mir: drop temps outside-in by scheduling the drops inside-out.

Author: eddyb

src/librustc_mir/build/expr/as_temp.rs

@@ -41,7 +41,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
                 span_bug!(expr.span, "no temp_lifetime for expr");
             }
         };
-        this.schedule_drop(expr.span, temp_lifetime, &temp, expr_ty);
+        let expr_span = expr.span;
 
         // Careful here not to cause an infinite cycle. If we always
         // called `into`, then for lvalues like `x.f`, it would
@@ -52,7 +52,6 @@ impl<'a,'tcx> Builder<'a,'tcx> {
         // course) `as_temp`.
         match Category::of(&expr.kind).unwrap() {
             Category::Lvalue => {
-                let expr_span = expr.span;
                 let lvalue = unpack!(block = this.as_lvalue(block, expr));
                 let rvalue = Rvalue::Use(Operand::Consume(lvalue));
                 let scope_id = this.innermost_scope_id();
@@ -63,6 +62,8 @@ impl<'a,'tcx> Builder<'a,'tcx> {
             }
         }
 
+        this.schedule_drop(expr_span, temp_lifetime, &temp, expr_ty);
+
         block.and(temp)
     }
 }

src/test/run-pass/issue-23338-ensure-param-drop-order.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(rustc_attrs)]
-
 // ignore-pretty : (#23623) problems when  ending with // comments
 
 // This test is ensuring that parameters are indeed dropped after
@@ -66,7 +64,6 @@ fn test<'a>(log: d::Log<'a>) {
     d::println(&format!("result {}", result));
 }
 
-#[rustc_no_mir] // FIXME #29855 MIR doesn't handle all drops correctly.
 fn foo<'a>(da0: D<'a>, de1: D<'a>) -> D<'a> {
     d::println("entered foo");
     let de2 = de1.incr();      // creates D(de_2, 2)