run unsafety checking before dead block collection

Fixes #45087.

src/librustc/dep_graph/dep_node.rs

@@ -473,6 +473,7 @@ define_dep_nodes!( <'tcx>
     // Represents the MIR for a fn; also used as the task node for
     // things read/modify that MIR.
     [] MirConstQualif(DefId),
+    [] MirBuilt(DefId),
     [] MirConst(DefId),
     [] MirValidated(DefId),
     [] MirOptimized(DefId),
@@ -812,4 +813,3 @@ impl WorkProductId {
 impl_stable_hash_for!(struct ::dep_graph::WorkProductId {
     hash
 });
-

src/librustc/ty/maps/mod.rs

@@ -151,6 +151,10 @@ define_maps! { <'tcx>
     /// the value isn't known except to the pass itself.
     [] fn mir_const_qualif: MirConstQualif(DefId) -> (u8, Rc<IdxSetBuf<mir::Local>>),
 
+    /// Fetch the MIR for a given def-id right after it's built - this includes
+    /// unreachable code.
+    [] fn mir_built: MirBuilt(DefId) -> &'tcx Steal<mir::Mir<'tcx>>,
+
     /// Fetch the MIR for a given def-id up till the point where it is
     /// ready for const evaluation.
     ///

src/librustc/ty/maps/plumbing.rs

@@ -712,6 +712,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
             force!(crate_inherent_impls_overlap_check, LOCAL_CRATE)
         },
         DepKind::PrivacyAccessLevels => { force!(privacy_access_levels, LOCAL_CRATE); }
+        DepKind::MirBuilt => { force!(mir_built, def_id!()); }
         DepKind::MirConstQualif => { force!(mir_const_qualif, def_id!()); }
         DepKind::MirConst => { force!(mir_const, def_id!()); }
         DepKind::MirValidated => { force!(mir_validated, def_id!()); }
@@ -852,4 +853,3 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
 
     true
 }
-

src/librustc_mir/transform/check_unsafety.rs

@@ -344,8 +344,8 @@ fn unsafety_violations<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) ->
     debug!("unsafety_violations({:?})", def_id);
 
     // NB: this borrow is valid because all the consumers of
-    // `mir_const` force this.
-    let mir = &tcx.mir_const(def_id).borrow();
+    // `mir_built` force this.
+    let mir = &tcx.mir_built(def_id).borrow();
 
     let visibility_scope_info = match mir.visibility_scope_info {
         ClearOnDecode::Set(ref data) => data,

src/librustc_mir/transform/mod.rs

@@ -50,6 +50,7 @@ pub(crate) fn provide(providers: &mut Providers) {
     self::check_unsafety::provide(providers);
     *providers = Providers {
         mir_keys,
+        mir_built,
         mir_const,
         mir_validated,
         optimized_mir,
@@ -103,9 +104,17 @@ fn mir_keys<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, krate: CrateNum)
     Rc::new(set)
 }
 
+fn mir_built<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx Steal<Mir<'tcx>> {
+    let mir = build::mir_build(tcx, def_id);
+    tcx.alloc_steal_mir(mir)
+}
+
 fn mir_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx Steal<Mir<'tcx>> {
-    let mut mir = build::mir_build(tcx, def_id);
+    // Unsafety check uses the raw mir, so make sure it is run
+    let _ = tcx.unsafety_violations(def_id);
+
     let source = MirSource::from_local_def_id(tcx, def_id);
+    let mut mir = tcx.mir_built(def_id).steal();
     transform::run_suite(tcx, source, MIR_CONST, &mut mir);
     tcx.alloc_steal_mir(mir)
 }
@@ -117,7 +126,6 @@ fn mir_validated<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx
         // this point, before we steal the mir-const result.
         let _ = tcx.mir_const_qualif(def_id);
     }
-    let _ = tcx.unsafety_violations(def_id);
 
     let mut mir = tcx.mir_const(def_id).steal();
     transform::run_suite(tcx, source, MIR_VALIDATED, &mut mir);

src/test/compile-fail/issue-45087-unreachable-unsafe.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    return;
+    *(1 as *mut u32) = 42;
+    //~^ ERROR dereference of raw pointer requires unsafe
+}