Merge pull request #916 from bjorn3/fn_once_for_box_without_alloca

Emulate `<Box<F> as FnOnce>::call_once` without `alloca`

Author: bjorn3

patches/0015-Remove-usage-of-unsized-locals.patch

@@ -1 +1 @@
-nightly-2020-03-07
+nightly-2020-03-10

patches/0017-Fix-libtest-compilation.patch

@@ -288,7 +288,7 @@ fn local_place<'tcx>(
     fx.local_map[&local]
 }
 
-pub fn codegen_fn_prelude(fx: &mut FunctionCx<'_, '_, impl Backend>, start_block: Block) {
+pub fn codegen_fn_prelude(fx: &mut FunctionCx<'_, '_, impl Backend>, start_block: Block, should_codegen_locals: bool) {
     let ssa_analyzed = crate::analyze::analyze(fx);
 
     #[cfg(debug_assertions)]
@@ -405,13 +405,17 @@ pub fn codegen_fn_prelude(fx: &mut FunctionCx<'_, '_, impl Backend>, start_block
         }
     }
 
-    for local in fx.mir.vars_and_temps_iter() {
-        let ty = fx.monomorphize(&fx.mir.local_decls[local].ty);
-        let layout = fx.layout_of(ty);
+    // HACK should_codegen_locals required for the ``implement `<Box<F> as FnOnce>::call_once`
+    // without `alloca``` hack in `base::trans_fn`.
+    if should_codegen_locals {
+        for local in fx.mir.vars_and_temps_iter() {
+            let ty = fx.monomorphize(&fx.mir.local_decls[local].ty);
+            let layout = fx.layout_of(ty);
 
-        let is_ssa = ssa_analyzed[local] == crate::analyze::SsaKind::Ssa;
+            let is_ssa = ssa_analyzed[local] == crate::analyze::SsaKind::Ssa;
 
-        local_place(fx, local, layout, is_ssa);
+            local_place(fx, local, layout, is_ssa);
+        }
     }
 
     fx.bcx