Treat drop_in_place as nounwind with -Z panic-in-drop=abort

The AbortUnwindCalls MIR pass will eliminate any unnecessary cleanups
and will prevent any unwinds from leaking out by forcing an abort.

Author: Amanieu

compiler/rustc_mir_transform/src/abort_unwinding_calls.rs

@@ -5,6 +5,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::layout;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_target::spec::abi::Abi;
+use rustc_target::spec::PanicStrategy;
 
 /// A pass that runs which is targeted at ensuring that codegen guarantees about
 /// unwinding are upheld for compilations of panic=abort programs.
@@ -82,10 +83,11 @@ impl<'tcx> MirPass<'tcx> for AbortUnwindingCalls {
                     };
                     layout::fn_can_unwind(tcx, flags, sig.abi())
                 }
-                TerminatorKind::Drop { .. }
-                | TerminatorKind::DropAndReplace { .. }
-                | TerminatorKind::Assert { .. }
-                | TerminatorKind::FalseUnwind { .. } => {
+                TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => {
+                    tcx.sess.opts.debugging_opts.panic_in_drop == PanicStrategy::Unwind
+                        && layout::fn_can_unwind(tcx, CodegenFnAttrFlags::empty(), Abi::Rust)
+                }
+                TerminatorKind::Assert { .. } | TerminatorKind::FalseUnwind { .. } => {
                     layout::fn_can_unwind(tcx, CodegenFnAttrFlags::empty(), Abi::Rust)
                 }
                 _ => continue,

compiler/rustc_typeck/src/collect.rs

@@ -46,7 +46,7 @@ use rustc_session::lint;
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
-use rustc_target::spec::{abi, SanitizerSet};
+use rustc_target::spec::{abi, PanicStrategy, SanitizerSet};
 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
 use std::iter;
 
@@ -2683,6 +2683,13 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
     }
 
+    // With -Z panic-in-drop=abort, drop_in_place never unwinds.
+    if tcx.sess.opts.debugging_opts.panic_in_drop == PanicStrategy::Abort {
+        if Some(id) == tcx.lang_items().drop_in_place_fn() {
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
+        }
+    }
+
     let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
 
     let mut inline_span = None;