Move the implementation to codegen, to use monomorphized types

Author: saethlin

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -153,7 +153,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     let llfn = cx.get_fn(instance);
 
-    let mir = cx.tcx().instance_mir(instance.def);
+    let mut mir = cx.tcx().instance_mir(instance.def);
 
     let fn_abi = cx.fn_abi_of_instance(instance, ty::List::empty());
     debug!("fn_abi: {:?}", fn_abi);
@@ -260,6 +260,31 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     // Apply debuginfo to the newly allocated locals.
     fx.debug_introduce_locals(&mut start_bx);
 
+    if mir.args_iter().any(|arg| {
+        // Find the monomorphized type of our argument
+        let arg_decl = &mir.local_decls[arg];
+        let arg_ty = fx.monomorphize(arg_decl.ty);
+
+        // And check if it is a reference to an uninhabited type
+        let ty = arg_ty.peel_refs();
+        start_bx.layout_of(ty).abi.is_uninhabited()
+    }) {
+        // We're probably not supposed to mutate MIR here.
+        // But since we have an arena, we can just create a clone and replace all references to
+        // the old MIR with the new.
+        let mut body = mir.clone();
+        let blocks = body.basic_blocks.as_mut();
+        blocks.truncate(1);
+        let block = &mut blocks[rustc_middle::mir::START_BLOCK];
+        block.statements.clear();
+        block.terminator.as_mut().unwrap().kind = rustc_middle::mir::TerminatorKind::Unreachable;
+        block.is_cleanup = false;
+
+        // Now we have new MIR, stash it in the TyCtxt arena and swap it in
+        mir = fx.cx.tcx().arena.alloc(body);
+        fx.mir = mir;
+    }
+
     // The builders will be created separately for each basic block at `codegen_block`.
     // So drop the builder of `start_llbb` to avoid having two at the same time.
     drop(start_bx);

compiler/rustc_mir_transform/src/lib.rs

@@ -86,7 +86,6 @@ mod multiple_return_terminators;
 mod normalize_array_len;
 mod nrvo;
 mod prettify;
-mod ralf_refs;
 mod ref_prop;
 mod remove_noop_landing_pads;
 mod remove_storage_markers;
@@ -546,7 +545,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &check_alignment::CheckAlignment,
             &reveal_all::RevealAll, // has to be done before inlining, since inlined code is in RevealAll mode.
             &lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
-            &ralf_refs::RalfRefs,
             &unreachable_prop::UnreachablePropagation,
             &uninhabited_enum_branching::UninhabitedEnumBranching,
             &o1(simplify::SimplifyCfg::AfterUninhabitedEnumBranching),