1 // Copyright 2012-2014 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.
11 //! An analysis to determine which locals require allocas and
14 use rustc_data_structures::bitvec::BitVector;
15 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
16 use rustc::mir::{self, Location, TerminatorKind};
17 use rustc::mir::visit::{Visitor, LvalueContext};
18 use rustc::mir::traversal;
20 use super::MirContext;
23 pub fn lvalue_locals<'a, 'tcx>(mircx: &MirContext<'a, 'tcx>) -> BitVector {
25 let mut analyzer = LocalAnalyzer::new(mircx);
27 analyzer.visit_mir(mir);
29 for (index, ty) in mir.local_decls.iter().map(|l| l.ty).enumerate() {
30 let ty = mircx.monomorphize(&ty);
31 debug!("local {} has type {:?}", index, ty);
36 common::type_is_zero_size(mircx.ccx, ty)
38 // These sorts of types are immediates that we can store
39 // in an ValueRef without an alloca.
40 assert!(common::type_is_immediate(mircx.ccx, ty) ||
41 common::type_is_fat_ptr(mircx.ccx, ty));
42 } else if common::type_is_imm_pair(mircx.ccx, ty) {
43 // We allow pairs and uses of any of their 2 fields.
45 // These sorts of types require an alloca. Note that
46 // type_is_immediate() may *still* be true, particularly
47 // for newtypes, but we currently force some types
48 // (e.g. structs) into an alloca unconditionally, just so
49 // that we don't have to deal with having two pathways
50 // (gep vs extractvalue etc).
51 analyzer.mark_as_lvalue(mir::Local::new(index));
55 analyzer.lvalue_locals
58 struct LocalAnalyzer<'mir, 'a: 'mir, 'tcx: 'a> {
59 cx: &'mir MirContext<'a, 'tcx>,
60 lvalue_locals: BitVector,
61 seen_assigned: BitVector
64 impl<'mir, 'a, 'tcx> LocalAnalyzer<'mir, 'a, 'tcx> {
65 fn new(mircx: &'mir MirContext<'a, 'tcx>) -> LocalAnalyzer<'mir, 'a, 'tcx> {
68 lvalue_locals: BitVector::new(mircx.mir.local_decls.len()),
69 seen_assigned: BitVector::new(mircx.mir.local_decls.len())
73 fn mark_as_lvalue(&mut self, local: mir::Local) {
74 debug!("marking {:?} as lvalue", local);
75 self.lvalue_locals.insert(local.index());
78 fn mark_assigned(&mut self, local: mir::Local) {
79 if !self.seen_assigned.insert(local.index()) {
80 self.mark_as_lvalue(local);
85 impl<'mir, 'a, 'tcx> Visitor<'tcx> for LocalAnalyzer<'mir, 'a, 'tcx> {
86 fn visit_assign(&mut self,
87 block: mir::BasicBlock,
88 lvalue: &mir::Lvalue<'tcx>,
89 rvalue: &mir::Rvalue<'tcx>,
91 debug!("visit_assign(block={:?}, lvalue={:?}, rvalue={:?})", block, lvalue, rvalue);
93 if let mir::Lvalue::Local(index) = *lvalue {
94 self.mark_assigned(index);
95 if !rvalue::rvalue_creates_operand(rvalue) {
96 self.mark_as_lvalue(index);
99 self.visit_lvalue(lvalue, LvalueContext::Store, location);
102 self.visit_rvalue(rvalue, location);
105 fn visit_terminator_kind(&mut self,
106 block: mir::BasicBlock,
107 kind: &mir::TerminatorKind<'tcx>,
108 location: Location) {
110 mir::TerminatorKind::Call {
111 func: mir::Operand::Constant(mir::Constant {
112 literal: mir::Literal::Item { def_id, .. }, ..
115 } if Some(def_id) == self.cx.ccx.tcx().lang_items.box_free_fn() => {
116 // box_free(x) shares with `drop x` the property that it
117 // is not guaranteed to be statically dominated by the
118 // definition of x, so x must always be in an alloca.
119 if let mir::Operand::Consume(ref lvalue) = args[0] {
120 self.visit_lvalue(lvalue, LvalueContext::Drop, location);
126 self.super_terminator_kind(block, kind, location);
129 fn visit_lvalue(&mut self,
130 lvalue: &mir::Lvalue<'tcx>,
131 context: LvalueContext<'tcx>,
132 location: Location) {
133 debug!("visit_lvalue(lvalue={:?}, context={:?})", lvalue, context);
135 // Allow uses of projections of immediate pair fields.
136 if let mir::Lvalue::Projection(ref proj) = *lvalue {
137 if let mir::Lvalue::Local(_) = proj.base {
138 let ty = proj.base.ty(self.cx.mir, self.cx.ccx.tcx());
140 let ty = self.cx.monomorphize(&ty.to_ty(self.cx.ccx.tcx()));
141 if common::type_is_imm_pair(self.cx.ccx, ty) {
142 if let mir::ProjectionElem::Field(..) = proj.elem {
143 if let LvalueContext::Consume = context {
151 if let mir::Lvalue::Local(index) = *lvalue {
153 LvalueContext::Call => {
154 self.mark_assigned(index);
157 LvalueContext::StorageLive |
158 LvalueContext::StorageDead |
159 LvalueContext::Inspect |
160 LvalueContext::Consume => {}
162 LvalueContext::Store |
163 LvalueContext::Borrow { .. } |
164 LvalueContext::Projection(..) => {
165 self.mark_as_lvalue(index);
168 LvalueContext::Drop => {
169 let ty = lvalue.ty(self.cx.mir, self.cx.ccx.tcx());
170 let ty = self.cx.monomorphize(&ty.to_ty(self.cx.ccx.tcx()));
172 // Only need the lvalue if we're actually dropping it.
173 if self.cx.ccx.shared().type_needs_drop(ty) {
174 self.mark_as_lvalue(index);
180 // A deref projection only reads the pointer, never needs the lvalue.
181 if let mir::Lvalue::Projection(ref proj) = *lvalue {
182 if let mir::ProjectionElem::Deref = proj.elem {
183 return self.visit_lvalue(&proj.base, LvalueContext::Consume, location);
187 self.super_lvalue(lvalue, context, location);
191 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
192 pub enum CleanupKind {
195 Internal { funclet: mir::BasicBlock }
198 pub fn cleanup_kinds<'a, 'tcx>(mir: &mir::Mir<'tcx>) -> IndexVec<mir::BasicBlock, CleanupKind> {
199 fn discover_masters<'tcx>(result: &mut IndexVec<mir::BasicBlock, CleanupKind>,
200 mir: &mir::Mir<'tcx>) {
201 for (bb, data) in mir.basic_blocks().iter_enumerated() {
202 match data.terminator().kind {
203 TerminatorKind::Goto { .. } |
204 TerminatorKind::Resume |
205 TerminatorKind::Return |
206 TerminatorKind::Unreachable |
207 TerminatorKind::SwitchInt { .. } => {
210 TerminatorKind::Call { cleanup: unwind, .. } |
211 TerminatorKind::Assert { cleanup: unwind, .. } |
212 TerminatorKind::DropAndReplace { unwind, .. } |
213 TerminatorKind::Drop { unwind, .. } => {
214 if let Some(unwind) = unwind {
215 debug!("cleanup_kinds: {:?}/{:?} registering {:?} as funclet",
217 result[unwind] = CleanupKind::Funclet;
224 fn propagate<'tcx>(result: &mut IndexVec<mir::BasicBlock, CleanupKind>,
225 mir: &mir::Mir<'tcx>) {
226 let mut funclet_succs = IndexVec::from_elem(None, mir.basic_blocks());
228 let mut set_successor = |funclet: mir::BasicBlock, succ| {
229 match funclet_succs[funclet] {
230 ref mut s @ None => {
231 debug!("set_successor: updating successor of {:?} to {:?}",
235 Some(s) => if s != succ {
236 span_bug!(mir.span, "funclet {:?} has 2 parents - {:?} and {:?}",
242 for (bb, data) in traversal::reverse_postorder(mir) {
243 let funclet = match result[bb] {
244 CleanupKind::NotCleanup => continue,
245 CleanupKind::Funclet => bb,
246 CleanupKind::Internal { funclet } => funclet,
249 debug!("cleanup_kinds: {:?}/{:?}/{:?} propagating funclet {:?}",
250 bb, data, result[bb], funclet);
252 for &succ in data.terminator().successors().iter() {
253 let kind = result[succ];
254 debug!("cleanup_kinds: propagating {:?} to {:?}/{:?}",
255 funclet, succ, kind);
257 CleanupKind::NotCleanup => {
258 result[succ] = CleanupKind::Internal { funclet: funclet };
260 CleanupKind::Funclet => {
261 set_successor(funclet, succ);
263 CleanupKind::Internal { funclet: succ_funclet } => {
264 if funclet != succ_funclet {
265 // `succ` has 2 different funclet going into it, so it must
266 // be a funclet by itself.
268 debug!("promoting {:?} to a funclet and updating {:?}", succ,
270 result[succ] = CleanupKind::Funclet;
271 set_successor(succ_funclet, succ);
272 set_successor(funclet, succ);
280 let mut result = IndexVec::from_elem(CleanupKind::NotCleanup, mir.basic_blocks());
282 discover_masters(&mut result, mir);
283 propagate(&mut result, mir);
284 debug!("cleanup_kinds: result={:?}", result);