aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm12/lib/Transforms/Utils/SSAUpdaterBulk.cpp
blob: 917d5e0a1ef0a80e6857d5abe4b54cf104d406c3 (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
//===- SSAUpdaterBulk.cpp - Unstructured SSA Update Tool ------------------===//
//
// 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 the SSAUpdaterBulk class.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/SSAUpdaterBulk.h"
#include "llvm/Analysis/IteratedDominanceFrontier.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"

using namespace llvm;

#define DEBUG_TYPE "ssaupdaterbulk"

/// Helper function for finding a block which should have a value for the given
/// user. For PHI-nodes this block is the corresponding predecessor, for other
/// instructions it's their parent block.
static BasicBlock *getUserBB(Use *U) {
  auto *User = cast<Instruction>(U->getUser());

  if (auto *UserPN = dyn_cast<PHINode>(User))
    return UserPN->getIncomingBlock(*U);
  else
    return User->getParent();
}

/// Add a new variable to the SSA rewriter. This needs to be called before
/// AddAvailableValue or AddUse calls.
unsigned SSAUpdaterBulk::AddVariable(StringRef Name, Type *Ty) {
  unsigned Var = Rewrites.size();
  LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var << ": initialized with Ty = "
                    << *Ty << ", Name = " << Name << "\n");
  RewriteInfo RI(Name, Ty);
  Rewrites.push_back(RI);
  return Var;
}

/// Indicate that a rewritten value is available in the specified block with the
/// specified value.
void SSAUpdaterBulk::AddAvailableValue(unsigned Var, BasicBlock *BB, Value *V) {
  assert(Var < Rewrites.size() && "Variable not found!");
  LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var
                    << ": added new available value" << *V << " in "
                    << BB->getName() << "\n");
  Rewrites[Var].Defines[BB] = V;
}

/// Record a use of the symbolic value. This use will be updated with a
/// rewritten value when RewriteAllUses is called.
void SSAUpdaterBulk::AddUse(unsigned Var, Use *U) {
  assert(Var < Rewrites.size() && "Variable not found!");
  LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var << ": added a use" << *U->get()
                    << " in " << getUserBB(U)->getName() << "\n");
  Rewrites[Var].Uses.push_back(U);
}

/// Return true if the SSAUpdater already has a value for the specified variable
/// in the specified block.
bool SSAUpdaterBulk::HasValueForBlock(unsigned Var, BasicBlock *BB) {
  return (Var < Rewrites.size()) ? Rewrites[Var].Defines.count(BB) : false;
}

// Compute value at the given block BB. We either should already know it, or we
// should be able to recursively reach it going up dominator tree.
Value *SSAUpdaterBulk::computeValueAt(BasicBlock *BB, RewriteInfo &R,
                                      DominatorTree *DT) {
  if (!R.Defines.count(BB)) {
    if (DT->isReachableFromEntry(BB) && PredCache.get(BB).size()) {
      BasicBlock *IDom = DT->getNode(BB)->getIDom()->getBlock();
      Value *V = computeValueAt(IDom, R, DT);
      R.Defines[BB] = V;
    } else
      R.Defines[BB] = UndefValue::get(R.Ty);
  }
  return R.Defines[BB];
}

/// Given sets of UsingBlocks and DefBlocks, compute the set of LiveInBlocks.
/// This is basically a subgraph limited by DefBlocks and UsingBlocks.
static void
ComputeLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &UsingBlocks,
                    const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
                    SmallPtrSetImpl<BasicBlock *> &LiveInBlocks,
                    PredIteratorCache &PredCache) {
  // To determine liveness, we must iterate through the predecessors of blocks
  // where the def is live.  Blocks are added to the worklist if we need to
  // check their predecessors.  Start with all the using blocks.
  SmallVector<BasicBlock *, 64> LiveInBlockWorklist(UsingBlocks.begin(),
                                                    UsingBlocks.end());

  // Now that we have a set of blocks where the phi is live-in, recursively add
  // their predecessors until we find the full region the value is live.
  while (!LiveInBlockWorklist.empty()) {
    BasicBlock *BB = LiveInBlockWorklist.pop_back_val();

    // The block really is live in here, insert it into the set.  If already in
    // the set, then it has already been processed.
    if (!LiveInBlocks.insert(BB).second)
      continue;

    // Since the value is live into BB, it is either defined in a predecessor or
    // live into it to.  Add the preds to the worklist unless they are a
    // defining block.
    for (BasicBlock *P : PredCache.get(BB)) {
      // The value is not live into a predecessor if it defines the value.
      if (DefBlocks.count(P))
        continue;

      // Otherwise it is, add to the worklist.
      LiveInBlockWorklist.push_back(P);
    }
  }
}

/// Perform all the necessary updates, including new PHI-nodes insertion and the
/// requested uses update.
void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
                                    SmallVectorImpl<PHINode *> *InsertedPHIs) {
  for (auto &R : Rewrites) {
    // Compute locations for new phi-nodes.
    // For that we need to initialize DefBlocks from definitions in R.Defines,
    // UsingBlocks from uses in R.Uses, then compute LiveInBlocks, and then use
    // this set for computing iterated dominance frontier (IDF).
    // The IDF blocks are the blocks where we need to insert new phi-nodes.
    ForwardIDFCalculator IDF(*DT);
    LLVM_DEBUG(dbgs() << "SSAUpdater: rewriting " << R.Uses.size()
                      << " use(s)\n");

    SmallPtrSet<BasicBlock *, 2> DefBlocks;
    for (auto &Def : R.Defines)
      DefBlocks.insert(Def.first);
    IDF.setDefiningBlocks(DefBlocks);

    SmallPtrSet<BasicBlock *, 2> UsingBlocks;
    for (Use *U : R.Uses)
      UsingBlocks.insert(getUserBB(U));

    SmallVector<BasicBlock *, 32> IDFBlocks;
    SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
    ComputeLiveInBlocks(UsingBlocks, DefBlocks, LiveInBlocks, PredCache);
    IDF.resetLiveInBlocks();
    IDF.setLiveInBlocks(LiveInBlocks);
    IDF.calculate(IDFBlocks);

    // We've computed IDF, now insert new phi-nodes there.
    SmallVector<PHINode *, 4> InsertedPHIsForVar;
    for (auto *FrontierBB : IDFBlocks) {
      IRBuilder<> B(FrontierBB, FrontierBB->begin());
      PHINode *PN = B.CreatePHI(R.Ty, 0, R.Name);
      R.Defines[FrontierBB] = PN;
      InsertedPHIsForVar.push_back(PN);
      if (InsertedPHIs)
        InsertedPHIs->push_back(PN);
    }

    // Fill in arguments of the inserted PHIs.
    for (auto *PN : InsertedPHIsForVar) {
      BasicBlock *PBB = PN->getParent();
      for (BasicBlock *Pred : PredCache.get(PBB))
        PN->addIncoming(computeValueAt(Pred, R, DT), Pred);
    }

    // Rewrite actual uses with the inserted definitions.
    SmallPtrSet<Use *, 4> ProcessedUses;
    for (Use *U : R.Uses) {
      if (!ProcessedUses.insert(U).second)
        continue;
      Value *V = computeValueAt(getUserBB(U), R, DT);
      Value *OldVal = U->get();
      assert(OldVal && "Invalid use!");
      // Notify that users of the existing value that it is being replaced.
      if (OldVal != V && OldVal->hasValueHandle())
        ValueHandleBase::ValueIsRAUWd(OldVal, V);
      LLVM_DEBUG(dbgs() << "SSAUpdater: replacing " << *OldVal << " with " << *V
                        << "\n");
      U->set(V);
    }
  }
}