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/AssumptionTracker.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
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<AssumptionTracker>();
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)
56 INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
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   bool Changed  = false;
67 
68   DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
69   AssumptionTracker *AT = &getAnalysis<AssumptionTracker>();
70 
71   while (1) {
72     Allocas.clear();
73 
74     // Find allocas that are safe to promote, by looking at all instructions in
75     // the entry node
76     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
77       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
78         if (isAllocaPromotable(AI))
79           Allocas.push_back(AI);
80 
81     if (Allocas.empty()) break;
82 
83     PromoteMemToReg(Allocas, DT, nullptr, AT);
84     NumPromoted += Allocas.size();
85     Changed = true;
86   }
87 
88   return Changed;
89 }
90 
91 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
92 //
93 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
94   return new PromotePass();
95 }
96