1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 Managing the scope stack. The scopes are tied to lexical scopes, so as
13 we descend the HAIR, we push a scope on the stack, translate ite
14 contents, and then pop it off. Every scope is named by a
19 When pushing a new scope, we record the current point in the graph (a
20 basic block); this marks the entry to the scope. We then generate more
21 stuff in the control-flow graph. Whenever the scope is exited, either
22 via a `break` or `return` or just by fallthrough, that marks an exit
23 from the scope. Each lexical scope thus corresponds to a single-entry,
24 multiple-exit (SEME) region in the control-flow graph.
26 For now, we keep a mapping from each `CodeExtent` to its
27 corresponding SEME region for later reference (see caveat in next
28 paragraph). This is because region scopes are tied to
29 them. Eventually, when we shift to non-lexical lifetimes, there should
30 be no need to remember this mapping.
32 There is one additional wrinkle, actually, that I wanted to hide from
33 you but duty compels me to mention. In the course of translating
34 matches, it sometimes happen that certain code (namely guards) gets
35 executed multiple times. This means that the scope lexical scope may
36 in fact correspond to multiple, disjoint SEME regions. So in fact our
37 mapping is from one scope to a vector of SEME regions.
41 The primary purpose for scopes is to insert drops: while translating
42 the contents, we also accumulate lvalues that need to be dropped upon
43 exit from each scope. This is done by calling `schedule_drop`. Once a
44 drop is scheduled, whenever we branch out we will insert drops of all
45 those lvalues onto the outgoing edge. Note that we don't know the full
46 set of scheduled drops up front, and so whenever we exit from the
47 scope we only drop the values scheduled thus far. For example, consider
48 the scope S corresponding to this loop:
58 When processing the `let x`, we will add one drop to the scope for
59 `x`. The break will then insert a drop for `x`. When we process `let
60 y`, we will add another drop (in fact, to a subscope, but let's ignore
61 that for now); any later drops would also drop `y`.
65 There are numerous "normal" ways to early exit a scope: `break`,
66 `continue`, `return` (panics are handled separately). Whenever an
67 early exit occurs, the method `exit_scope` is called. It is given the
68 current point in execution where the early exit occurs, as well as the
69 scope you want to branch to (note that all early exits from to some
70 other enclosing scope). `exit_scope` will record this exit point and
73 Panics are handled in a similar fashion, except that a panic always
74 returns out to the `DIVERGE_BLOCK`. To trigger a panic, simply call
75 `panic(p)` with the current point `p`. Or else you can call
76 `diverge_cleanup`, which will produce a block that you can branch to
77 which does the appropriate cleanup and then diverges. `panic(p)`
78 simply calls `diverge_cleanup()` and adds an edge from `p` to the
83 In addition to the normal scope stack, we track a loop scope stack
84 that contains only loops. It tracks where a `break` and `continue`
89 use build::{BlockAnd, BlockAndExtension, Builder, CFG};
90 use rustc::middle::region::{CodeExtent, CodeExtentData};
91 use rustc::middle::lang_items;
92 use rustc::middle::const_val::ConstVal;
93 use rustc::ty::subst::{Kind, Subst};
94 use rustc::ty::{Ty, TyCtxt};
97 use rustc_data_structures::indexed_vec::Idx;
98 use rustc_data_structures::fx::FxHashMap;
100 pub struct Scope<'tcx> {
101 /// The visibility scope this scope was created in.
102 visibility_scope: VisibilityScope,
104 /// the extent of this scope within source code.
107 /// Whether there's anything to do for the cleanup path, that is,
108 /// when unwinding through this scope. This includes destructors,
109 /// but not StorageDead statements, which don't get emitted at all
110 /// for unwinding, for several reasons:
111 /// * clang doesn't emit llvm.lifetime.end for C++ unwinding
112 /// * LLVM's memory dependency analysis can't handle it atm
113 /// * pollutting the cleanup MIR with StorageDead creates
114 /// landing pads even though there's no actual destructors
115 /// * freeing up stack space has no effect during unwinding
118 /// set of lvalues to drop when exiting this scope. This starts
119 /// out empty but grows as variables are declared during the
120 /// building process. This is a stack, so we always drop from the
121 /// end of the vector (top of the stack) first.
122 drops: Vec<DropData<'tcx>>,
124 /// A scope may only have one associated free, because:
126 /// 1. We require a `free` to only be scheduled in the scope of
127 /// `EXPR` in `box EXPR`;
128 /// 2. It only makes sense to have it translated into the diverge-path.
130 /// This kind of drop will be run *after* all the regular drops
131 /// scheduled onto this scope, because drops may have dependencies
132 /// on the allocated memory.
134 /// This is expected to go away once `box EXPR` becomes a sugar
135 /// for placement protocol and gets desugared in some earlier
137 free: Option<FreeData<'tcx>>,
139 /// The cache for drop chain on “normal” exit into a particular BasicBlock.
140 cached_exits: FxHashMap<(BasicBlock, CodeExtent), BasicBlock>,
143 struct DropData<'tcx> {
144 /// span where drop obligation was incurred (typically where lvalue was declared)
148 location: Lvalue<'tcx>,
150 /// Whether this is a full value Drop, or just a StorageDead.
156 /// The cached block for the cleanups-on-diverge path. This block
157 /// contains code to run the current drop and all the preceding
158 /// drops (i.e. those having lower index in Drop’s Scope drop
160 cached_block: Option<BasicBlock>
165 struct FreeData<'tcx> {
166 /// span where free obligation was incurred
169 /// Lvalue containing the allocated box.
172 /// type of item for which the box was allocated for (i.e. the T in Box<T>).
175 /// The cached block containing code to run the free. The block will also execute all the drops
177 cached_block: Option<BasicBlock>
180 #[derive(Clone, Debug)]
181 pub struct BreakableScope<'tcx> {
182 /// Extent of the loop
183 pub extent: CodeExtent,
184 /// Where the body of the loop begins. `None` if block
185 pub continue_block: Option<BasicBlock>,
186 /// Block to branch into when the loop or block terminates (either by being `break`-en out
187 /// from, or by having its condition to become false)
188 pub break_block: BasicBlock,
189 /// The destination of the loop/block expression itself (i.e. where to put the result of a
190 /// `break` expression)
191 pub break_destination: Lvalue<'tcx>,
194 impl<'tcx> Scope<'tcx> {
195 /// Invalidate all the cached blocks in the scope.
197 /// Should always be run for all inner scopes when a drop is pushed into some scope enclosing a
198 /// larger extent of code.
200 /// `unwind` controls whether caches for the unwind branch are also invalidated.
201 fn invalidate_cache(&mut self, unwind: bool) {
202 self.cached_exits.clear();
203 if !unwind { return; }
204 for dropdata in &mut self.drops {
205 if let DropKind::Value { ref mut cached_block } = dropdata.kind {
206 *cached_block = None;
209 if let Some(ref mut freedata) = self.free {
210 freedata.cached_block = None;
214 /// Returns the cached entrypoint for diverging exit from this scope.
216 /// Precondition: the caches must be fully filled (i.e. diverge_cleanup is called) in order for
217 /// this method to work correctly.
218 fn cached_block(&self) -> Option<BasicBlock> {
219 let mut drops = self.drops.iter().rev().filter_map(|data| {
221 DropKind::Value { cached_block } => Some(cached_block),
222 DropKind::Storage => None
225 if let Some(cached_block) = drops.next() {
226 Some(cached_block.expect("drop cache is not filled"))
227 } else if let Some(ref data) = self.free {
228 Some(data.cached_block.expect("free cache is not filled"))
234 /// Given a span and this scope's visibility scope, make a SourceInfo.
235 fn source_info(&self, span: Span) -> SourceInfo {
238 scope: self.visibility_scope
243 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
244 // Adding and removing scopes
245 // ==========================
246 /// Start a breakable scope, which tracks where `continue` and `break`
247 /// should branch to. See module comment for more details.
249 /// Returns the might_break attribute of the BreakableScope used.
250 pub fn in_breakable_scope<F, R>(&mut self,
251 loop_block: Option<BasicBlock>,
252 break_block: BasicBlock,
253 break_destination: Lvalue<'tcx>,
255 where F: FnOnce(&mut Builder<'a, 'gcx, 'tcx>) -> R
257 let extent = self.topmost_scope();
258 let scope = BreakableScope {
260 continue_block: loop_block,
261 break_block: break_block,
262 break_destination: break_destination,
264 self.breakable_scopes.push(scope);
266 let breakable_scope = self.breakable_scopes.pop().unwrap();
267 assert!(breakable_scope.extent == extent);
271 /// Convenience wrapper that pushes a scope and then executes `f`
272 /// to build its contents, popping the scope afterwards.
273 pub fn in_scope<F, R>(&mut self, extent: CodeExtent, mut block: BasicBlock, f: F) -> BlockAnd<R>
274 where F: FnOnce(&mut Builder<'a, 'gcx, 'tcx>) -> BlockAnd<R>
276 debug!("in_scope(extent={:?}, block={:?})", extent, block);
277 self.push_scope(extent);
278 let rv = unpack!(block = f(self));
279 unpack!(block = self.pop_scope(extent, block));
280 debug!("in_scope: exiting extent={:?} block={:?}", extent, block);
284 /// Push a scope onto the stack. You can then build code in this
285 /// scope and call `pop_scope` afterwards. Note that these two
286 /// calls must be paired; using `in_scope` as a convenience
287 /// wrapper maybe preferable.
288 pub fn push_scope(&mut self, extent: CodeExtent) {
289 debug!("push_scope({:?})", extent);
290 let vis_scope = self.visibility_scope;
291 self.scopes.push(Scope {
292 visibility_scope: vis_scope,
294 needs_cleanup: false,
297 cached_exits: FxHashMap()
301 /// Pops a scope, which should have extent `extent`, adding any
302 /// drops onto the end of `block` that are needed. This must
303 /// match 1-to-1 with `push_scope`.
304 pub fn pop_scope(&mut self,
306 mut block: BasicBlock)
308 debug!("pop_scope({:?}, {:?})", extent, block);
309 // We need to have `cached_block`s available for all the drops, so we call diverge_cleanup
310 // to make sure all the `cached_block`s are filled in.
311 self.diverge_cleanup();
312 let scope = self.scopes.pop().unwrap();
313 assert_eq!(scope.extent, extent);
314 unpack!(block = build_scope_drops(&mut self.cfg,
323 /// Branch out of `block` to `target`, exiting all scopes up to
324 /// and including `extent`. This will insert whatever drops are
325 /// needed, as well as tracking this exit for the SEME region. See
326 /// module comment for details.
327 pub fn exit_scope(&mut self,
330 mut block: BasicBlock,
331 target: BasicBlock) {
332 debug!("exit_scope(extent={:?}, block={:?}, target={:?})", extent, block, target);
333 let scope_count = 1 + self.scopes.iter().rev().position(|scope| scope.extent == extent)
335 span_bug!(span, "extent {:?} does not enclose", extent)
337 let len = self.scopes.len();
338 assert!(scope_count < len, "should not use `exit_scope` to pop ALL scopes");
339 let tmp = self.get_unit_temp();
341 let mut rest = &mut self.scopes[(len - scope_count)..];
342 while let Some((scope, rest_)) = {rest}.split_last_mut() {
344 block = if let Some(&e) = scope.cached_exits.get(&(target, extent)) {
345 self.cfg.terminate(block, scope.source_info(span),
346 TerminatorKind::Goto { target: e });
349 let b = self.cfg.start_new_block();
350 self.cfg.terminate(block, scope.source_info(span),
351 TerminatorKind::Goto { target: b });
352 scope.cached_exits.insert((target, extent), b);
355 unpack!(block = build_scope_drops(&mut self.cfg,
360 if let Some(ref free_data) = scope.free {
361 let next = self.cfg.start_new_block();
362 let free = build_free(self.hir.tcx(), &tmp, free_data, next);
363 self.cfg.terminate(block, scope.source_info(span), free);
368 let scope = &self.scopes[len - scope_count];
369 self.cfg.terminate(block, scope.source_info(span),
370 TerminatorKind::Goto { target: target });
373 /// Creates a new visibility scope, nested in the current one.
374 pub fn new_visibility_scope(&mut self, span: Span) -> VisibilityScope {
375 let parent = self.visibility_scope;
376 let scope = VisibilityScope::new(self.visibility_scopes.len());
377 self.visibility_scopes.push(VisibilityScopeData {
379 parent_scope: Some(parent),
386 /// Finds the breakable scope for a given label. This is used for
387 /// resolving `break` and `continue`.
388 pub fn find_breakable_scope(&mut self,
391 -> &mut BreakableScope<'tcx> {
392 // find the loop-scope with the correct id
393 self.breakable_scopes.iter_mut()
395 .filter(|breakable_scope| breakable_scope.extent == label)
397 .unwrap_or_else(|| span_bug!(span, "no enclosing breakable scope found"))
400 /// Given a span and the current visibility scope, make a SourceInfo.
401 pub fn source_info(&self, span: Span) -> SourceInfo {
404 scope: self.visibility_scope
408 /// Returns the extent of the scope which should be exited by a
410 pub fn extent_of_return_scope(&self) -> CodeExtent {
411 // The outermost scope (`scopes[0]`) will be the `CallSiteScope`.
412 // We want `scopes[1]`, which is the `ParameterScope`.
413 assert!(self.scopes.len() >= 2);
414 assert!(match self.hir.tcx().region_maps.code_extent_data(self.scopes[1].extent) {
415 CodeExtentData::ParameterScope { .. } => true,
418 self.scopes[1].extent
421 /// Returns the topmost active scope, which is known to be alive until
422 /// the next scope expression.
423 pub fn topmost_scope(&self) -> CodeExtent {
424 self.scopes.last().expect("topmost_scope: no scopes present").extent
429 /// Indicates that `lvalue` should be dropped on exit from
431 pub fn schedule_drop(&mut self,
434 lvalue: &Lvalue<'tcx>,
435 lvalue_ty: Ty<'tcx>) {
436 let needs_drop = self.hir.needs_drop(lvalue_ty);
437 let drop_kind = if needs_drop {
438 DropKind::Value { cached_block: None }
440 // Only temps and vars need their storage dead.
442 Lvalue::Local(index) if index.index() > self.arg_count => DropKind::Storage,
447 for scope in self.scopes.iter_mut().rev() {
448 let this_scope = scope.extent == extent;
449 // When building drops, we try to cache chains of drops in such a way so these drops
450 // could be reused by the drops which would branch into the cached (already built)
451 // blocks. This, however, means that whenever we add a drop into a scope which already
452 // had some blocks built (and thus, cached) for it, we must invalidate all caches which
453 // might branch into the scope which had a drop just added to it. This is necessary,
454 // because otherwise some other code might use the cache to branch into already built
455 // chain of drops, essentially ignoring the newly added drop.
457 // For example consider there’s two scopes with a drop in each. These are built and
458 // thus the caches are filled:
460 // +--------------------------------------------------------+
461 // | +---------------------------------+ |
462 // | | +--------+ +-------------+ | +---------------+ |
463 // | | | return | <-+ | drop(outer) | <-+ | drop(middle) | |
464 // | | +--------+ +-------------+ | +---------------+ |
465 // | +------------|outer_scope cache|--+ |
466 // +------------------------------|middle_scope cache|------+
468 // Now, a new, inner-most scope is added along with a new drop into both inner-most and
469 // outer-most scopes:
471 // +------------------------------------------------------------+
472 // | +----------------------------------+ |
473 // | | +--------+ +-------------+ | +---------------+ | +-------------+
474 // | | | return | <+ | drop(new) | <-+ | drop(middle) | <--+| drop(inner) |
475 // | | +--------+ | | drop(outer) | | +---------------+ | +-------------+
476 // | | +-+ +-------------+ | |
477 // | +---|invalid outer_scope cache|----+ |
478 // +----=----------------|invalid middle_scope cache|-----------+
480 // If, when adding `drop(new)` we do not invalidate the cached blocks for both
481 // outer_scope and middle_scope, then, when building drops for the inner (right-most)
482 // scope, the old, cached blocks, without `drop(new)` will get used, producing the
485 // The cache and its invalidation for unwind branch is somewhat special. The cache is
486 // per-drop, rather than per scope, which has a several different implications. Adding
487 // a new drop into a scope will not invalidate cached blocks of the prior drops in the
488 // scope. That is true, because none of the already existing drops will have an edge
489 // into a block with the newly added drop.
491 // Note that this code iterates scopes from the inner-most to the outer-most,
492 // invalidating caches of each scope visited. This way bare minimum of the
493 // caches gets invalidated. i.e. if a new drop is added into the middle scope, the
494 // cache of outer scpoe stays intact.
495 let invalidate_unwind = needs_drop && !this_scope;
496 scope.invalidate_cache(invalidate_unwind);
498 if let DropKind::Value { .. } = drop_kind {
499 scope.needs_cleanup = true;
501 let tcx = self.hir.tcx();
502 let extent_span = extent.span(&tcx.region_maps, &tcx.hir).unwrap();
503 // Attribute scope exit drops to scope's closing brace
504 let scope_end = Span { lo: extent_span.hi, .. extent_span};
505 scope.drops.push(DropData {
507 location: lvalue.clone(),
513 span_bug!(span, "extent {:?} not in scope to drop {:?}", extent, lvalue);
516 /// Schedule dropping of a not-yet-fully-initialised box.
518 /// This cleanup will only be translated into unwind branch.
519 /// The extent should be for the `EXPR` inside `box EXPR`.
520 /// There may only be one “free” scheduled in any given scope.
521 pub fn schedule_box_free(&mut self,
524 value: &Lvalue<'tcx>,
526 for scope in self.scopes.iter_mut().rev() {
527 // See the comment in schedule_drop above. The primary difference is that we invalidate
528 // the unwind blocks unconditionally. That’s because the box free may be considered
529 // outer-most cleanup within the scope.
530 scope.invalidate_cache(true);
531 if scope.extent == extent {
532 assert!(scope.free.is_none(), "scope already has a scheduled free!");
533 scope.needs_cleanup = true;
534 scope.free = Some(FreeData {
536 value: value.clone(),
543 span_bug!(span, "extent {:?} not in scope to free {:?}", extent, value);
548 /// Creates a path that performs all required cleanup for unwinding.
550 /// This path terminates in Resume. Returns the start of the path.
551 /// See module comment for more details. None indicates there’s no
552 /// cleanup to do at this point.
553 pub fn diverge_cleanup(&mut self) -> Option<BasicBlock> {
554 if !self.scopes.iter().any(|scope| scope.needs_cleanup) {
557 assert!(!self.scopes.is_empty()); // or `any` above would be false
559 let unit_temp = self.get_unit_temp();
560 let Builder { ref mut hir, ref mut cfg, ref mut scopes,
561 ref mut cached_resume_block, .. } = *self;
563 // Build up the drops in **reverse** order. The end result will
566 // scopes[n] -> scopes[n-1] -> ... -> scopes[0]
568 // However, we build this in **reverse order**. That is, we
569 // process scopes[0], then scopes[1], etc, pointing each one at
570 // the result generates from the one before. Along the way, we
571 // store caches. If everything is cached, we'll just walk right
572 // to left reading the cached results but never created anything.
574 // To start, create the resume terminator.
575 let mut target = if let Some(target) = *cached_resume_block {
578 let resumeblk = cfg.start_new_cleanup_block();
579 cfg.terminate(resumeblk,
580 scopes[0].source_info(self.fn_span),
581 TerminatorKind::Resume);
582 *cached_resume_block = Some(resumeblk);
586 for scope in scopes.iter_mut().filter(|s| s.needs_cleanup) {
587 target = build_diverge_scope(hir.tcx(), cfg, &unit_temp, scope, target);
592 /// Utility function for *non*-scope code to build their own drops
593 pub fn build_drop(&mut self,
596 location: Lvalue<'tcx>,
597 ty: Ty<'tcx>) -> BlockAnd<()> {
598 if !self.hir.needs_drop(ty) {
601 let source_info = self.source_info(span);
602 let next_target = self.cfg.start_new_block();
603 let diverge_target = self.diverge_cleanup();
604 self.cfg.terminate(block, source_info,
605 TerminatorKind::Drop {
608 unwind: diverge_target,
613 /// Utility function for *non*-scope code to build their own drops
614 pub fn build_drop_and_replace(&mut self,
617 location: Lvalue<'tcx>,
618 value: Operand<'tcx>) -> BlockAnd<()> {
619 let source_info = self.source_info(span);
620 let next_target = self.cfg.start_new_block();
621 let diverge_target = self.diverge_cleanup();
622 self.cfg.terminate(block, source_info,
623 TerminatorKind::DropAndReplace {
627 unwind: diverge_target,
632 /// Create an Assert terminator and return the success block.
633 /// If the boolean condition operand is not the expected value,
634 /// a runtime panic will be caused with the given message.
635 pub fn assert(&mut self, block: BasicBlock,
638 msg: AssertMessage<'tcx>,
641 let source_info = self.source_info(span);
643 let success_block = self.cfg.start_new_block();
644 let cleanup = self.diverge_cleanup();
646 self.cfg.terminate(block, source_info,
647 TerminatorKind::Assert {
651 target: success_block,
659 /// Builds drops for pop_scope and exit_scope.
660 fn build_scope_drops<'tcx>(cfg: &mut CFG<'tcx>,
662 earlier_scopes: &[Scope<'tcx>],
663 mut block: BasicBlock,
666 let mut iter = scope.drops.iter().rev().peekable();
667 while let Some(drop_data) = iter.next() {
668 let source_info = scope.source_info(drop_data.span);
669 if let DropKind::Value { .. } = drop_data.kind {
670 // Try to find the next block with its cached block
671 // for us to diverge into in case the drop panics.
672 let on_diverge = iter.peek().iter().filter_map(|dd| {
674 DropKind::Value { cached_block } => cached_block,
675 DropKind::Storage => None
678 // If there’s no `cached_block`s within current scope,
679 // we must look for one in the enclosing scope.
680 let on_diverge = on_diverge.or_else(||{
681 earlier_scopes.iter().rev().flat_map(|s| s.cached_block()).next()
683 let next = cfg.start_new_block();
684 cfg.terminate(block, source_info, TerminatorKind::Drop {
685 location: drop_data.location.clone(),
691 match drop_data.kind {
692 DropKind::Value { .. } |
693 DropKind::Storage => {
694 // Only temps and vars need their storage dead.
695 match drop_data.location {
696 Lvalue::Local(index) if index.index() > arg_count => {}
700 cfg.push(block, Statement {
701 source_info: source_info,
702 kind: StatementKind::StorageDead(drop_data.location.clone())
710 fn build_diverge_scope<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
712 unit_temp: &Lvalue<'tcx>,
713 scope: &mut Scope<'tcx>,
714 mut target: BasicBlock)
717 // Build up the drops in **reverse** order. The end result will
720 // [drops[n]] -...-> [drops[0]] -> [Free] -> [target]
722 // +------------------------------------+
725 // The code in this function reads from right to left. At each
726 // point, we check for cached blocks representing the
727 // remainder. If everything is cached, we'll just walk right to
728 // left reading the cached results but never created anything.
730 let visibility_scope = scope.visibility_scope;
731 let source_info = |span| SourceInfo {
733 scope: visibility_scope
736 // Next, build up any free.
737 if let Some(ref mut free_data) = scope.free {
738 target = if let Some(cached_block) = free_data.cached_block {
741 let into = cfg.start_new_cleanup_block();
742 cfg.terminate(into, source_info(free_data.span),
743 build_free(tcx, unit_temp, free_data, target));
744 free_data.cached_block = Some(into);
749 // Next, build up the drops. Here we iterate the vector in
750 // *forward* order, so that we generate drops[0] first (right to
751 // left in diagram above).
752 for drop_data in &mut scope.drops {
753 // Only full value drops are emitted in the diverging path,
755 let cached_block = match drop_data.kind {
756 DropKind::Value { ref mut cached_block } => cached_block,
757 DropKind::Storage => continue
759 target = if let Some(cached_block) = *cached_block {
762 let block = cfg.start_new_cleanup_block();
763 cfg.terminate(block, source_info(drop_data.span),
764 TerminatorKind::Drop {
765 location: drop_data.location.clone(),
769 *cached_block = Some(block);
777 fn build_free<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
778 unit_temp: &Lvalue<'tcx>,
779 data: &FreeData<'tcx>,
781 -> TerminatorKind<'tcx> {
782 let free_func = tcx.require_lang_item(lang_items::BoxFreeFnLangItem);
783 let substs = tcx.intern_substs(&[Kind::from(data.item_ty)]);
784 TerminatorKind::Call {
785 func: Operand::Constant(Constant {
787 ty: tcx.item_type(free_func).subst(tcx, substs),
788 literal: Literal::Value {
789 value: ConstVal::Function(free_func, substs),
792 args: vec![Operand::Consume(data.value.clone())],
793 destination: Some((unit_temp.clone(), target)),