Fix typos “an”→“a” and a few different ones that appeared in the same search

compiler/rustc_mir/src/interpret/validity.rs

@@ -857,7 +857,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                 // types above, in `visit_primitive`.
                 // In run-time mode, we accept pointers in here.  This is actually more
                 // permissive than a per-element check would be, e.g., we accept
-                // an &[u8] that contains a pointer even though bytewise checking would
+                // a &[u8] that contains a pointer even though bytewise checking would
                 // reject it.  However, that's good: We don't inherently want
                 // to reject those pointers, we just do not have the machinery to
                 // talk about parts of a pointer.

compiler/rustc_mir/src/transform/const_prop.rs

@@ -145,7 +145,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
 
         // FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
         // constants, instead of just checking for const-folding succeeding.
-        // That would require an uniform one-def no-mutation analysis
+        // That would require a uniform one-def no-mutation analysis
         // and RPO (or recursing when needing the value of a local).
         let mut optimization_finder = ConstPropagator::new(body, dummy_body, tcx);
         optimization_finder.visit_body(body);

compiler/rustc_mir/src/transform/rustc_peek.rs

@@ -92,7 +92,7 @@ impl<'tcx> MirPass<'tcx> for SanityCheck {
 /// "rustc_peek: bit not set".
 ///
 /// The intention is that one can write unit tests for dataflow by
-/// putting code into an UI test and using `rustc_peek` to
+/// putting code into a UI test and using `rustc_peek` to
 /// make observations about the results of dataflow static analyses.
 ///
 /// (If there are any calls to `rustc_peek` that do not match the