Fix trans_get_discriminant for uninhabited types

Author: bjorn3

src/base.rs

@@ -739,7 +739,7 @@ pub fn trans_get_discriminant<'a, 'tcx: 'a>(
     let layout = place.layout();
 
     if layout.abi == layout::Abi::Uninhabited {
-        trap_unreachable(&mut fx.bcx);
+        return trap_unreachable_ret_value(fx, dest_layout);
     }
     match layout.variants {
         layout::Variants::Single { index } => {

src/trap.rs

@@ -1,6 +1,4 @@
-use cranelift::prelude::*;
-
-use cranelift::codegen::ir::TrapCode;
+use crate::prelude::*;
 
 /// Trap code: user0
 pub fn trap_panic(bcx: &mut FunctionBuilder) {
@@ -11,3 +9,10 @@ pub fn trap_panic(bcx: &mut FunctionBuilder) {
 pub fn trap_unreachable(bcx: &mut FunctionBuilder) {
     bcx.ins().trap(TrapCode::User(!0));
 }
+
+pub fn trap_unreachable_ret_value<'tcx>(fx: &mut FunctionCx<'_, 'tcx, impl cranelift_module::Backend>, dest_layout: TyLayout<'tcx>) -> CValue<'tcx> {
+    let true_ = fx.bcx.ins().iconst(types::I32, 1);
+    fx.bcx.ins().trapnz(true_, TrapCode::User(!0));
+    let zero = fx.bcx.ins().iconst(fx.pointer_type, 0);
+    CValue::ByRef(zero, dest_layout)
+}