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#define DEBUG_TYPE "instsimplify"
18#include "llvm/Function.h"
19#include "llvm/Pass.h"
20#include "llvm/Type.h"
21#include "llvm/ADT/DepthFirstIterator.h"
22#include "llvm/ADT/SmallPtrSet.h"
23#include "llvm/ADT/Statistic.h"
24#include "llvm/Analysis/Dominators.h"
25#include "llvm/Analysis/InstructionSimplify.h"
26#include "llvm/Target/TargetData.h"
27#include "llvm/Transforms/Scalar.h"
28#include "llvm/Transforms/Utils/Local.h"
29using namespace llvm;
30
31STATISTIC(NumSimplified, "Number of redundant instructions removed");
32
33namespace {
34  struct InstSimplifier : public FunctionPass {
35    static char ID; // Pass identification, replacement for typeid
36    InstSimplifier() : FunctionPass(ID) {
37      initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
38    }
39
40    void getAnalysisUsage(AnalysisUsage &AU) const {
41      AU.setPreservesCFG();
42    }
43
44    /// runOnFunction - Remove instructions that simplify.
45    bool runOnFunction(Function &F) {
46      const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
47      const TargetData *TD = getAnalysisIfAvailable<TargetData>();
48      SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
49      bool Changed = false;
50
51      do {
52        for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
53             DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
54          for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) {
55            Instruction *I = BI++;
56            // The first time through the loop ToSimplify is empty and we try to
57            // simplify all instructions.  On later iterations ToSimplify is not
58            // empty and we only bother simplifying instructions that are in it.
59            if (!ToSimplify->empty() && !ToSimplify->count(I))
60              continue;
61            // Don't waste time simplifying unused instructions.
62            if (!I->use_empty())
63              if (Value *V = SimplifyInstruction(I, TD, DT)) {
64                // Mark all uses for resimplification next time round the loop.
65                for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
66                     UI != UE; ++UI)
67                  Next->insert(cast<Instruction>(*UI));
68                I->replaceAllUsesWith(V);
69                ++NumSimplified;
70                Changed = true;
71              }
72            Changed |= RecursivelyDeleteTriviallyDeadInstructions(I);
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  };
84}
85
86char InstSimplifier::ID = 0;
87INITIALIZE_PASS(InstSimplifier, "instsimplify", "Remove redundant instructions",
88                false, false)
89char &llvm::InstructionSimplifierID = InstSimplifier::ID;
90
91// Public interface to the simplify instructions pass.
92FunctionPass *llvm::createInstructionSimplifierPass() {
93  return new InstSimplifier();
94}
95