From 19ad3dd913c285778bc7e9746c063975fe42607c Mon Sep 17 00:00:00 2001
From: William Moses <gh@wsmoses.com>
Date: Sat, 29 Jan 2022 02:11:38 -0500
Subject: [PATCH] Custom error for unknown shadow (#456)

---
 enzyme/Enzyme/GradientUtils.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/enzyme/Enzyme/GradientUtils.cpp b/enzyme/Enzyme/GradientUtils.cpp
index 69dd5496809ca..35dc931429a58 100644
--- a/enzyme/Enzyme/GradientUtils.cpp
+++ b/enzyme/Enzyme/GradientUtils.cpp
@@ -94,6 +94,7 @@ llvm::cl::opt<bool> EnzymeFreeInternalAllocations(
     "enzyme-free-internal-allocations", cl::init(true), cl::Hidden,
     cl::desc("Always free internal allocations (disable if allocation needs "
              "access outside)"));
+extern void (*CustomErrorHandler)(const char *);
 }
 
 Value *GradientUtils::unwrapM(Value *const val, IRBuilder<> &BuilderM,
@@ -3417,6 +3418,13 @@ end:;
   assert(BuilderM.GetInsertBlock()->getParent());
   assert(oval);
 
+  if (CustomErrorHandler && isa<Constant>(oval)) {
+    std::string str;
+    raw_string_ostream ss(str);
+    ss << "cannot find shadow for " << *oval;
+    CustomErrorHandler(str.c_str());
+  }
+
   llvm::errs() << *newFunc->getParent() << "\n";
   llvm::errs() << "fn:" << *newFunc << "\noval=" << *oval
                << " icv=" << isConstantValue(oval) << "\n";