Rollup merge of #40372 - nagisa:never-drop, r=eddyb

Do not bother creating StorageLive for TyNever

Keeps MIR cleaner, `StorageLive(_: !)` makes no sense anyway.

r? @eddyb

Author: frewsxcv

src/librustc_mir/build/expr/as_temp.rs

@@ -55,7 +55,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 (https://github.com/rust-lang/rust/issues/39283)");
         }
 
-        if temp_lifetime.is_some() {
+        if !expr_ty.is_never() && temp_lifetime.is_some() {
             this.cfg.push(block, Statement {
                 source_info: source_info,
                 kind: StatementKind::StorageLive(temp.clone())

src/test/mir-opt/issue-38669.rs

@@ -35,7 +35,6 @@ fn main() {
 //     }
 //
 //     bb2: {
-//         StorageLive(_6);
 //         _0 = ();
 //         StorageDead(_4);
 //         StorageDead(_1);