[llvm] [CGSCC] Verify that call graph is valid after iteration (PR #94692)

[Arthur Eubanks via llvm-commits]

https://github.com/aeubanks created https://github.com/llvm/llvm-project/pull/94692

Only in expensive checks, to match other LazyCallGraph verification.

Is helpful for verifying LazyCallGraph updates. Many issues only surface when we reuse the LazyCallGraph.

>From a8eaa20116e0a26b8423c62fcb7f1319562d6f99 Mon Sep 17 00:00:00 2001
From: Arthur Eubanks <aeubanks at google.com>
Date: Thu, 6 Jun 2024 22:14:37 +0000
Subject: [PATCH] [CGSCC] Verify that call graph is valid after iteration

Only in expensive checks, to match other LazyCallGraph verification.

Is helpful for verifying LazyCallGraph updates. Many issues only surface when we reuse the LazyCallGraph.
---
 llvm/include/llvm/Analysis/LazyCallGraph.h | 5 +++++
 llvm/lib/Analysis/CGSCCPassManager.cpp     | 5 +++++
 llvm/lib/Analysis/LazyCallGraph.cpp        | 8 ++++++++
 3 files changed, 18 insertions(+)

diff --git a/llvm/include/llvm/Analysis/LazyCallGraph.h b/llvm/include/llvm/Analysis/LazyCallGraph.h
index 68c98b416ce96..ac8ca207d312b 100644
--- a/llvm/include/llvm/Analysis/LazyCallGraph.h
+++ b/llvm/include/llvm/Analysis/LazyCallGraph.h
@@ -943,6 +943,11 @@ class LazyCallGraph {
   LazyCallGraph(LazyCallGraph &&G);
   LazyCallGraph &operator=(LazyCallGraph &&RHS);
 
+#if !defined(NDEBUG) || defined(EXPENSIVE_CHECKS)
+  /// Verify that every RefSCC is valid.
+  void verify();
+#endif
+
   bool invalidate(Module &, const PreservedAnalyses &PA,
                   ModuleAnalysisManager::Invalidator &);
 
diff --git a/llvm/lib/Analysis/CGSCCPassManager.cpp b/llvm/lib/Analysis/CGSCCPassManager.cpp
index 2246887afe68a..8ae5c3dee6103 100644
--- a/llvm/lib/Analysis/CGSCCPassManager.cpp
+++ b/llvm/lib/Analysis/CGSCCPassManager.cpp
@@ -340,6 +340,11 @@ ModuleToPostOrderCGSCCPassAdaptor::run(Module &M, ModuleAnalysisManager &AM) {
     } while (!RCWorklist.empty());
   }
 
+#if defined(EXPENSIVE_CHECKS)
+  // Verify that the call graph is still valid.
+  CG.verify();
+#endif
+
   // By definition we preserve the call garph, all SCC analyses, and the
   // analysis proxies by handling them above and in any nested pass managers.
   PA.preserveSet<AllAnalysesOn<LazyCallGraph::SCC>>();
diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 1e5cf84d589b0..48a7ca0061600 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -211,6 +211,14 @@ LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
   updateGraphPtrs();
 }
 
+#if !defined(NDEBUG) || defined(EXPENSIVE_CHECKS)
+void LazyCallGraph::verify() {
+  for (RefSCC &RC : postorder_ref_sccs()) {
+    RC.verify();
+  }
+}
+#endif
+
 bool LazyCallGraph::invalidate(Module &, const PreservedAnalyses &PA,
                                ModuleAnalysisManager::Invalidator &) {
   // Check whether the analysis, all analyses on functions, or the function's