unpretty=thir-tree: don't require the final expr to be the entrypoint

Author: dianne

compiler/rustc_mir_build/src/builder/mod.rs

@@ -451,10 +451,6 @@ fn construct_fn<'tcx>(
 let span = tcx.def_span(fn_def);
 let fn_id = tcx.local_def_id_to_hir_id(fn_def);
 
-// The representation of thir for `-Zunpretty=thir-tree` relies on
-// the entry expression being the last element of `thir.exprs`.
-assert_eq!(expr.as_usize(), thir.exprs.len() - 1);
-
 // Figure out what primary body this item has.
 let body = tcx.hir_body_owned_by(fn_def);
 let span_with_body = tcx.hir_span_with_body(fn_id);

compiler/rustc_mir_build/src/thir/print.rs

@@ -8,10 +8,10 @@ use rustc_span::def_id::LocalDefId;
 /// Create a THIR tree for debugging.
 pubfnthir_tree(tcx:TyCtxt<'_>,owner_def:LocalDefId) -> String{
 matchsuper::cx::thir_body(tcx, owner_def){
-Ok((thir,_)) => {
+Ok((thir,expr)) => {
 let thir = thir.steal();
 letmut printer = ThirPrinter::new(&thir);
- printer.print();
+ printer.print(expr);
  printer.into_buffer()
 }
 Err(_) => "error".into(),
@@ -58,16 +58,15 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
 }
 }
 
-fnprint(&mutself){
+fnprint(&mutself,body_expr:ExprId){
 print_indented!(self,"params: [",0);
 for param inself.thir.params.iter(){
 self.print_param(param,1);
 }
 print_indented!(self,"]",0);
 
 print_indented!(self,"body:",0);
-let expr = ExprId::from_usize(self.thir.exprs.len() - 1);
-self.print_expr(expr,1);
+self.print_expr(body_expr,1);
 }
 
 fninto_buffer(self) -> String{