librustc: Don't use the same alloca for match binding which we reassign to in arm body.

src/librustc/metadata/common.rs

@@ -140,9 +140,10 @@ pub enum astencode_tag { // Reserves 0x40 -- 0x5f
     tag_table_moves_map = 0x52,
     tag_table_capture_map = 0x53,
     tag_table_unboxed_closure_type = 0x54,
+    tag_table_upvar_borrow_map = 0x55,
 }
 static first_astencode_tag: uint = tag_ast as uint;
-static last_astencode_tag: uint = tag_table_unboxed_closure_type as uint;
+static last_astencode_tag: uint = tag_table_upvar_borrow_map as uint;
 impl astencode_tag {
     pub fn from_uint(value : uint) -> Option<astencode_tag> {
         let is_a_tag = first_astencode_tag <= value && value <= last_astencode_tag;

src/librustc/middle/astencode.rs

@@ -18,6 +18,7 @@ use driver::session::Session;
 use metadata::decoder;
 use middle::def;
 use e = metadata::encoder;
+use middle::freevars;
 use middle::freevars::freevar_entry;
 use middle::region;
 use metadata::tydecode;
@@ -551,6 +552,15 @@ impl tr for freevar_entry {
     }
 }
 
+impl tr for ty::UpvarBorrow {
+    fn tr(&self, xcx: &ExtendedDecodeContext) -> ty::UpvarBorrow {
+        ty::UpvarBorrow {
+            kind: self.kind,
+            region: self.region.tr(xcx)
+        }
+    }
+}
+
 // ______________________________________________________________________
 // Encoding and decoding of MethodCallee
 
@@ -1061,7 +1071,29 @@ fn encode_side_tables_for_id(ecx: &e::EncodeContext,
                     Ok(encode_freevar_entry(rbml_w, fv_entry))
                 });
             })
-        })
+        });
+
+        for freevar in fv.iter() {
+            match freevars::get_capture_mode(tcx, id) {
+                freevars::CaptureByRef => {
+                    rbml_w.tag(c::tag_table_upvar_borrow_map, |rbml_w| {
+                        rbml_w.id(id);
+                        rbml_w.tag(c::tag_table_val, |rbml_w| {
+                            let var_id = freevar.def.def_id().node;
+                            let upvar_id = ty::UpvarId {
+                                var_id: var_id,
+                                closure_expr_id: id
+                            };
+                            let upvar_borrow = tcx.upvar_borrow_map.borrow()
+                                                  .get_copy(&upvar_id);
+                            var_id.encode(rbml_w);
+                            upvar_borrow.encode(rbml_w);
+                        })
+                    })
+                }
+                _ => {}
+            }
+        }
     }
 
     let lid = ast::DefId { krate: ast::LOCAL_CRATE, node: id };
@@ -1468,6 +1500,15 @@ fn decode_side_tables(xcx: &ExtendedDecodeContext,
                         }).unwrap().move_iter().collect();
                         dcx.tcx.freevars.borrow_mut().insert(id, fv_info);
                     }
+                    c::tag_table_upvar_borrow_map => {
+                        let var_id: ast::NodeId = Decodable::decode(val_dsr).unwrap();
+                        let upvar_id = ty::UpvarId {
+                            var_id: xcx.tr_id(var_id),
+                            closure_expr_id: id
+                        };
+                        let ub: ty::UpvarBorrow = Decodable::decode(val_dsr).unwrap();
+                        dcx.tcx.upvar_borrow_map.borrow_mut().insert(upvar_id, ub.tr(xcx));
+                    }
                     c::tag_table_tcache => {
                         let pty = val_dsr.read_polytype(xcx);
                         let lid = ast::DefId { krate: ast::LOCAL_CRATE, node: id };

src/librustc/middle/freevars.rs

@@ -14,6 +14,7 @@
 #![allow(non_camel_case_types)]
 
 use middle::def;
+use middle::mem_categorization::Typer;
 use middle::resolve;
 use middle::ty;
 use util::nodemap::{DefIdSet, NodeMap, NodeSet};
@@ -147,11 +148,8 @@ pub fn with_freevars<T>(tcx: &ty::ctxt, fid: ast::NodeId, f: |&[freevar_entry]|
     }
 }
 
-pub fn get_capture_mode(tcx: &ty::ctxt,
-                        closure_expr_id: ast::NodeId)
-                        -> CaptureMode
-{
-    let fn_ty = ty::node_id_to_type(tcx, closure_expr_id);
+pub fn get_capture_mode<T: Typer>(tcx: &T, closure_expr_id: ast::NodeId) -> CaptureMode {
+    let fn_ty = tcx.node_ty(closure_expr_id).ok().expect("couldn't find closure ty?");
     match ty::ty_closure_store(fn_ty) {
         ty::RegionTraitStore(..) => CaptureByRef,
         ty::UniqTraitStore => CaptureByValue

src/librustc/middle/trans/_match.rs

@@ -189,7 +189,9 @@
 #![allow(non_camel_case_types)]
 
 use back::abi;
+use mc = middle::mem_categorization;
 use driver::config::FullDebugInfo;
+use euv = middle::expr_use_visitor;
 use llvm;
 use llvm::{ValueRef, BasicBlockRef};
 use middle::const_eval;
@@ -1292,13 +1294,58 @@ pub fn trans_match<'a>(
     trans_match_inner(bcx, match_expr.id, discr_expr, arms, dest)
 }
 
-fn create_bindings_map(bcx: &Block, pat: Gc<ast::Pat>) -> BindingsMap {
+/// Checks whether the binding in `discr` is assigned to anywhere in the expression `body`
+fn is_discr_reassigned(bcx: &Block, discr: &ast::Expr, body: &ast::Expr) -> bool {
+    match discr.node {
+        ast::ExprPath(..) => match bcx.def(discr.id) {
+            def::DefArg(vid, _) | def::DefBinding(vid, _) |
+            def::DefLocal(vid, _) | def::DefUpvar(vid, _, _, _) => {
+                let mut rc = ReassignmentChecker {
+                    node: vid,
+                    reassigned: false
+                };
+                {
+                    let mut visitor = euv::ExprUseVisitor::new(&mut rc, bcx);
+                    visitor.walk_expr(body);
+                }
+                rc.reassigned
+            }
+            _ => false
+        },
+        _ => false
+    }
+}
+
+struct ReassignmentChecker {
+    node: ast::NodeId,
+    reassigned: bool
+}
+
+impl euv::Delegate for ReassignmentChecker {
+    fn consume(&mut self, _: ast::NodeId, _: Span, _: mc::cmt, _: euv::ConsumeMode) {}
+    fn consume_pat(&mut self, _: &ast::Pat, _: mc::cmt, _: euv::ConsumeMode) {}
+    fn borrow(&mut self, _: ast::NodeId, _: Span, _: mc::cmt, _: ty::Region,
+              _: ty::BorrowKind, _: euv::LoanCause) {}
+    fn decl_without_init(&mut self, _: ast::NodeId, _: Span) {}
+
+    fn mutate(&mut self, _: ast::NodeId, _: Span, cmt: mc::cmt, _: euv::MutateMode) {
+        match cmt.cat {
+            mc::cat_copied_upvar(mc::CopiedUpvar { upvar_id: vid, .. }) |
+            mc::cat_arg(vid) | mc::cat_local(vid) => self.reassigned = self.node == vid,
+            _ => {}
+        }
+    }
+}
+
+fn create_bindings_map(bcx: &Block, pat: Gc<ast::Pat>,
+                      discr: &ast::Expr, body: &ast::Expr) -> BindingsMap {
     // Create the bindings map, which is a mapping from each binding name
     // to an alloca() that will be the value for that local variable.
     // Note that we use the names because each binding will have many ids
     // from the various alternatives.
     let ccx = bcx.ccx();
     let tcx = bcx.tcx();
+    let reassigned = is_discr_reassigned(bcx, discr, body);
     let mut bindings_map = HashMap::new();
     pat_bindings(&tcx.def_map, &*pat, |bm, p_id, span, path1| {
         let ident = path1.node;
@@ -1310,7 +1357,7 @@ fn create_bindings_map(bcx: &Block, pat: Gc<ast::Pat>) -> BindingsMap {
         let trmode;
         match bm {
             ast::BindByValue(_)
-                if !ty::type_moves_by_default(tcx, variable_ty) => {
+                if !ty::type_moves_by_default(tcx, variable_ty) || reassigned => {
                 llmatch = alloca_no_lifetime(bcx,
                                  llvariable_ty.ptr_to(),
                                  "__llmatch");
@@ -1371,7 +1418,7 @@ fn trans_match_inner<'a>(scope_cx: &'a Block<'a>,
     let arm_datas: Vec<ArmData> = arms.iter().map(|arm| ArmData {
         bodycx: fcx.new_id_block("case_body", arm.body.id),
         arm: arm,
-        bindings_map: create_bindings_map(bcx, *arm.pats.get(0))
+        bindings_map: create_bindings_map(bcx, *arm.pats.get(0), discr_expr, &*arm.body)
     }).collect();
 
     let mut static_inliner = StaticInliner { tcx: scope_cx.tcx() };

src/librustc/middle/trans/common.rs

@@ -16,6 +16,7 @@ use driver::session::Session;
 use llvm;
 use llvm::{ValueRef, BasicBlockRef, BuilderRef};
 use llvm::{True, False, Bool};
+use mc = middle::mem_categorization;
 use middle::def;
 use middle::lang_items::LangItem;
 use middle::subst;
@@ -481,6 +482,36 @@ impl<'a> Block<'a> {
     }
 }
 
+impl<'a> mc::Typer for Block<'a> {
+    fn tcx<'a>(&'a self) -> &'a ty::ctxt {
+        self.tcx()
+    }
+
+    fn node_ty(&self, id: ast::NodeId) -> mc::McResult<ty::t> {
+        Ok(node_id_type(self, id))
+    }
+
+    fn node_method_ty(&self, method_call: typeck::MethodCall) -> Option<ty::t> {
+        self.tcx().method_map.borrow().find(&method_call).map(|method| method.ty)
+    }
+
+    fn adjustments<'a>(&'a self) -> &'a RefCell<NodeMap<ty::AutoAdjustment>> {
+        &self.tcx().adjustments
+    }
+
+    fn is_method_call(&self, id: ast::NodeId) -> bool {
+        self.tcx().method_map.borrow().contains_key(&typeck::MethodCall::expr(id))
+    }
+
+    fn temporary_scope(&self, rvalue_id: ast::NodeId) -> Option<ast::NodeId> {
+        self.tcx().region_maps.temporary_scope(rvalue_id)
+    }
+
+    fn upvar_borrow(&self, upvar_id: ty::UpvarId) -> ty::UpvarBorrow {
+        self.tcx().upvar_borrow_map.borrow().get_copy(&upvar_id)
+    }
+}
+
 pub struct Result<'a> {
     pub bcx: &'a Block<'a>,
     pub val: ValueRef

src/librustc/middle/ty.rs

@@ -539,7 +539,7 @@ pub struct UpvarId {
     pub closure_expr_id: ast::NodeId,
 }
 
-#[deriving(Clone, PartialEq, Eq, Hash, Show)]
+#[deriving(Clone, PartialEq, Eq, Hash, Show, Encodable, Decodable)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
     ImmBorrow,
@@ -634,7 +634,7 @@ pub enum BorrowKind {
  *   the closure, so sometimes it is necessary for them to be larger
  *   than the closure lifetime itself.
  */
-#[deriving(PartialEq, Clone)]
+#[deriving(PartialEq, Clone, Encodable, Decodable)]
 pub struct UpvarBorrow {
     pub kind: BorrowKind,
     pub region: ty::Region,

src/test/run-pass/issue-15571.rs

@@ -0,0 +1,64 @@
+// Copyright 2014 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 match_on_local() {
+    let mut foo = Some(box 5i);
+    match foo {
+        None => {},
+        Some(x) => {
+            foo = Some(x);
+        }
+    }
+    println!("'{}'", foo.unwrap());
+}
+
+fn match_on_arg(mut foo: Option<Box<int>>) {
+    match foo {
+        None => {}
+        Some(x) => {
+            foo = Some(x);
+        }
+    }
+    println!("'{}'", foo.unwrap());
+}
+
+fn match_on_binding() {
+    match Some(box 7i) {
+        mut foo => {
+            match foo {
+                None => {},
+                Some(x) => {
+                    foo = Some(x);
+                }
+            }
+            println!("'{}'", foo.unwrap());
+        }
+    }
+}
+
+fn match_on_upvar() {
+    let mut foo = Some(box 8i);
+    (proc() {
+        match foo {
+            None => {},
+            Some(x) => {
+                foo = Some(x);
+            }
+        }
+        println!("'{}'", foo.unwrap());
+    })();
+}
+
+fn main() {
+    match_on_local();
+    match_on_arg(Some(box 6i));
+    match_on_binding();
+    match_on_upvar();
+}

src/test/run-pass/issue-16151.rs

@@ -0,0 +1,38 @@
+// Copyright 2014 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.
+
+use std::mem;
+
+static mut DROP_COUNT: uint = 0;
+
+struct Fragment;
+
+impl Drop for Fragment {
+    fn drop(&mut self) {
+        unsafe {
+            DROP_COUNT += 1;
+        }
+    }
+}
+
+fn main() {
+    {
+        let mut fragments = vec![Fragment, Fragment, Fragment];
+        let _new_fragments: Vec<Fragment> = mem::replace(&mut fragments, vec![])
+            .move_iter()
+            .skip_while(|_fragment| {
+                true
+            }).collect();
+    }
+    unsafe {
+        assert_eq!(DROP_COUNT, 3);
+    }
+}
+