Use -Z force-dropflag-checks=on/off for emitting sanity-check.

(That is, added config and debugflag a la check-overflow but for drop
flag sanity-check.)

Remove now-unused import of NoDebugInfo from trans::glue.

Author: pnkfelix

src/librustc/session/config.rs

@@ -605,6 +605,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "Print the size of enums and their variants"),
     force_overflow_checks: Option<bool> = (None, parse_opt_bool,
           "Force overflow checks on or off"),
+    force_dropflag_checks: Option<bool> = (None, parse_opt_bool,
+          "Force drop flag checks on or off"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_trans/trans/base.rs

@@ -3029,6 +3029,12 @@ pub fn trans_crate<'tcx>(analysis: ty::CrateAnalysis<'tcx>)
         tcx.sess.opts.debug_assertions
     };
 
+    let check_dropflag = if let Some(v) = tcx.sess.opts.debugging_opts.force_dropflag_checks {
+        v
+    } else {
+        tcx.sess.opts.debug_assertions
+    };
+
     // Before we touch LLVM, make sure that multithreading is enabled.
     unsafe {
         use std::sync::{Once, ONCE_INIT};
@@ -3057,7 +3063,8 @@ pub fn trans_crate<'tcx>(analysis: ty::CrateAnalysis<'tcx>)
                                              Sha256::new(),
                                              link_meta.clone(),
                                              reachable,
-                                             check_overflow);
+                                             check_overflow,
+                                             check_dropflag);
 
     {
         let ccx = shared_ccx.get_ccx(0);

src/librustc_trans/trans/context.rs

@@ -69,6 +69,7 @@ pub struct SharedCrateContext<'tcx> {
     tcx: ty::ctxt<'tcx>,
     stats: Stats,
     check_overflow: bool,
+    check_drop_flag_for_sanity: bool,
 
     available_monomorphizations: RefCell<FnvHashSet<String>>,
     available_drop_glues: RefCell<FnvHashMap<Ty<'tcx>, String>>,
@@ -242,7 +243,8 @@ impl<'tcx> SharedCrateContext<'tcx> {
                symbol_hasher: Sha256,
                link_meta: LinkMeta,
                reachable: NodeSet,
-               check_overflow: bool)
+               check_overflow: bool,
+               check_drop_flag_for_sanity: bool)
                -> SharedCrateContext<'tcx> {
         let (metadata_llcx, metadata_llmod) = unsafe {
             create_context_and_module(&tcx.sess, "metadata")
@@ -271,6 +273,7 @@ impl<'tcx> SharedCrateContext<'tcx> {
                 fn_stats: RefCell::new(Vec::new()),
             },
             check_overflow: check_overflow,
+            check_drop_flag_for_sanity: check_drop_flag_for_sanity,
             available_monomorphizations: RefCell::new(FnvHashSet()),
             available_drop_glues: RefCell::new(FnvHashMap()),
         };
@@ -727,6 +730,13 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
     pub fn check_overflow(&self) -> bool {
         self.shared.check_overflow
     }
+
+    pub fn check_drop_flag_for_sanity(&self) -> bool {
+        // This controls whether we emit a conditional llvm.debugtrap
+        // guarded on whether the dropflag is one of its (two) valid
+        // values.
+        self.shared.check_drop_flag_for_sanity
+    }
 }
 
 fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef> {

src/librustc_trans/trans/glue.rs

@@ -40,7 +40,6 @@ use util::ppaux;
 
 use arena::TypedArena;
 use libc::c_uint;
-use session::config::NoDebugInfo;
 use syntax::ast;
 
 pub fn trans_exchange_free_dyn<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
@@ -237,7 +236,7 @@ fn trans_struct_drop_flag<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
     let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());
     let init_val = C_integral(drop_flag_llty, adt::DTOR_NEEDED as u64, false);
 
-    let bcx = if bcx.tcx().sess.opts.debuginfo == NoDebugInfo {
+    let bcx = if !bcx.ccx().check_drop_flag_for_sanity() {
         bcx
     } else {
         let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());