
Date: Mon, 10 Jun 2024 03:38:46 -0500
Subject: [PATCH] Fix infinite loop in attributor for recursive globals

---
 .../Transforms/IPO/AttributorAttributes.cpp   |  2 +-
 .../Attributor/recursive_globals.ll           | 24 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/Attributor/recursive_globals.ll

diff --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index 549d03645f939..8c268e3faf177 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -12031,7 +12031,7 @@ struct AAGlobalValueInfoFloating : public AAGlobalValueInfo {
                 SmallVectorImpl<const Value *> &Worklist) {
     Instruction *UInst = dyn_cast<Instruction>(U.getUser());
     if (!UInst) {
-      Follow = true;
+      Follow = !Uses.contains(&U);
       return true;
     }
 
diff --git a/llvm/test/Transforms/Attributor/recursive_globals.ll b/llvm/test/Transforms/Attributor/recursive_globals.ll
new file mode 100644
index 0000000000000..1af6383b063f4
--- /dev/null
+++ b/llvm/test/Transforms/Attributor/recursive_globals.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -passes=attributor
+
+ at glob1 = global { ptr, ptr } { ptr @glob1, ptr @fnc1 }
+ at glob2 = global { ptr, ptr } { ptr @glob3, ptr @fnc2 }
+ at glob3 = global { ptr, ptr } { ptr @glob2, ptr @fnc2 }
+
+define internal void @fnc1() {
+  ret void
+}
+
+define internal void @fnc2() {
+  ret void
+}
+
+define internal void @indr_caller(ptr %0) {
+  call void %0()
+  ret void
+}
+
+define void @main() {
+  call void @indr_caller(ptr @fnc1)
+  call void @indr_caller(ptr @fnc2)
+  ret void
+}