1//===------ SimplifyInstructions.cpp - Remove redundant instructions ------===//
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// This is a utility pass used for testing the InstructionSimplify analysis.
11// The analysis is applied to every instruction, and if it simplifies then the
12// instruction is replaced by the simplification.  If you are looking for a pass
13// that performs serious instruction folding, use the instcombine pass instead.
14//
15//===----------------------------------------------------------------------===//
16
17#include "llvm/Transforms/Utils/SimplifyInstructions.h"
18#include "llvm/ADT/DepthFirstIterator.h"
19#include "llvm/ADT/SmallPtrSet.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/Analysis/AssumptionCache.h"
22#include "llvm/Analysis/InstructionSimplify.h"
23#include "llvm/Analysis/TargetLibraryInfo.h"
24#include "llvm/IR/DataLayout.h"
25#include "llvm/IR/Dominators.h"
26#include "llvm/IR/Function.h"
27#include "llvm/IR/Type.h"
28#include "llvm/Pass.h"
29#include "llvm/Transforms/Utils/Local.h"
30#include "llvm/Transforms/Scalar.h"
31using namespace llvm;
32
33#define DEBUG_TYPE "instsimplify"
34
35STATISTIC(NumSimplified, "Number of redundant instructions removed");
36
37static bool runImpl(Function &F, const DominatorTree *DT, const TargetLibraryInfo *TLI,
38                    AssumptionCache *AC) {
39  const DataLayout &DL = F.getParent()->getDataLayout();
40  SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
41  bool Changed = false;
42
43  do {
44    for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
45      // Here be subtlety: the iterator must be incremented before the loop
46      // body (not sure why), so a range-for loop won't work here.
47      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
48        Instruction *I = &*BI++;
49        // The first time through the loop ToSimplify is empty and we try to
50        // simplify all instructions.  On later iterations ToSimplify is not
51        // empty and we only bother simplifying instructions that are in it.
52        if (!ToSimplify->empty() && !ToSimplify->count(I))
53          continue;
54        // Don't waste time simplifying unused instructions.
55        if (!I->use_empty())
56          if (Value *V = SimplifyInstruction(I, DL, TLI, DT, AC)) {
57            // Mark all uses for resimplification next time round the loop.
58            for (User *U : I->users())
59              Next->insert(cast<Instruction>(U));
60            I->replaceAllUsesWith(V);
61            ++NumSimplified;
62            Changed = true;
63          }
64        bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
65        if (res)  {
66          // RecursivelyDeleteTriviallyDeadInstruction can remove
67          // more than one instruction, so simply incrementing the
68          // iterator does not work. When instructions get deleted
69          // re-iterate instead.
70          BI = BB->begin(); BE = BB->end();
71          Changed |= res;
72        }
73      }
74
75    // Place the list of instructions to simplify on the next loop iteration
76    // into ToSimplify.
77    std::swap(ToSimplify, Next);
78    Next->clear();
79  } while (!ToSimplify->empty());
80
81  return Changed;
82}
83
84namespace {
85  struct InstSimplifier : public FunctionPass {
86    static char ID; // Pass identification, replacement for typeid
87    InstSimplifier() : FunctionPass(ID) {
88      initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
89    }
90
91    void getAnalysisUsage(AnalysisUsage &AU) const override {
92      AU.setPreservesCFG();
93      AU.addRequired<AssumptionCacheTracker>();
94      AU.addRequired<TargetLibraryInfoWrapperPass>();
95    }
96
97    /// runOnFunction - Remove instructions that simplify.
98    bool runOnFunction(Function &F) override {
99      if (skipFunction(F))
100        return false;
101
102      const DominatorTreeWrapperPass *DTWP =
103          getAnalysisIfAvailable<DominatorTreeWrapperPass>();
104      const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
105      const TargetLibraryInfo *TLI =
106          &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
107      AssumptionCache *AC =
108          &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
109      return runImpl(F, DT, TLI, AC);
110    }
111  };
112}
113
114char InstSimplifier::ID = 0;
115INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify",
116                      "Remove redundant instructions", false, false)
117INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
118INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
119INITIALIZE_PASS_END(InstSimplifier, "instsimplify",
120                    "Remove redundant instructions", false, false)
121char &llvm::InstructionSimplifierID = InstSimplifier::ID;
122
123// Public interface to the simplify instructions pass.
124FunctionPass *llvm::createInstructionSimplifierPass() {
125  return new InstSimplifier();
126}
127
128PreservedAnalyses InstSimplifierPass::run(Function &F,
129                                      AnalysisManager<Function> &AM) {
130  auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
131  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
132  auto &AC = AM.getResult<AssumptionAnalysis>(F);
133  bool Changed = runImpl(F, DT, &TLI, &AC);
134  if (!Changed)
135    return PreservedAnalyses::all();
136  // FIXME: This should also 'preserve the CFG'.
137  return PreservedAnalyses::none();
138}
139