From 69ee62cef82eef7d23d2c71fb133ba80cac18339 Mon Sep 17 00:00:00 2001
From: Vedant Kumar <vsk@apple.com>
Date: Fri, 29 Jun 2018 20:13:13 +0000
Subject: [PATCH] [LLVMContext] Detecting leaked instructions with metadata
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When instructions with metadata are accidentally leaked, the result is a
difficult-to-find memory corruption in ~LLVMContextImpl that leads to
random crashes.

Patch by Arvīds Kokins!

llvm-svn: 336010
---
 llvm/lib/IR/LLVMContextImpl.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/llvm/lib/IR/LLVMContextImpl.cpp b/llvm/lib/IR/LLVMContextImpl.cpp
index f0ac458..3c34ca5 100644
--- a/llvm/lib/IR/LLVMContextImpl.cpp
+++ b/llvm/lib/IR/LLVMContextImpl.cpp
@@ -48,6 +48,14 @@ LLVMContextImpl::~LLVMContextImpl() {
   while (!OwnedModules.empty())
     delete *OwnedModules.begin();
 
+#ifndef NDEBUG
+  // Check for metadata references from leaked Instructions.
+  for (auto &Pair : InstructionMetadata)
+    Pair.first->dump();
+  assert(InstructionMetadata.empty() &&
+         "Instructions with metadata have been leaked");
+#endif
+
   // Drop references for MDNodes.  Do this before Values get deleted to avoid
   // unnecessary RAUW when nodes are still unresolved.
   for (auto *I : DistinctMDNodes)
-- 
2.7.4