Index: src/ResolvExpr/TypeEnvironment.h
===================================================================
--- src/ResolvExpr/TypeEnvironment.h	(revision 6f326b18619413c184048ffa17183130ed64766d)
+++ src/ResolvExpr/TypeEnvironment.h	(revision bd6e22644a77d8a4449c43eab3ff6b5a4e99d720)
@@ -37,4 +37,13 @@
 	//
 	// I've seen a TU go from 54 minutes to 1 minute 34 seconds with the addition of this comparator.
+	//
+	// Note: since this compares pointers for position, minor changes in the source file that affect
+	// memory layout can alter compilation time in unpredictable ways. For example, the placement
+	// of a line directive can reorder type pointers with respect to each other so that assertions
+	// are seen in different orders, causing a potentially different number of unification calls when
+	// resolving assertions. I've seen a TU go from 36 seconds to 27 seconds by reordering line directives
+	// alone, so it would be nice to fix this comparison so that assertions compare more consistently.
+	// I've tried to modify this to compare on mangle name instead of type as the second comparator, but
+	// this causes some assertions to never be recorded. More investigation is needed.
 	struct AssertCompare {
 		bool operator()( DeclarationWithType * d1, DeclarationWithType * d2 ) const {