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