Add an informative comment.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123114 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/StrongPHIElimination.cpp b/lib/CodeGen/StrongPHIElimination.cpp
index 5c70423..94a86f2 100644
--- a/lib/CodeGen/StrongPHIElimination.cpp
+++ b/lib/CodeGen/StrongPHIElimination.cpp
@@ -89,7 +89,15 @@
/// Add a register in a new congruence class containing only itself.
void addReg(unsigned);
- /// Join the congruence classes of two registers.
+ /// Join the congruence classes of two registers. This function is biased
+ /// towards the left argument, i.e. after
+ ///
+ /// addReg(r2);
+ /// unionRegs(r1, r2);
+ ///
+ /// the leader of the unioned congruence class is the same as the leader of
+ /// r1's congruence class prior to the union. This is actually relied upon
+ /// in the copy insertion code.
void unionRegs(unsigned, unsigned);
/// Get the color of a register. The color is 0 if the register has been