expadn abi check + condese & fix tests

Author: beepster4096

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -456,7 +456,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 mir::ProjectionElem::Deref => {
                     // custom allocators can change box's abi, making it unable to be derefed directly
                     if cg_base.layout.ty.is_box()
-                        && matches!(cg_base.layout.abi, Abi::Aggregate { .. })
+                        && matches!(cg_base.layout.abi, Abi::Aggregate { .. } | Abi::Uninhabited)
                     {
                         let ptr = cg_base.project_field(bx, 0).project_field(bx, 0);
 

src/test/ui/box/issue-78459-ice.rs

@@ -1,4 +1,4 @@
-// check-pass
+// build-pass
 #![feature(allocator_api)]
 
 use std::alloc::Allocator;
@@ -18,5 +18,6 @@ unsafe impl Allocator for BigAllocator {
 }
 
 fn main() {
+    Box::new_in((), &std::alloc::Global);
     Box::new_in((), BigAllocator([0; 2]));
 }