[MIR] Add Storage{Live,Dead} statements to emit llvm.lifetime.{start,end}.

21 files changed, 359 insertions, 59 deletions

diff --git a/src/librustc/mir/repr.rs b/src/librustc/mir/repr.rs
index 08614ca253b..454c1ff8167 100644
--- a/src/librustc/mir/repr.rs
+++ b/src/librustc/mir/repr.rs
@@ -688,8 +688,17 @@ pub struct Statement<'tcx> {
 
 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub enum StatementKind<'tcx> {
+    /// Write the RHS Rvalue to the LHS Lvalue.
     Assign(Lvalue<'tcx>, Rvalue<'tcx>),
-    SetDiscriminant{ lvalue: Lvalue<'tcx>, variant_index: usize },
+
+    /// Write the discriminant for a variant to the enum Lvalue.
+    SetDiscriminant { lvalue: Lvalue<'tcx>, variant_index: usize },
+
+    /// Start a live range for the storage of the local.
+    StorageLive(Lvalue<'tcx>),
+
+    /// End the current live range for the storage of the local.
+    StorageDead(Lvalue<'tcx>),
 }
 
 impl<'tcx> Debug for Statement<'tcx> {
@@ -697,6 +706,8 @@ impl<'tcx> Debug for Statement<'tcx> {
         use self::StatementKind::*;
         match self.kind {
             Assign(ref lv, ref rv) => write!(fmt, "{:?} = {:?}", lv, rv),
+            StorageLive(ref lv) => write!(fmt, "StorageLive({:?})", lv),
+            StorageDead(ref lv) => write!(fmt, "StorageDead({:?})", lv),
             SetDiscriminant{lvalue: ref lv, variant_index: index} => {
                 write!(fmt, "discriminant({:?}) = {:?}", lv, index)
             }
diff --git a/src/librustc/mir/visit.rs b/src/librustc/mir/visit.rs
index d44f00ed2cb..d3526f618a9 100644
--- a/src/librustc/mir/visit.rs
+++ b/src/librustc/mir/visit.rs
@@ -326,6 +326,12 @@ macro_rules! make_mir_visitor {
                     StatementKind::SetDiscriminant{ ref $($mutability)* lvalue, .. } => {
                         self.visit_lvalue(lvalue, LvalueContext::Store);
                     }
+                    StatementKind::StorageLive(ref $($mutability)* lvalue) => {
+                        self.visit_lvalue(lvalue, LvalueContext::StorageLive);
+                    }
+                    StatementKind::StorageDead(ref $($mutability)* lvalue) => {
+                        self.visit_lvalue(lvalue, LvalueContext::StorageDead);
+                    }
                 }
             }
 
@@ -759,4 +765,8 @@ pub enum LvalueContext {
 
     // Consumed as part of an operand
     Consume,
+
+    // Starting and ending a storage live range
+    StorageLive,
+    StorageDead,
 }
diff --git a/src/librustc_borrowck/borrowck/mir/dataflow/impls.rs b/src/librustc_borrowck/borrowck/mir/dataflow/impls.rs
index 57b335bd5ee..90858e4e8b8 100644
--- a/src/librustc_borrowck/borrowck/mir/dataflow/impls.rs
+++ b/src/librustc_borrowck/borrowck/mir/dataflow/impls.rs
@@ -459,6 +459,8 @@ impl<'a, 'tcx> BitDenotation for MovingOutStatements<'a, 'tcx> {
                                          sets.kill_set.add(&moi);
                                      });
             }
+            repr::StatementKind::StorageLive(_) |
+            repr::StatementKind::StorageDead(_) => {}
         }
     }
 
diff --git a/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs b/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs
index ccde429a171..9a4865755e7 100644
--- a/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs
+++ b/src/librustc_borrowck/borrowck/mir/dataflow/sanity_check.rs
@@ -104,6 +104,8 @@ fn each_block<'a, 'tcx, O>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             repr::StatementKind::Assign(ref lvalue, ref rvalue) => {
                 (lvalue, rvalue)
             }
+            repr::StatementKind::StorageLive(_) |
+            repr::StatementKind::StorageDead(_) => continue,
             repr::StatementKind::SetDiscriminant{ .. } =>
                 span_bug!(stmt.source_info.span,
                           "sanity_check should run before Deaggregator inserts SetDiscriminant"),
diff --git a/src/librustc_borrowck/borrowck/mir/gather_moves.rs b/src/librustc_borrowck/borrowck/mir/gather_moves.rs
index e965dcc169c..d2ef3356afb 100644
--- a/src/librustc_borrowck/borrowck/mir/gather_moves.rs
+++ b/src/librustc_borrowck/borrowck/mir/gather_moves.rs
@@ -616,6 +616,8 @@ fn gather_moves<'a, 'tcx>(mir: &Mir<'tcx>, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> MoveD
                         Rvalue::InlineAsm { .. } => {}
                     }
                 }
+                StatementKind::StorageLive(_) |
+                StatementKind::StorageDead(_) => {}
                 StatementKind::SetDiscriminant{ .. } => {
                     span_bug!(stmt.source_info.span,
                               "SetDiscriminant should not exist during borrowck");
diff --git a/src/librustc_borrowck/borrowck/mir/mod.rs b/src/librustc_borrowck/borrowck/mir/mod.rs
index c563fdb8f44..dbee0ea9b00 100644
--- a/src/librustc_borrowck/borrowck/mir/mod.rs
+++ b/src/librustc_borrowck/borrowck/mir/mod.rs
@@ -378,6 +378,8 @@ fn drop_flag_effects_for_location<'a, 'tcx, F>(
                                      move_data.rev_lookup.find(lvalue),
                                      |moi| callback(moi, DropFlagState::Present))
             }
+            repr::StatementKind::StorageLive(_) |
+            repr::StatementKind::StorageDead(_) => {}
         },
         None => {
             debug!("drop_flag_effects: replace {:?}", block.terminator());
diff --git a/src/librustc_mir/build/block.rs b/src/librustc_mir/build/block.rs
index 7e650c5bd3d..34d79732646 100644
--- a/src/librustc_mir/build/block.rs
+++ b/src/librustc_mir/build/block.rs
@@ -68,6 +68,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                                 // FIXME #30046                              ^~~~
                                 this.expr_into_pattern(block, pattern, init)
                             }));
+                        } else {
+                            this.storage_live_for_bindings(block, &pattern);
                         }
 
                         // Enter the visibility scope, after evaluating the initializer.
diff --git a/src/librustc_mir/build/expr/as_temp.rs b/src/librustc_mir/build/expr/as_temp.rs
index da128b8dd56..85128cbbbaf 100644
--- a/src/librustc_mir/build/expr/as_temp.rs
+++ b/src/librustc_mir/build/expr/as_temp.rs
@@ -37,6 +37,14 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         let temp = this.temp(expr_ty.clone());
         let temp_lifetime = expr.temp_lifetime;
         let expr_span = expr.span;
+        let source_info = this.source_info(expr_span);
+
+        if temp_lifetime.is_some() {
+            this.cfg.push(block, Statement {
+                source_info: source_info,
+                kind: StatementKind::StorageLive(temp.clone())
+            });
+        }
 
         // Careful here not to cause an infinite cycle. If we always
         // called `into`, then for lvalues like `x.f`, it would
@@ -49,7 +57,6 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             Category::Lvalue => {
                 let lvalue = unpack!(block = this.as_lvalue(block, expr));
                 let rvalue = Rvalue::Use(Operand::Consume(lvalue));
-                let source_info = this.source_info(expr_span);
                 this.cfg.push_assign(block, source_info, &temp, rvalue);
             }
             _ => {
diff --git a/src/librustc_mir/build/matches/mod.rs b/src/librustc_mir/build/matches/mod.rs
index a94adafa802..ec390704d07 100644
--- a/src/librustc_mir/build/matches/mod.rs
+++ b/src/librustc_mir/build/matches/mod.rs
@@ -122,6 +122,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             PatternKind::Binding { mode: BindingMode::ByValue,
                                    var,
                                    subpattern: None, .. } => {
+                self.storage_live_for_bindings(block, &irrefutable_pat);
                 let lvalue = Lvalue::Var(self.var_indices[&var]);
                 return self.into(&lvalue, block, initializer);
             }
@@ -206,6 +207,43 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         }
         var_scope
     }
+
+    /// Emit `StorageLive` for every binding in the pattern.
+    pub fn storage_live_for_bindings(&mut self,
+                                     block: BasicBlock,
+                                     pattern: &Pattern<'tcx>) {
+        match *pattern.kind {
+            PatternKind::Binding { var, ref subpattern, .. } => {
+                let lvalue = Lvalue::Var(self.var_indices[&var]);
+                let source_info = self.source_info(pattern.span);
+                self.cfg.push(block, Statement {
+                    source_info: source_info,
+                    kind: StatementKind::StorageLive(lvalue)
+                });
+
+                if let Some(subpattern) = subpattern.as_ref() {
+                    self.storage_live_for_bindings(block, subpattern);
+                }
+            }
+            PatternKind::Array { ref prefix, ref slice, ref suffix } |
+            PatternKind::Slice { ref prefix, ref slice, ref suffix } => {
+                for subpattern in prefix.iter().chain(slice).chain(suffix) {
+                    self.storage_live_for_bindings(block, subpattern);
+                }
+            }
+            PatternKind::Constant { .. } | PatternKind::Range { .. } | PatternKind::Wild => {
+            }
+            PatternKind::Deref { ref subpattern } => {
+                self.storage_live_for_bindings(block, subpattern);
+            }
+            PatternKind::Leaf { ref subpatterns } |
+            PatternKind::Variant { ref subpatterns, .. } => {
+                for subpattern in subpatterns {
+                    self.storage_live_for_bindings(block, &subpattern.pattern);
+                }
+            }
+        }
+    }
 }
 
 /// List of blocks for each arm (and potentially other metadata in the
@@ -665,6 +703,10 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             };
 
             let source_info = self.source_info(binding.span);
+            self.cfg.push(block, Statement {
+                source_info: source_info,
+                kind: StatementKind::StorageLive(Lvalue::Var(var_index))
+            });
             self.cfg.push_assign(block, source_info,
                                  &Lvalue::Var(var_index), rvalue);
         }
diff --git a/src/librustc_mir/build/mod.rs b/src/librustc_mir/build/mod.rs
index 362e1e26fdf..814d56f44ac 100644
--- a/src/librustc_mir/build/mod.rs
+++ b/src/librustc_mir/build/mod.rs
@@ -238,7 +238,8 @@ pub fn construct_const<'a, 'gcx, 'tcx>(hir: Cx<'a, 'gcx, 'tcx>,
     let span = tcx.map.span(item_id);
     let mut builder = Builder::new(hir, span);
 
-    let extent = ROOT_CODE_EXTENT;
+    let extent = tcx.region_maps.temporary_scope(ast_expr.id)
+                    .unwrap_or(ROOT_CODE_EXTENT);
     let mut block = START_BLOCK;
     let _ = builder.in_scope(extent, block, |builder| {
         let expr = builder.hir.mirror(ast_expr);
diff --git a/src/librustc_mir/build/scope.rs b/src/librustc_mir/build/scope.rs
index 1703fee9360..cae9e837989 100644
--- a/src/librustc_mir/build/scope.rs
+++ b/src/librustc_mir/build/scope.rs
@@ -107,6 +107,17 @@ pub struct Scope<'tcx> {
     /// `ScopeAuxiliary`, but kept here for convenience
     extent: CodeExtent,
 
+    /// Whether there's anything to do for the cleanup path, that is,
+    /// when unwinding through this scope. This includes destructors,
+    /// but not StorageDead statements, which don't get emitted at all
+    /// for unwinding, for several reasons:
+    ///  * clang doesn't emit llvm.lifetime.end for C++ unwinding
+    ///  * LLVM's memory dependency analysis can't handle it atm
+    ///  * pollutting the cleanup MIR with StorageDead creates
+    ///    landing pads even though there's no actual destructors
+    ///  * freeing up stack space has no effect during unwinding
+    needs_cleanup: bool,
+
     /// set of lvalues to drop when exiting this scope. This starts
     /// out empty but grows as variables are declared during the
     /// building process. This is a stack, so we always drop from the
@@ -139,11 +150,19 @@ struct DropData<'tcx> {
     /// lvalue to drop
     location: Lvalue<'tcx>,
 
-    /// The cached block for the cleanups-on-diverge path. This block
-    /// contains code to run the current drop and all the preceding
-    /// drops (i.e. those having lower index in Drop’s Scope drop
-    /// array)
-    cached_block: Option<BasicBlock>
+    /// Whether this is a full value Drop, or just a StorageDead.
+    kind: DropKind
+}
+
+enum DropKind {
+    Value {
+        /// The cached block for the cleanups-on-diverge path. This block
+        /// contains code to run the current drop and all the preceding
+        /// drops (i.e. those having lower index in Drop’s Scope drop
+        /// array)
+        cached_block: Option<BasicBlock>
+    },
+    Storage
 }
 
 struct FreeData<'tcx> {
@@ -182,7 +201,9 @@ impl<'tcx> Scope<'tcx> {
     fn invalidate_cache(&mut self) {
         self.cached_exits = FnvHashMap();
         for dropdata in &mut self.drops {
-            dropdata.cached_block = None;
+            if let DropKind::Value { ref mut cached_block } = dropdata.kind {
+                *cached_block = None;
+            }
         }
         if let Some(ref mut freedata) = self.free {
             freedata.cached_block = None;
@@ -194,8 +215,14 @@ impl<'tcx> Scope<'tcx> {
     /// Precondition: the caches must be fully filled (i.e. diverge_cleanup is called) in order for
     /// this method to work correctly.
     fn cached_block(&self) -> Option<BasicBlock> {
-        if let Some(data) = self.drops.last() {
-            Some(data.cached_block.expect("drop cache is not filled"))
+        let mut drops = self.drops.iter().rev().filter_map(|data| {
+            match data.kind {
+                DropKind::Value { cached_block } => Some(cached_block),
+                DropKind::Storage => None
+            }
+        });
+        if let Some(cached_block) = drops.next() {
+            Some(cached_block.expect("drop cache is not filled"))
         } else if let Some(ref data) = self.free {
             Some(data.cached_block.expect("free cache is not filled"))
         } else {
@@ -265,6 +292,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             id: id,
             visibility_scope: vis_scope,
             extent: extent,
+            needs_cleanup: false,
             drops: vec![],
             free: None,
             cached_exits: FnvHashMap()
@@ -415,23 +443,37 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                          extent: CodeExtent,
                          lvalue: &Lvalue<'tcx>,
                          lvalue_ty: Ty<'tcx>) {
-        if !self.hir.needs_drop(lvalue_ty) {
-            return
-        }
+        let needs_drop = self.hir.needs_drop(lvalue_ty);
+        let drop_kind = if needs_drop {
+            DropKind::Value { cached_block: None }
+        } else {
+            // Only temps and vars need their storage dead.
+            match *lvalue {
+                Lvalue::Temp(_) | Lvalue::Var(_) => DropKind::Storage,
+                _ => return
+            }
+        };
+
         for scope in self.scopes.iter_mut().rev() {
             if scope.extent == extent {
+                if let DropKind::Value { .. } = drop_kind {
+                    scope.needs_cleanup = true;
+                }
+
                 // No need to invalidate any caches here. The just-scheduled drop will branch into
                 // the drop that comes before it in the vector.
                 scope.drops.push(DropData {
                     span: span,
                     location: lvalue.clone(),
-                    cached_block: None
+                    kind: drop_kind
                 });
                 return;
             } else {
                 // We must invalidate all the cached_blocks leading up to the scope we’re
                 // looking for, because all of the blocks in the chain will become incorrect.
-                scope.invalidate_cache()
+                if let DropKind::Value { .. } = drop_kind {
+                    scope.invalidate_cache()
+                }
             }
         }
         span_bug!(span, "extent {:?} not in scope to drop {:?}", extent, lvalue);
@@ -453,6 +495,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 // We also must invalidate the caches in the scope for which the free is scheduled
                 // because the drops must branch into the free we schedule here.
                 scope.invalidate_cache();
+                scope.needs_cleanup = true;
                 scope.free = Some(FreeData {
                     span: span,
                     value: value.clone(),
@@ -478,10 +521,10 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     /// See module comment for more details. None indicates there’s no
     /// cleanup to do at this point.
     pub fn diverge_cleanup(&mut self) -> Option<BasicBlock> {
-        if self.scopes.iter().all(|scope| scope.drops.is_empty() && scope.free.is_none()) {
+        if !self.scopes.iter().any(|scope| scope.needs_cleanup) {
             return None;
         }
-        assert!(!self.scopes.is_empty()); // or `all` above would be true
+        assert!(!self.scopes.is_empty()); // or `any` above would be false
 
         let unit_temp = self.get_unit_temp();
         let Builder { ref mut hir, ref mut cfg, ref mut scopes,
@@ -510,7 +553,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
             resumeblk
         };
 
-        for scope in scopes.iter_mut().filter(|s| !s.drops.is_empty() || s.free.is_some()) {
+        for scope in scopes.iter_mut().filter(|s| s.needs_cleanup) {
             target = build_diverge_scope(hir.tcx(), cfg, &unit_temp, scope, target);
         }
         Some(target)
@@ -591,21 +634,44 @@ fn build_scope_drops<'tcx>(cfg: &mut CFG<'tcx>,
                            -> BlockAnd<()> {
     let mut iter = scope.drops.iter().rev().peekable();
     while let Some(drop_data) = iter.next() {
-        // Try to find the next block with its cached block for us to diverge into in case the
-        // drop panics.
-        let on_diverge = iter.peek().iter().flat_map(|dd| dd.cached_block.into_iter()).next();
-        // If there’s no `cached_block`s within current scope, we must look for one in the
-        // enclosing scope.
-        let on_diverge = on_diverge.or_else(||{
-            earlier_scopes.iter().rev().flat_map(|s| s.cached_block()).next()
-        });
-        let next = cfg.start_new_block();
-        cfg.terminate(block, scope.source_info(drop_data.span), TerminatorKind::Drop {
-            location: drop_data.location.clone(),
-            target: next,
-            unwind: on_diverge
-        });
-        block = next;
+        let source_info = scope.source_info(drop_data.span);
+        if let DropKind::Value { .. } = drop_data.kind {
+            // Try to find the next block with its cached block
+            // for us to diverge into in case the drop panics.
+            let on_diverge = iter.peek().iter().filter_map(|dd| {
+                match dd.kind {
+                    DropKind::Value { cached_block } => cached_block,
+                    DropKind::Storage => None
+                }
+            }).next();
+            // If there’s no `cached_block`s within current scope,
+            // we must look for one in the enclosing scope.
+            let on_diverge = on_diverge.or_else(||{
+                earlier_scopes.iter().rev().flat_map(|s| s.cached_block()).next()
+            });
+            let next = cfg.start_new_block();
+            cfg.terminate(block, source_info, TerminatorKind::Drop {
+                location: drop_data.location.clone(),
+                target: next,
+                unwind: on_diverge
+            });
+            block = next;
+        }
+        match drop_data.kind {
+            DropKind::Value { .. } |
+            DropKind::Storage => {
+                // Only temps and vars need their storage dead.
+                match drop_data.location {
+                    Lvalue::Temp(_) | Lvalue::Var(_) => {}
+                    _ => continue
+                }
+
+                cfg.push(block, Statement {
+                    source_info: source_info,
+                    kind: StatementKind::StorageDead(drop_data.location.clone())
+                });
+            }
+        }
     }
     block.unit()
 }
@@ -653,7 +719,13 @@ fn build_diverge_scope<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
     // *forward* order, so that we generate drops[0] first (right to
     // left in diagram above).
     for drop_data in &mut scope.drops {
-        target = if let Some(cached_block) = drop_data.cached_block {
+        // Only full value drops are emitted in the diverging path,
+        // not StorageDead.
+        let cached_block = match drop_data.kind {
+            DropKind::Value { ref mut cached_block } => cached_block,
+            DropKind::Storage => continue
+        };
+        target = if let Some(cached_block) = *cached_block {
             cached_block
         } else {
             let block = cfg.start_new_cleanup_block();
@@ -663,7 +735,7 @@ fn build_diverge_scope<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
                               target: target,
                               unwind: None
                           });
-            drop_data.cached_block = Some(block);
+            *cached_block = Some(block);
             block
         };
     }
diff --git a/src/librustc_mir/transform/deaggregator.rs b/src/librustc_mir/transform/deaggregator.rs
index cd6f0ed9cba..cb3010a5cf4 100644
--- a/src/librustc_mir/transform/deaggregator.rs
+++ b/src/librustc_mir/transform/deaggregator.rs
@@ -50,8 +50,7 @@ impl<'tcx> MirPass<'tcx> for Deaggregator {
             let orig_stmt = bb.statements.pop().unwrap();
             let (lhs, rhs) = match orig_stmt.kind {
                 StatementKind::Assign(ref lhs, ref rhs) => (lhs, rhs),
-                StatementKind::SetDiscriminant{ .. } =>
-                    span_bug!(src_info.span, "expected aggregate, not {:?}", orig_stmt.kind),
+                _ => span_bug!(src_info.span, "expected assign, not {:?}", orig_stmt),
             };
             let (agg_kind, operands) = match rhs {
                 &Rvalue::Aggregate(ref agg_kind, ref operands) => (agg_kind, operands),
@@ -114,7 +113,7 @@ fn get_aggregate_statement_index<'a, 'tcx, 'b>(start: usize,
         let ref statement = statements[i];
         let rhs = match statement.kind {
             StatementKind::Assign(_, ref rhs) => rhs,
-            StatementKind::SetDiscriminant{ .. } => continue,
+            _ => continue,
         };
         let (kind, operands) = match rhs {
             &Rvalue::Aggregate(ref kind, ref operands) => (kind, operands),
diff --git a/src/librustc_mir/transform/promote_consts.rs b/src/librustc_mir/transform/promote_consts.rs
index eb0d8697f15..17dd85abd64 100644
--- a/src/librustc_mir/transform/promote_consts.rs
+++ b/src/librustc_mir/transform/promote_consts.rs
@@ -87,8 +87,12 @@ impl<'tcx> Visitor<'tcx> for TempCollector {
         if let Lvalue::Temp(index) = *lvalue {
             // Ignore drops, if the temp gets promoted,
             // then it's constant and thus drop is noop.
-            if let LvalueContext::Drop = context {
-                return;
+            // Storage live ranges are also irrelevant.
+            match context {
+                LvalueContext::Drop |
+                LvalueContext::StorageLive |
+                LvalueContext::StorageDead => return,
+                _ => {}
             }
 
             let temp = &mut self.temps[index];
@@ -219,12 +223,12 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         let (mut rvalue, mut call) = (None, None);
         let source_info = if stmt_idx < no_stmts {
             let statement = &mut self.source[bb].statements[stmt_idx];
-            let mut rhs = match statement.kind {
+            let rhs = match statement.kind {
                 StatementKind::Assign(_, ref mut rhs) => rhs,
-                StatementKind::SetDiscriminant{ .. } =>
-                    span_bug!(statement.source_info.span,
-                              "cannot promote SetDiscriminant {:?}",
-                              statement),
+                _ => {
+                    span_bug!(statement.source_info.span, "{:?} is not an assignment",
+                              statement);
+                }
             };
             if self.keep_original {
                 rvalue = Some(rhs.clone());
@@ -311,11 +315,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                     StatementKind::Assign(_, ref mut rvalue) => {
                         mem::replace(rvalue, Rvalue::Use(new_operand))
                     }
-                    StatementKind::SetDiscriminant{ .. } => {
-                        span_bug!(statement.source_info.span,
-                                  "cannot promote SetDiscriminant {:?}",
-                                  statement);
-                    }
+                    _ => bug!()
                 }
             }
             Candidate::ShuffleIndices(bb) => {
@@ -354,8 +354,10 @@ pub fn promote_candidates<'a, 'tcx>(mir: &mut Mir<'tcx>,
                 let statement = &mir[bb].statements[stmt_idx];
                 let dest = match statement.kind {
                     StatementKind::Assign(ref dest, _) => dest,
-                    StatementKind::SetDiscriminant{ .. } =>
-                        panic!("cannot promote SetDiscriminant"),
+                    _ => {
+                        span_bug!(statement.source_info.span,
+                                  "expected assignment to promote");
+                    }
                 };
                 if let Lvalue::Temp(index) = *dest {
                     if temps[index] == TempState::PromotedOut {
@@ -408,7 +410,9 @@ pub fn promote_candidates<'a, 'tcx>(mir: &mut Mir<'tcx>,
     for block in mir.basic_blocks_mut() {
         block.statements.retain(|statement| {
             match statement.kind {
-                StatementKind::Assign(Lvalue::Temp(index), _) => {
+                StatementKind::Assign(Lvalue::Temp(index), _) |
+                StatementKind::StorageLive(Lvalue::Temp(index)) |
+                StatementKind::StorageDead(Lvalue::Temp(index)) => {
                     !promoted(index)
                 }
                 _ => true
diff --git a/src/librustc_mir/transform/qualify_consts.rs b/src/librustc_mir/transform/qualify_consts.rs
index 7ebc72bcc5f..87a10f1bb5b 100644
--- a/src/librustc_mir/transform/qualify_consts.rs
+++ b/src/librustc_mir/transform/qualify_consts.rs
@@ -854,7 +854,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
 
     fn visit_statement(&mut self, bb: BasicBlock, statement: &Statement<'tcx>) {
         assert_eq!(self.location.block, bb);
-        self.nest(|this| this.super_statement(bb, statement));
+        self.nest(|this| {
+            this.visit_source_info(&statement.source_info);
+            match statement.kind {
+                StatementKind::Assign(ref lvalue, ref rvalue) => {
+                    this.visit_assign(bb, lvalue, rvalue);
+                }
+                StatementKind::SetDiscriminant { .. } |
+                StatementKind::StorageLive(_) |
+                StatementKind::StorageDead(_) => {}
+            }
+        });
         self.location.statement_index += 1;
     }
 
diff --git a/src/librustc_mir/transform/type_check.rs b/src/librustc_mir/transform/type_check.rs
index 934357c9e1d..79e31167f2f 100644
--- a/src/librustc_mir/transform/type_check.rs
+++ b/src/librustc_mir/transform/type_check.rs
@@ -382,6 +382,15 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                                variant_index);
                 };
             }
+            StatementKind::StorageLive(ref lv) |
+            StatementKind::StorageDead(ref lv) => {
+                match *lv {
+                    Lvalue::Temp(_) | Lvalue::Var(_) => {}
+                    _ => {
+                        span_mirbug!(self, stmt, "bad lvalue: expected temp or var");
+                    }
+                }
+            }
         }
     }
 
diff --git a/src/librustc_trans/mir/analyze.rs b/src/librustc_trans/mir/analyze.rs
index d6dbefec034..de5581af291 100644
--- a/src/librustc_trans/mir/analyze.rs
+++ b/src/librustc_trans/mir/analyze.rs
@@ -161,8 +161,11 @@ impl<'mir, 'bcx, 'tcx> Visitor<'tcx> for LocalAnalyzer<'mir, 'bcx, 'tcx> {
                 LvalueContext::Call => {
                     self.mark_assigned(index);
                 }
-                LvalueContext::Consume => {
-                }
+
+                LvalueContext::StorageLive |
+                LvalueContext::StorageDead |
+                LvalueContext::Consume => {}
+
                 LvalueContext::Store |
                 LvalueContext::Inspect |
                 LvalueContext::Borrow { .. } |
@@ -170,6 +173,7 @@ impl<'mir, 'bcx, 'tcx> Visitor<'tcx> for LocalAnalyzer<'mir, 'bcx, 'tcx> {
                 LvalueContext::Projection => {
                     self.mark_as_lvalue(index);
                 }
+
                 LvalueContext::Drop => {
                     let ty = lvalue.ty(self.mir, self.bcx.tcx());
                     let ty = self.bcx.monomorphize(&ty.to_ty(self.bcx.tcx()));
diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs
index 7ca94b6356e..31fee560fe3 100644
--- a/src/librustc_trans/mir/constant.rs
+++ b/src/librustc_trans/mir/constant.rs
@@ -285,6 +285,8 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
                             Err(err) => if failure.is_ok() { failure = Err(err); }
                         }
                     }
+                    mir::StatementKind::StorageLive(_) |
+                    mir::StatementKind::StorageDead(_) => {}
                     mir::StatementKind::SetDiscriminant{ .. } => {
                         span_bug!(span, "SetDiscriminant should not appear in constants?");
                     }
diff --git a/src/librustc_trans/mir/statement.rs b/src/librustc_trans/mir/statement.rs
index 7e3074f4ced..11672089553 100644
--- a/src/librustc_trans/mir/statement.rs
+++ b/src/librustc_trans/mir/statement.rs
@@ -10,6 +10,7 @@
 
 use rustc::mir::repr as mir;
 
+use base;
 use common::{self, BlockAndBuilder};
 
 use super::MirContext;
@@ -71,6 +72,25 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
                 );
                 bcx
             }
+            mir::StatementKind::StorageLive(ref lvalue) => {
+                self.trans_storage_liveness(bcx, lvalue, base::Lifetime::Start)
+            }
+            mir::StatementKind::StorageDead(ref lvalue) => {
+                self.trans_storage_liveness(bcx, lvalue, base::Lifetime::End)
+            }
+        }
+    }
+
+    fn trans_storage_liveness(&self,
+                              bcx: BlockAndBuilder<'bcx, 'tcx>,
+                              lvalue: &mir::Lvalue<'tcx>,
+                              intrinsic: base::Lifetime)
+                              -> BlockAndBuilder<'bcx, 'tcx> {
+        if let Some(index) = self.mir.local_index(lvalue) {
+            if let LocalRef::Lvalue(tr_lval) = self.locals[index] {
+                intrinsic.call(&bcx, tr_lval.llval);
+            }
         }
+        bcx
     }
 }
diff --git a/src/test/codegen/lifetime_start_end.rs b/src/test/codegen/lifetime_start_end.rs
new file mode 100644
index 00000000000..cf91e7a8bcb
--- /dev/null
+++ b/src/test/codegen/lifetime_start_end.rs
@@ -0,0 +1,54 @@
+// Copyright 2016 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.
+
+// compile-flags: -O -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+#![feature(rustc_attrs)]
+
+// CHECK-LABEL: @test
+#[no_mangle]
+#[rustc_mir] // FIXME #27840 MIR has different codegen.
+pub fn test() {
+    let a = 0;
+    &a; // keep variable in an alloca
+
+// CHECK: [[S_a:%[0-9]+]] = bitcast i32* %a to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_a]])
+
+    {
+        let b = &Some(a);
+        &b; // keep variable in an alloca
+
+// CHECK: [[S_b:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"** %b to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_b]])
+
+// CHECK: [[S_tmp2:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"* %tmp2 to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_tmp2]])
+
+// CHECK: [[E_tmp2:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"* %tmp2 to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_tmp2]])
+
+// CHECK: [[E_b:%[0-9]+]] = bitcast %"2.std::option::Option<i32>"** %b to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_b]])
+    }
+
+    let c = 1;
+    &c; // keep variable in an alloca
+
+// CHECK: [[S_c:%[0-9]+]] = bitcast i32* %c to i8*
+// CHECK: call void @llvm.lifetime.start(i{{[0-9 ]+}}, i8* [[S_c]])
+
+// CHECK: [[E_c:%[0-9]+]] = bitcast i32* %c to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_c]])
+
+// CHECK: [[E_a:%[0-9]+]] = bitcast i32* %a to i8*
+// CHECK: call void @llvm.lifetime.end(i{{[0-9 ]+}}, i8* [[E_a]])
+}
diff --git a/src/test/debuginfo/function-arg-initialization.rs b/src/test/debuginfo/function-arg-initialization.rs
index add09384094..57654acaf73 100644
--- a/src/test/debuginfo/function-arg-initialization.rs
+++ b/src/test/debuginfo/function-arg-initialization.rs
@@ -288,8 +288,8 @@ fn while_expr(mut x: u64, y: u64, z: u64) -> u64 {
 }
 
 fn loop_expr(mut x: u64, y: u64, z: u64) -> u64 {
-    loop { // #break
-        x += z;
+    loop {
+        x += z; // #break
 
         if x + y > 1000 {
             return x;
diff --git a/src/test/mir-opt/storage_ranges.rs b/src/test/mir-opt/storage_ranges.rs
new file mode 100644
index 00000000000..b116d9c3c41
--- /dev/null
+++ b/src/test/mir-opt/storage_ranges.rs
@@ -0,0 +1,45 @@
+// Copyright 2016 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() {
+    let a = 0;
+    {
+        let b = &Some(a);
+    }
+    let c = 1;
+}
+
+// END RUST SOURCE
+// START rustc.node4.PreTrans.after.mir
+//     bb0: {
+//         StorageLive(var0);               // scope 0 at storage_ranges.rs:12:9: 12:10
+//         var0 = const 0i32;               // scope 0 at storage_ranges.rs:12:13: 12:14
+//         StorageLive(var1);               // scope 1 at storage_ranges.rs:14:13: 14:14
+//         StorageLive(tmp1);               // scope 1 at storage_ranges.rs:14:18: 14:25
+//         StorageLive(tmp2);               // scope 1 at storage_ranges.rs:14:23: 14:24
+//         tmp2 = var0;                     // scope 1 at storage_ranges.rs:14:23: 14:24
+//         tmp1 = std::prelude::v1::Some<i32>(tmp2,); // scope 1 at storage_ranges.rs:14:18: 14:25
+//         var1 = &tmp1;                    // scope 1 at storage_ranges.rs:14:17: 14:25
+//         StorageDead(tmp2);               // scope 1 at storage_ranges.rs:14:23: 14:24
+//         tmp0 = ();                       // scope 2 at storage_ranges.rs:13:5: 15:6
+//         StorageDead(tmp1);               // scope 1 at storage_ranges.rs:14:18: 14:25
+//         StorageDead(var1);               // scope 1 at storage_ranges.rs:14:13: 14:14
+//         StorageLive(var2);               // scope 1 at storage_ranges.rs:16:9: 16:10
+//         var2 = const 1i32;               // scope 1 at storage_ranges.rs:16:13: 16:14
+//         return = ();                     // scope 3 at storage_ranges.rs:11:11: 17:2
+//         StorageDead(var2);               // scope 1 at storage_ranges.rs:16:9: 16:10
+//         StorageDead(var0);               // scope 0 at storage_ranges.rs:12:9: 12:10
+//         goto -> bb1;                     // scope 0 at storage_ranges.rs:11:1: 17:2
+//     }
+//
+//     bb1: {
+//         return;                          // scope 0 at storage_ranges.rs:11:1: 17:2
+//     }
+// END rustc.node4.PreTrans.after.mir