1 //===- SafeStackColoring.cpp - SafeStack frame coloring -------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "SafeStackColoring.h"
11 #include "llvm/ADT/BitVector.h"
12 #include "llvm/ADT/DenseMap.h"
13 #include "llvm/ADT/DepthFirstIterator.h"
14 #include "llvm/ADT/SmallVector.h"
15 #include "llvm/IR/BasicBlock.h"
16 #include "llvm/IR/CFG.h"
17 #include "llvm/IR/Instruction.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/IntrinsicInst.h"
20 #include "llvm/IR/Intrinsics.h"
21 #include "llvm/IR/User.h"
22 #include "llvm/Support/Casting.h"
23 #include "llvm/Support/CommandLine.h"
24 #include "llvm/Support/Compiler.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include <cassert>
28 #include <tuple>
29 #include <utility>
30 
31 using namespace llvm;
32 using namespace llvm::safestack;
33 
34 #define DEBUG_TYPE "safestackcoloring"
35 
36 // Disabled by default due to PR32143.
37 static cl::opt<bool> ClColoring("safe-stack-coloring",
38                                 cl::desc("enable safe stack coloring"),
39                                 cl::Hidden, cl::init(false));
40 
41 const StackColoring::LiveRange &StackColoring::getLiveRange(AllocaInst *AI) {
42   const auto IT = AllocaNumbering.find(AI);
43   assert(IT != AllocaNumbering.end());
44   return LiveRanges[IT->second];
45 }
46 
47 bool StackColoring::readMarker(Instruction *I, bool *IsStart) {
48   auto *II = dyn_cast<IntrinsicInst>(I);
49   if (!II || (II->getIntrinsicID() != Intrinsic::lifetime_start &&
50               II->getIntrinsicID() != Intrinsic::lifetime_end))
51     return false;
52 
53   *IsStart = II->getIntrinsicID() == Intrinsic::lifetime_start;
54   return true;
55 }
56 
57 void StackColoring::removeAllMarkers() {
58   for (auto *I : Markers) {
59     auto *Op = dyn_cast<Instruction>(I->getOperand(1));
60     I->eraseFromParent();
61     // Remove the operand bitcast, too, if it has no more uses left.
62     if (Op && Op->use_empty())
63       Op->eraseFromParent();
64   }
65 }
66 
67 void StackColoring::collectMarkers() {
68   InterestingAllocas.resize(NumAllocas);
69   DenseMap<BasicBlock *, SmallDenseMap<Instruction *, Marker>> BBMarkerSet;
70 
71   // Compute the set of start/end markers per basic block.
72   for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo) {
73     AllocaInst *AI = Allocas[AllocaNo];
74     SmallVector<Instruction *, 8> WorkList;
75     WorkList.push_back(AI);
76     while (!WorkList.empty()) {
77       Instruction *I = WorkList.pop_back_val();
78       for (User *U : I->users()) {
79         if (auto *BI = dyn_cast<BitCastInst>(U)) {
80           WorkList.push_back(BI);
81           continue;
82         }
83         auto *UI = dyn_cast<Instruction>(U);
84         if (!UI)
85           continue;
86         bool IsStart;
87         if (!readMarker(UI, &IsStart))
88           continue;
89         if (IsStart)
90           InterestingAllocas.set(AllocaNo);
91         BBMarkerSet[UI->getParent()][UI] = {AllocaNo, IsStart};
92         Markers.push_back(UI);
93       }
94     }
95   }
96 
97   // Compute instruction numbering. Only the following instructions are
98   // considered:
99   // * Basic block entries
100   // * Lifetime markers
101   // For each basic block, compute
102   // * the list of markers in the instruction order
103   // * the sets of allocas whose lifetime starts or ends in this BB
104   DEBUG(dbgs() << "Instructions:\n");
105   unsigned InstNo = 0;
106   for (BasicBlock *BB : depth_first(&F)) {
107     DEBUG(dbgs() << "  " << InstNo << ": BB " << BB->getName() << "\n");
108     unsigned BBStart = InstNo++;
109 
110     BlockLifetimeInfo &BlockInfo = BlockLiveness[BB];
111     BlockInfo.Begin.resize(NumAllocas);
112     BlockInfo.End.resize(NumAllocas);
113     BlockInfo.LiveIn.resize(NumAllocas);
114     BlockInfo.LiveOut.resize(NumAllocas);
115 
116     auto &BlockMarkerSet = BBMarkerSet[BB];
117     if (BlockMarkerSet.empty()) {
118       unsigned BBEnd = InstNo;
119       BlockInstRange[BB] = std::make_pair(BBStart, BBEnd);
120       continue;
121     }
122 
123     auto ProcessMarker = [&](Instruction *I, const Marker &M) {
124       DEBUG(dbgs() << "  " << InstNo << ":  "
125                    << (M.IsStart ? "start " : "end   ") << M.AllocaNo << ", "
126                    << *I << "\n");
127 
128       BBMarkers[BB].push_back({InstNo, M});
129 
130       InstructionNumbering[I] = InstNo++;
131 
132       if (M.IsStart) {
133         if (BlockInfo.End.test(M.AllocaNo))
134           BlockInfo.End.reset(M.AllocaNo);
135         BlockInfo.Begin.set(M.AllocaNo);
136       } else {
137         if (BlockInfo.Begin.test(M.AllocaNo))
138           BlockInfo.Begin.reset(M.AllocaNo);
139         BlockInfo.End.set(M.AllocaNo);
140       }
141     };
142 
143     if (BlockMarkerSet.size() == 1) {
144       ProcessMarker(BlockMarkerSet.begin()->getFirst(),
145                     BlockMarkerSet.begin()->getSecond());
146     } else {
147       // Scan the BB to determine the marker order.
148       for (Instruction &I : *BB) {
149         auto It = BlockMarkerSet.find(&I);
150         if (It == BlockMarkerSet.end())
151           continue;
152         ProcessMarker(&I, It->getSecond());
153       }
154     }
155 
156     unsigned BBEnd = InstNo;
157     BlockInstRange[BB] = std::make_pair(BBStart, BBEnd);
158   }
159   NumInst = InstNo;
160 }
161 
162 void StackColoring::calculateLocalLiveness() {
163   bool changed = true;
164   while (changed) {
165     changed = false;
166 
167     for (BasicBlock *BB : depth_first(&F)) {
168       BlockLifetimeInfo &BlockInfo = BlockLiveness[BB];
169 
170       // Compute LiveIn by unioning together the LiveOut sets of all preds.
171       BitVector LocalLiveIn;
172       for (auto *PredBB : predecessors(BB)) {
173         LivenessMap::const_iterator I = BlockLiveness.find(PredBB);
174         assert(I != BlockLiveness.end() && "Predecessor not found");
175         LocalLiveIn |= I->second.LiveOut;
176       }
177 
178       // Compute LiveOut by subtracting out lifetimes that end in this
179       // block, then adding in lifetimes that begin in this block.  If
180       // we have both BEGIN and END markers in the same basic block
181       // then we know that the BEGIN marker comes after the END,
182       // because we already handle the case where the BEGIN comes
183       // before the END when collecting the markers (and building the
184       // BEGIN/END vectors).
185       BitVector LocalLiveOut = LocalLiveIn;
186       LocalLiveOut.reset(BlockInfo.End);
187       LocalLiveOut |= BlockInfo.Begin;
188 
189       // Update block LiveIn set, noting whether it has changed.
190       if (LocalLiveIn.test(BlockInfo.LiveIn)) {
191         changed = true;
192         BlockInfo.LiveIn |= LocalLiveIn;
193       }
194 
195       // Update block LiveOut set, noting whether it has changed.
196       if (LocalLiveOut.test(BlockInfo.LiveOut)) {
197         changed = true;
198         BlockInfo.LiveOut |= LocalLiveOut;
199       }
200     }
201   } // while changed.
202 }
203 
204 void StackColoring::calculateLiveIntervals() {
205   for (auto IT : BlockLiveness) {
206     BasicBlock *BB = IT.getFirst();
207     BlockLifetimeInfo &BlockInfo = IT.getSecond();
208     unsigned BBStart, BBEnd;
209     std::tie(BBStart, BBEnd) = BlockInstRange[BB];
210 
211     BitVector Started, Ended;
212     Started.resize(NumAllocas);
213     Ended.resize(NumAllocas);
214     SmallVector<unsigned, 8> Start;
215     Start.resize(NumAllocas);
216 
217     // LiveIn ranges start at the first instruction.
218     for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo) {
219       if (BlockInfo.LiveIn.test(AllocaNo)) {
220         Started.set(AllocaNo);
221         Start[AllocaNo] = BBStart;
222       }
223     }
224 
225     for (auto &It : BBMarkers[BB]) {
226       unsigned InstNo = It.first;
227       bool IsStart = It.second.IsStart;
228       unsigned AllocaNo = It.second.AllocaNo;
229 
230       if (IsStart) {
231         assert(!Started.test(AllocaNo) || Start[AllocaNo] == BBStart);
232         if (!Started.test(AllocaNo)) {
233           Started.set(AllocaNo);
234           Ended.reset(AllocaNo);
235           Start[AllocaNo] = InstNo;
236         }
237       } else {
238         assert(!Ended.test(AllocaNo));
239         if (Started.test(AllocaNo)) {
240           LiveRanges[AllocaNo].AddRange(Start[AllocaNo], InstNo);
241           Started.reset(AllocaNo);
242         }
243         Ended.set(AllocaNo);
244       }
245     }
246 
247     for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo)
248       if (Started.test(AllocaNo))
249         LiveRanges[AllocaNo].AddRange(Start[AllocaNo], BBEnd);
250   }
251 }
252 
253 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
254 LLVM_DUMP_METHOD void StackColoring::dumpAllocas() {
255   dbgs() << "Allocas:\n";
256   for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo)
257     dbgs() << "  " << AllocaNo << ": " << *Allocas[AllocaNo] << "\n";
258 }
259 
260 LLVM_DUMP_METHOD void StackColoring::dumpBlockLiveness() {
261   dbgs() << "Block liveness:\n";
262   for (auto IT : BlockLiveness) {
263     BasicBlock *BB = IT.getFirst();
264     BlockLifetimeInfo &BlockInfo = BlockLiveness[BB];
265     auto BlockRange = BlockInstRange[BB];
266     dbgs() << "  BB [" << BlockRange.first << ", " << BlockRange.second
267            << "): begin " << BlockInfo.Begin << ", end " << BlockInfo.End
268            << ", livein " << BlockInfo.LiveIn << ", liveout "
269            << BlockInfo.LiveOut << "\n";
270   }
271 }
272 
273 LLVM_DUMP_METHOD void StackColoring::dumpLiveRanges() {
274   dbgs() << "Alloca liveness:\n";
275   for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo) {
276     LiveRange &Range = LiveRanges[AllocaNo];
277     dbgs() << "  " << AllocaNo << ": " << Range << "\n";
278   }
279 }
280 #endif
281 
282 void StackColoring::run() {
283   DEBUG(dumpAllocas());
284 
285   for (unsigned I = 0; I < NumAllocas; ++I)
286     AllocaNumbering[Allocas[I]] = I;
287   LiveRanges.resize(NumAllocas);
288 
289   collectMarkers();
290 
291   if (!ClColoring) {
292     for (auto &R : LiveRanges) {
293       R.SetMaximum(1);
294       R.AddRange(0, 1);
295     }
296     return;
297   }
298 
299   for (auto &R : LiveRanges)
300     R.SetMaximum(NumInst);
301   for (unsigned I = 0; I < NumAllocas; ++I)
302     if (!InterestingAllocas.test(I))
303       LiveRanges[I] = getFullLiveRange();
304 
305   calculateLocalLiveness();
306   DEBUG(dumpBlockLiveness());
307   calculateLiveIntervals();
308   DEBUG(dumpLiveRanges());
309 }
310