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1  //===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===//
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 pass is a simple pass wrapper around the PromoteMemToReg function call
11  // exposed by the Utils library.
12  //
13  //===----------------------------------------------------------------------===//
14  
15  #include "llvm/Transforms/Scalar.h"
16  #include "llvm/ADT/Statistic.h"
17  #include "llvm/Analysis/AssumptionCache.h"
18  #include "llvm/IR/Dominators.h"
19  #include "llvm/IR/Function.h"
20  #include "llvm/IR/Instructions.h"
21  #include "llvm/Transforms/Utils/PromoteMemToReg.h"
22  #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
23  using namespace llvm;
24  
25  #define DEBUG_TYPE "mem2reg"
26  
27  STATISTIC(NumPromoted, "Number of alloca's promoted");
28  
29  namespace {
30    struct PromotePass : public FunctionPass {
31      static char ID; // Pass identification, replacement for typeid
PromotePass__anonb95b15a40111::PromotePass32      PromotePass() : FunctionPass(ID) {
33        initializePromotePassPass(*PassRegistry::getPassRegistry());
34      }
35  
36      // runOnFunction - To run this pass, first we calculate the alloca
37      // instructions that are safe for promotion, then we promote each one.
38      //
39      bool runOnFunction(Function &F) override;
40  
getAnalysisUsage__anonb95b15a40111::PromotePass41      void getAnalysisUsage(AnalysisUsage &AU) const override {
42        AU.addRequired<AssumptionCacheTracker>();
43        AU.addRequired<DominatorTreeWrapperPass>();
44        AU.setPreservesCFG();
45        // This is a cluster of orthogonal Transforms
46        AU.addPreserved<UnifyFunctionExitNodes>();
47        AU.addPreservedID(LowerSwitchID);
48        AU.addPreservedID(LowerInvokePassID);
49      }
50    };
51  }  // end of anonymous namespace
52  
53  char PromotePass::ID = 0;
54  INITIALIZE_PASS_BEGIN(PromotePass, "mem2reg", "Promote Memory to Register",
55                  false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)56  INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
57  INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
58  INITIALIZE_PASS_END(PromotePass, "mem2reg", "Promote Memory to Register",
59                  false, false)
60  
61  bool PromotePass::runOnFunction(Function &F) {
62    std::vector<AllocaInst*> Allocas;
63  
64    BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
65  
66    if (F.hasFnAttribute(Attribute::OptimizeNone))
67      return false;
68  
69    bool Changed  = false;
70  
71    DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
72    AssumptionCache &AC =
73        getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
74  
75    while (1) {
76      Allocas.clear();
77  
78      // Find allocas that are safe to promote, by looking at all instructions in
79      // the entry node
80      for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
81        if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
82          if (isAllocaPromotable(AI))
83            Allocas.push_back(AI);
84  
85      if (Allocas.empty()) break;
86  
87      PromoteMemToReg(Allocas, DT, nullptr, &AC);
88      NumPromoted += Allocas.size();
89      Changed = true;
90    }
91  
92    return Changed;
93  }
94  
95  // createPromoteMemoryToRegister - Provide an entry point to create this pass.
96  //
createPromoteMemoryToRegisterPass()97  FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
98    return new PromotePass();
99  }
100