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"
23using namespace llvm;
24
25#define DEBUG_TYPE "mem2reg"
26
27STATISTIC(NumPromoted, "Number of alloca's promoted");
28
29namespace {
30  struct PromotePass : public FunctionPass {
31    static char ID; // Pass identification, replacement for typeid
32    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
41    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
53char PromotePass::ID = 0;
54INITIALIZE_PASS_BEGIN(PromotePass, "mem2reg", "Promote Memory to Register",
55                false, false)
56INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
57INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
58INITIALIZE_PASS_END(PromotePass, "mem2reg", "Promote Memory to Register",
59                false, false)
60
61bool 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//
97FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
98  return new PromotePass();
99}
100