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