1 files changed, 7 insertions, 1 deletions
diff --git a/src/passes/MergeLocals.cpp b/src/passes/MergeLocals.cpp
index 9402e0669..b669c20d3 100644
--- a/src/passes/MergeLocals.cpp
+++ b/src/passes/MergeLocals.cpp
@@ -105,10 +105,16 @@ struct MergeLocals
     if (copies.empty()) {
       return;
     }
-    // compute all dependencies
     auto* func = getFunction();
+
+    // Compute the local graph. Note that we *cannot* do this lazily, as we want
+    // to read from the original state of the function while we are doing
+    // changes on it. That is, using an eager graph makes a snapshot of the
+    // initial state, which is what we want. If we can avoid that, this pass can
+    // be sped up by around 25%.
     LocalGraph preGraph(func, getModule());
     preGraph.computeSetInfluences();
+
     // optimize each copy
     std::unordered_map<LocalSet*, LocalSet*> optimizedToCopy,
       optimizedToTrivial;