aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm16/lib/Transforms/Scalar/SimplifyCFGPass.cpp
blob: e014f5d1eb042a5361044d9e49d2c5f93cddb021 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
//===- SimplifyCFGPass.cpp - CFG Simplification Pass ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements dead code elimination and basic block merging, along
// with a collection of other peephole control flow optimizations.  For example:
//
//   * Removes basic blocks with no predecessors.
//   * Merges a basic block into its predecessor if there is only one and the
//     predecessor only has one successor.
//   * Eliminates PHI nodes for basic blocks with a single predecessor.
//   * Eliminates a basic block that only contains an unconditional branch.
//   * Changes invoke instructions to nounwind functions to be calls.
//   * Change things like "if (x) if (y)" into "if (x&y)".
//   * etc..
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/SimplifyCFG.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SimplifyCFGOptions.h"
#include <utility>
using namespace llvm;

#define DEBUG_TYPE "simplifycfg"

static cl::opt<unsigned> UserBonusInstThreshold(
    "bonus-inst-threshold", cl::Hidden, cl::init(1),
    cl::desc("Control the number of bonus instructions (default = 1)"));

static cl::opt<bool> UserKeepLoops(
    "keep-loops", cl::Hidden, cl::init(true),
    cl::desc("Preserve canonical loop structure (default = true)"));

static cl::opt<bool> UserSwitchRangeToICmp(
    "switch-range-to-icmp", cl::Hidden, cl::init(false),
    cl::desc(
        "Convert switches into an integer range comparison (default = false)"));

static cl::opt<bool> UserSwitchToLookup(
    "switch-to-lookup", cl::Hidden, cl::init(false),
    cl::desc("Convert switches to lookup tables (default = false)"));

static cl::opt<bool> UserForwardSwitchCond(
    "forward-switch-cond", cl::Hidden, cl::init(false),
    cl::desc("Forward switch condition to phi ops (default = false)"));

static cl::opt<bool> UserHoistCommonInsts(
    "hoist-common-insts", cl::Hidden, cl::init(false),
    cl::desc("hoist common instructions (default = false)"));

static cl::opt<bool> UserSinkCommonInsts(
    "sink-common-insts", cl::Hidden, cl::init(false),
    cl::desc("Sink common instructions (default = false)"));


STATISTIC(NumSimpl, "Number of blocks simplified");

static bool
performBlockTailMerging(Function &F, ArrayRef<BasicBlock *> BBs,
                        std::vector<DominatorTree::UpdateType> *Updates) {
  SmallVector<PHINode *, 1> NewOps;

  // We don't want to change IR just because we can.
  // Only do that if there are at least two blocks we'll tail-merge.
  if (BBs.size() < 2)
    return false;

  if (Updates)
    Updates->reserve(Updates->size() + BBs.size());

  BasicBlock *CanonicalBB;
  Instruction *CanonicalTerm;
  {
    auto *Term = BBs[0]->getTerminator();

    // Create a canonical block for this function terminator type now,
    // placing it *before* the first block that will branch to it.
    CanonicalBB = BasicBlock::Create(
        F.getContext(), Twine("common.") + Term->getOpcodeName(), &F, BBs[0]);
    // We'll also need a PHI node per each operand of the terminator.
    NewOps.resize(Term->getNumOperands());
    for (auto I : zip(Term->operands(), NewOps)) {
      std::get<1>(I) = PHINode::Create(std::get<0>(I)->getType(),
                                       /*NumReservedValues=*/BBs.size(),
                                       CanonicalBB->getName() + ".op");
      std::get<1>(I)->insertInto(CanonicalBB, CanonicalBB->end());
    }
    // Make it so that this canonical block actually has the right
    // terminator.
    CanonicalTerm = Term->clone();
    CanonicalTerm->insertInto(CanonicalBB, CanonicalBB->end());
    // If the canonical terminator has operands, rewrite it to take PHI's.
    for (auto I : zip(NewOps, CanonicalTerm->operands()))
      std::get<1>(I) = std::get<0>(I);
  }

  // Now, go through each block (with the current terminator type)
  // we've recorded, and rewrite it to branch to the new common block.
  const DILocation *CommonDebugLoc = nullptr;
  for (BasicBlock *BB : BBs) {
    auto *Term = BB->getTerminator();
    assert(Term->getOpcode() == CanonicalTerm->getOpcode() &&
           "All blocks to be tail-merged must be the same "
           "(function-terminating) terminator type.");

    // Aha, found a new non-canonical function terminator. If it has operands,
    // forward them to the PHI nodes in the canonical block.
    for (auto I : zip(Term->operands(), NewOps))
      std::get<1>(I)->addIncoming(std::get<0>(I), BB);

    // Compute the debug location common to all the original terminators.
    if (!CommonDebugLoc)
      CommonDebugLoc = Term->getDebugLoc();
    else
      CommonDebugLoc =
          DILocation::getMergedLocation(CommonDebugLoc, Term->getDebugLoc());

    // And turn BB into a block that just unconditionally branches
    // to the canonical block.
    Term->eraseFromParent();
    BranchInst::Create(CanonicalBB, BB);
    if (Updates)
      Updates->push_back({DominatorTree::Insert, BB, CanonicalBB});
  }

  CanonicalTerm->setDebugLoc(CommonDebugLoc);

  return true;
}

static bool tailMergeBlocksWithSimilarFunctionTerminators(Function &F,
                                                          DomTreeUpdater *DTU) {
  SmallMapVector<unsigned /*TerminatorOpcode*/, SmallVector<BasicBlock *, 2>, 4>
      Structure;

  // Scan all the blocks in the function, record the interesting-ones.
  for (BasicBlock &BB : F) {
    if (DTU && DTU->isBBPendingDeletion(&BB))
      continue;

    // We are only interested in function-terminating blocks.
    if (!succ_empty(&BB))
      continue;

    auto *Term = BB.getTerminator();

    // Fow now only support `ret`/`resume` function terminators.
    // FIXME: lift this restriction.
    switch (Term->getOpcode()) {
    case Instruction::Ret:
    case Instruction::Resume:
      break;
    default:
      continue;
    }

    // We can't tail-merge block that contains a musttail call.
    if (BB.getTerminatingMustTailCall())
      continue;

    // Calls to experimental_deoptimize must be followed by a return
    // of the value computed by experimental_deoptimize.
    // I.e., we can not change `ret` to `br` for this block.
    if (auto *CI =
            dyn_cast_or_null<CallInst>(Term->getPrevNonDebugInstruction())) {
      if (Function *F = CI->getCalledFunction())
        if (Intrinsic::ID ID = F->getIntrinsicID())
          if (ID == Intrinsic::experimental_deoptimize)
            continue;
    }

    // PHI nodes cannot have token type, so if the terminator has an operand
    // with token type, we can not tail-merge this kind of function terminators.
    if (any_of(Term->operands(),
               [](Value *Op) { return Op->getType()->isTokenTy(); }))
      continue;

    // Canonical blocks are uniqued based on the terminator type (opcode).
    Structure[Term->getOpcode()].emplace_back(&BB);
  }

  bool Changed = false;

  std::vector<DominatorTree::UpdateType> Updates;

  for (ArrayRef<BasicBlock *> BBs : make_second_range(Structure))
    Changed |= performBlockTailMerging(F, BBs, DTU ? &Updates : nullptr);

  if (DTU)
    DTU->applyUpdates(Updates);

  return Changed;
}

/// Call SimplifyCFG on all the blocks in the function,
/// iterating until no more changes are made.
static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
                                   DomTreeUpdater *DTU,
                                   const SimplifyCFGOptions &Options) {
  bool Changed = false;
  bool LocalChange = true;

  SmallVector<std::pair<const BasicBlock *, const BasicBlock *>, 32> Edges;
  FindFunctionBackedges(F, Edges);
  SmallPtrSet<BasicBlock *, 16> UniqueLoopHeaders;
  for (unsigned i = 0, e = Edges.size(); i != e; ++i)
    UniqueLoopHeaders.insert(const_cast<BasicBlock *>(Edges[i].second));

  SmallVector<WeakVH, 16> LoopHeaders(UniqueLoopHeaders.begin(),
                                      UniqueLoopHeaders.end());

  unsigned IterCnt = 0;
  (void)IterCnt;
  while (LocalChange) {
    assert(IterCnt++ < 1000 && "Iterative simplification didn't converge!");
    LocalChange = false;

    // Loop over all of the basic blocks and remove them if they are unneeded.
    for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
      BasicBlock &BB = *BBIt++;
      if (DTU) {
        assert(
            !DTU->isBBPendingDeletion(&BB) &&
            "Should not end up trying to simplify blocks marked for removal.");
        // Make sure that the advanced iterator does not point at the blocks
        // that are marked for removal, skip over all such blocks.
        while (BBIt != F.end() && DTU->isBBPendingDeletion(&*BBIt))
          ++BBIt;
      }
      if (simplifyCFG(&BB, TTI, DTU, Options, LoopHeaders)) {
        LocalChange = true;
        ++NumSimpl;
      }
    }
    Changed |= LocalChange;
  }
  return Changed;
}

static bool simplifyFunctionCFGImpl(Function &F, const TargetTransformInfo &TTI,
                                    DominatorTree *DT,
                                    const SimplifyCFGOptions &Options) {
  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);

  bool EverChanged = removeUnreachableBlocks(F, DT ? &DTU : nullptr);
  EverChanged |=
      tailMergeBlocksWithSimilarFunctionTerminators(F, DT ? &DTU : nullptr);
  EverChanged |= iterativelySimplifyCFG(F, TTI, DT ? &DTU : nullptr, Options);

  // If neither pass changed anything, we're done.
  if (!EverChanged) return false;

  // iterativelySimplifyCFG can (rarely) make some loops dead.  If this happens,
  // removeUnreachableBlocks is needed to nuke them, which means we should
  // iterate between the two optimizations.  We structure the code like this to
  // avoid rerunning iterativelySimplifyCFG if the second pass of
  // removeUnreachableBlocks doesn't do anything.
  if (!removeUnreachableBlocks(F, DT ? &DTU : nullptr))
    return true;

  do {
    EverChanged = iterativelySimplifyCFG(F, TTI, DT ? &DTU : nullptr, Options);
    EverChanged |= removeUnreachableBlocks(F, DT ? &DTU : nullptr);
  } while (EverChanged);

  return true;
}

static bool simplifyFunctionCFG(Function &F, const TargetTransformInfo &TTI,
                                DominatorTree *DT,
                                const SimplifyCFGOptions &Options) {
  assert((!RequireAndPreserveDomTree ||
          (DT && DT->verify(DominatorTree::VerificationLevel::Full))) &&
         "Original domtree is invalid?");

  bool Changed = simplifyFunctionCFGImpl(F, TTI, DT, Options);

  assert((!RequireAndPreserveDomTree ||
          (DT && DT->verify(DominatorTree::VerificationLevel::Full))) &&
         "Failed to maintain validity of domtree!");

  return Changed;
}

// Command-line settings override compile-time settings.
static void applyCommandLineOverridesToOptions(SimplifyCFGOptions &Options) {
  if (UserBonusInstThreshold.getNumOccurrences())
    Options.BonusInstThreshold = UserBonusInstThreshold;
  if (UserForwardSwitchCond.getNumOccurrences())
    Options.ForwardSwitchCondToPhi = UserForwardSwitchCond;
  if (UserSwitchRangeToICmp.getNumOccurrences())
    Options.ConvertSwitchRangeToICmp = UserSwitchRangeToICmp;
  if (UserSwitchToLookup.getNumOccurrences())
    Options.ConvertSwitchToLookupTable = UserSwitchToLookup;
  if (UserKeepLoops.getNumOccurrences())
    Options.NeedCanonicalLoop = UserKeepLoops;
  if (UserHoistCommonInsts.getNumOccurrences())
    Options.HoistCommonInsts = UserHoistCommonInsts;
  if (UserSinkCommonInsts.getNumOccurrences())
    Options.SinkCommonInsts = UserSinkCommonInsts;
}

SimplifyCFGPass::SimplifyCFGPass() {
  applyCommandLineOverridesToOptions(Options);
}

SimplifyCFGPass::SimplifyCFGPass(const SimplifyCFGOptions &Opts)
    : Options(Opts) {
  applyCommandLineOverridesToOptions(Options);
}

void SimplifyCFGPass::printPipeline(
    raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
  static_cast<PassInfoMixin<SimplifyCFGPass> *>(this)->printPipeline(
      OS, MapClassName2PassName);
  OS << "<";
  OS << "bonus-inst-threshold=" << Options.BonusInstThreshold << ";";
  OS << (Options.ForwardSwitchCondToPhi ? "" : "no-") << "forward-switch-cond;";
  OS << (Options.ConvertSwitchRangeToICmp ? "" : "no-")
     << "switch-range-to-icmp;";
  OS << (Options.ConvertSwitchToLookupTable ? "" : "no-")
     << "switch-to-lookup;";
  OS << (Options.NeedCanonicalLoop ? "" : "no-") << "keep-loops;";
  OS << (Options.HoistCommonInsts ? "" : "no-") << "hoist-common-insts;";
  OS << (Options.SinkCommonInsts ? "" : "no-") << "sink-common-insts";
  OS << ">";
}

PreservedAnalyses SimplifyCFGPass::run(Function &F,
                                       FunctionAnalysisManager &AM) {
  auto &TTI = AM.getResult<TargetIRAnalysis>(F);
  Options.AC = &AM.getResult<AssumptionAnalysis>(F);
  DominatorTree *DT = nullptr;
  if (RequireAndPreserveDomTree)
    DT = &AM.getResult<DominatorTreeAnalysis>(F);
  if (F.hasFnAttribute(Attribute::OptForFuzzing)) {
    Options.setSimplifyCondBranch(false).setFoldTwoEntryPHINode(false);
  } else {
    Options.setSimplifyCondBranch(true).setFoldTwoEntryPHINode(true);
  }
  if (!simplifyFunctionCFG(F, TTI, DT, Options))
    return PreservedAnalyses::all();
  PreservedAnalyses PA;
  if (RequireAndPreserveDomTree)
    PA.preserve<DominatorTreeAnalysis>();
  return PA;
}

namespace {
struct CFGSimplifyPass : public FunctionPass {
  static char ID;
  SimplifyCFGOptions Options;
  std::function<bool(const Function &)> PredicateFtor;

  CFGSimplifyPass(SimplifyCFGOptions Options_ = SimplifyCFGOptions(),
                  std::function<bool(const Function &)> Ftor = nullptr)
      : FunctionPass(ID), Options(Options_), PredicateFtor(std::move(Ftor)) {

    initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());

    // Check for command-line overrides of options for debug/customization.
    applyCommandLineOverridesToOptions(Options);
  }

  bool runOnFunction(Function &F) override {
    if (skipFunction(F) || (PredicateFtor && !PredicateFtor(F)))
      return false;

    Options.AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
    DominatorTree *DT = nullptr;
    if (RequireAndPreserveDomTree)
      DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
    if (F.hasFnAttribute(Attribute::OptForFuzzing)) {
      Options.setSimplifyCondBranch(false)
             .setFoldTwoEntryPHINode(false);
    } else {
      Options.setSimplifyCondBranch(true)
             .setFoldTwoEntryPHINode(true);
    }

    auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
    return simplifyFunctionCFG(F, TTI, DT, Options);
  }
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addRequired<AssumptionCacheTracker>();
    if (RequireAndPreserveDomTree)
      AU.addRequired<DominatorTreeWrapperPass>();
    AU.addRequired<TargetTransformInfoWrapperPass>();
    if (RequireAndPreserveDomTree)
      AU.addPreserved<DominatorTreeWrapperPass>();
    AU.addPreserved<GlobalsAAWrapperPass>();
  }
};
}

char CFGSimplifyPass::ID = 0;
INITIALIZE_PASS_BEGIN(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
                      false)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_END(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
                    false)

// Public interface to the CFGSimplification pass
FunctionPass *
llvm::createCFGSimplificationPass(SimplifyCFGOptions Options,
                                  std::function<bool(const Function &)> Ftor) {
  return new CFGSimplifyPass(Options, std::move(Ftor));
}