update comment in the interest of precision

Author: nikomatsakis

src/librustc_mir/dataflow/mod.rs

@@ -461,14 +461,18 @@ pub struct AllSets<E: Idx> {
     /// equal to bits_per_block / (mem::size_of::<Word> * 8), rounded up.
     words_per_block: usize,
 
-    /// 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: Bits<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: Bits<E>,
 
     /// For each block, bits valid on entry to the block.