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/Utils/Mem2Reg.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/Scalar.h"
22#include "llvm/Transforms/Utils/PromoteMemToReg.h"
23#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
24using namespace llvm;
25
26#define DEBUG_TYPE "mem2reg"
27
28STATISTIC(NumPromoted, "Number of alloca's promoted");
29
30static bool promoteMemoryToRegister(Function &F, DominatorTree &DT,
31                                    AssumptionCache &AC) {
32  std::vector<AllocaInst *> Allocas;
33  BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
34  bool Changed = false;
35
36  while (1) {
37    Allocas.clear();
38
39    // Find allocas that are safe to promote, by looking at all instructions in
40    // the entry node
41    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
42      if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
43        if (isAllocaPromotable(AI))
44          Allocas.push_back(AI);
45
46    if (Allocas.empty())
47      break;
48
49    PromoteMemToReg(Allocas, DT, nullptr, &AC);
50    NumPromoted += Allocas.size();
51    Changed = true;
52  }
53  return Changed;
54}
55
56PreservedAnalyses PromotePass::run(Function &F, AnalysisManager<Function> &AM) {
57  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
58  auto &AC = AM.getResult<AssumptionAnalysis>(F);
59  if (!promoteMemoryToRegister(F, DT, AC))
60    return PreservedAnalyses::all();
61
62  // FIXME: This should also 'preserve the CFG'.
63  return PreservedAnalyses::none();
64}
65
66namespace {
67struct PromoteLegacyPass : public FunctionPass {
68  static char ID; // Pass identification, replacement for typeid
69  PromoteLegacyPass() : FunctionPass(ID) {
70    initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
71  }
72
73  // runOnFunction - To run this pass, first we calculate the alloca
74  // instructions that are safe for promotion, then we promote each one.
75  //
76  bool runOnFunction(Function &F) override {
77    if (skipFunction(F))
78      return false;
79
80    DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
81    AssumptionCache &AC =
82        getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
83    return promoteMemoryToRegister(F, DT, AC);
84  }
85
86  void getAnalysisUsage(AnalysisUsage &AU) const override {
87    AU.addRequired<AssumptionCacheTracker>();
88    AU.addRequired<DominatorTreeWrapperPass>();
89    AU.setPreservesCFG();
90  }
91  };
92}  // end of anonymous namespace
93
94char PromoteLegacyPass::ID = 0;
95INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
96                                                    "Register",
97                      false, false)
98INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
99INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
100INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
101                    false, false)
102
103// createPromoteMemoryToRegister - Provide an entry point to create this pass.
104//
105FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
106  return new PromoteLegacyPass();
107}
108