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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
PromotePass__anona2cd17a20111::PromotePass30     PromotePass() : FunctionPass(ID) {
31       initializePromotePassPass(*PassRegistry::getPassRegistry());
32     }
33 
34     // runOnFunction - To run this pass, first we calculate the alloca
35     // instructions that are safe for promotion, then we promote each one.
36     //
37     virtual bool runOnFunction(Function &F);
38 
getAnalysisUsage__anona2cd17a20111::PromotePass39     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
40       AU.addRequired<DominatorTree>();
41       AU.setPreservesCFG();
42       // This is a cluster of orthogonal Transforms
43       AU.addPreserved<UnifyFunctionExitNodes>();
44       AU.addPreservedID(LowerSwitchID);
45       AU.addPreservedID(LowerInvokePassID);
46     }
47   };
48 }  // end of anonymous namespace
49 
50 char PromotePass::ID = 0;
51 INITIALIZE_PASS_BEGIN(PromotePass, "mem2reg", "Promote Memory to Register",
52                 false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)53 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
54 INITIALIZE_PASS_END(PromotePass, "mem2reg", "Promote Memory to Register",
55                 false, false)
56 
57 bool PromotePass::runOnFunction(Function &F) {
58   std::vector<AllocaInst*> Allocas;
59 
60   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
61 
62   bool Changed  = false;
63 
64   DominatorTree &DT = getAnalysis<DominatorTree>();
65 
66   while (1) {
67     Allocas.clear();
68 
69     // Find allocas that are safe to promote, by looking at all instructions in
70     // the entry node
71     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
72       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
73         if (isAllocaPromotable(AI))
74           Allocas.push_back(AI);
75 
76     if (Allocas.empty()) break;
77 
78     PromoteMemToReg(Allocas, DT);
79     NumPromoted += Allocas.size();
80     Changed = true;
81   }
82 
83   return Changed;
84 }
85 
86 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
87 //
createPromoteMemoryToRegisterPass()88 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
89   return new PromotePass();
90 }
91