Rollup merge of rust-lang#139886 - nnethercote:graphviz_borrowck, r=compiler-errors

`borrowck_graphviz_*` attribute tweaks

A couple of small fixes to out-of-date things.

r? `@davidtwco`

Author: Zalathar

compiler/rustc_mir_dataflow/src/framework/graphviz.rs

@@ -122,7 +122,7 @@ impl RustcMirAttrs {
                 })
             } else if attr.has_name(sym::borrowck_graphviz_format) {
                 Self::set_field(&mut ret.formatter, tcx, &attr, |s| match s {
-                    sym::gen_kill | sym::two_phase => Ok(s),
+                    sym::two_phase => Ok(s),
                     _ => {
                         tcx.dcx().emit_err(UnknownFormatter { span: attr.span() });
                         Err(())

compiler/rustc_span/src/symbol.rs

@@ -1068,7 +1068,6 @@ symbols! {
         ge,
         gen_blocks,
         gen_future,
-        gen_kill,
         generator_clone,
         generators,
         generic_arg_infer,

src/doc/rustc-dev-guide/src/compiler-debugging.md

@@ -301,7 +301,8 @@ Right below you can find elaborate explainers on a selected few.
 
 Some compiler options for debugging specific features yield graphviz graphs -
 e.g. the `#[rustc_mir(borrowck_graphviz_postflow="suffix.dot")]` attribute
-dumps various borrow-checker dataflow graphs.
+on a function dumps various borrow-checker dataflow graphs in conjunction with
+`-Zdump-mir-dataflow`.
 
 These all produce `.dot` files. To view these files, install graphviz (e.g.
 `apt-get install graphviz`) and then run the following commands:

tests/ui/mir-dataflow/README.md

@@ -42,12 +42,3 @@ each generated output path.
    on *entry* to each block, as well as the gen- and kill-sets that
    were so-called "transfer functions" summarizing the effect of each
    basic block.
-
- * (In addition to the `borrowck_graphviz_postflow` attribute-key
-   noted above, there is also `borrowck_graphviz_preflow`; it has the
-   same interface and generates the same set of files, but it renders
-   the dataflow state after building the gen- and kill-sets but
-   *before* running the dataflow analysis itself, so each entry-set is
-   just the initial default state for that dataflow analysis. This is
-   less useful for understanding the error message output in these
-   tests.)