3 files changed, 21 insertions, 1 deletions
diff --git a/src/ir/manipulation.h b/src/ir/manipulation.h
index 33c7d1bd7..64cd15dc3 100644
--- a/src/ir/manipulation.h
+++ b/src/ir/manipulation.h
@@ -64,6 +64,10 @@ inline OutputType* convert(InputType* input, MixedArena& allocator) {
   return output;
 }
 
+// Copy using a flexible custom copy function. This function is called on each
+// expression before copying it. If it returns a non-null value then that is
+// used (effectively overriding the normal copy), and if it is null then we do a
+// normal copy.
 using CustomCopier = std::function<Expression*(Expression*)>;
 Expression*
 flexibleCopy(Expression* original, Module& wasm, CustomCopier custom);
diff --git a/src/ir/module-utils.cpp b/src/ir/module-utils.cpp
index 5791ed77c..8ad127086 100644
--- a/src/ir/module-utils.cpp
+++ b/src/ir/module-utils.cpp
@@ -46,6 +46,15 @@ Function* copyFunction(Function* func,
                        Module& out,
                        Name newName,
                        std::optional<std::vector<Index>> fileIndexMap) {
+  auto ret = copyFunctionWithoutAdd(func, out, newName, fileIndexMap);
+  return out.addFunction(std::move(ret));
+}
+
+std::unique_ptr<Function>
+copyFunctionWithoutAdd(Function* func,
+                       Module& out,
+                       Name newName,
+                       std::optional<std::vector<Index>> fileIndexMap) {
   auto ret = std::make_unique<Function>();
   ret->name = newName.is() ? newName : func->name;
   ret->hasExplicitName = func->hasExplicitName;
@@ -71,7 +80,7 @@ Function* copyFunction(Function* func,
   ret->base = func->base;
   ret->noFullInline = func->noFullInline;
   ret->noPartialInline = func->noPartialInline;
-  return out.addFunction(std::move(ret));
+  return ret;
 }
 
 Global* copyGlobal(Global* global, Module& out) {
diff --git a/src/ir/module-utils.h b/src/ir/module-utils.h
index 0a101e5da..d9fd69428 100644
--- a/src/ir/module-utils.h
+++ b/src/ir/module-utils.h
@@ -33,6 +33,13 @@ copyFunction(Function* func,
              Name newName = Name(),
              std::optional<std::vector<Index>> fileIndexMap = std::nullopt);
 
+// As above, but does not add the copy to the module.
+std::unique_ptr<Function> copyFunctionWithoutAdd(
+  Function* func,
+  Module& out,
+  Name newName = Name(),
+  std::optional<std::vector<Index>> fileIndexMap = std::nullopt);
+
 Global* copyGlobal(Global* global, Module& out);
 
 Tag* copyTag(Tag* tag, Module& out);