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