update comment in the interest of precision

Author: nikomatsakis

src/librustc_mir/dataflow/mod.rs

@@ -454,14 +454,18 @@ pub struct AllSets<E: Idx> {
     /// For each block, bits valid on entry to the block.
     on_entry_sets: Vec<IdxSet<E>>,
 
-    /// For each block, bits generated by executing the statements in
-    /// the block. (For comparison, the Terminator for each block is
-    /// handled in a flow-specific manner during propagation.)
+    /// For each block, bits generated by executing the statements +
+    /// terminator in the block -- with one caveat. In particular, for
+    /// *call terminators*, the effect of storing the destination is
+    /// not included, since that only takes effect on the **success**
+    /// edge (and not the unwind edge).
     gen_sets: Vec<HybridIdxSet<E>>,
 
-    /// For each block, bits killed by executing the statements in the
-    /// block. (For comparison, the Terminator for each block is
-    /// handled in a flow-specific manner during propagation.)
+    /// For each block, bits killed by executing the statements +
+    /// terminator in the block -- with one caveat. In particular, for
+    /// *call terminators*, the effect of storing the destination is
+    /// not included, since that only takes effect on the **success**
+    /// edge (and not the unwind edge).
     kill_sets: Vec<HybridIdxSet<E>>,
 }