1 //===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass is a simple pass wrapper around the PromoteMemToReg function call
10 // exposed by the Utils library.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Utils/Mem2Reg.h"
15 #include "llvm/ADT/Statistic.h"
16 #include "llvm/Analysis/AssumptionCache.h"
17 #include "llvm/IR/BasicBlock.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/PassManager.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Support/Casting.h"
25 #include "llvm/Transforms/Utils.h"
26 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
27 #include <vector>
28 
29 using namespace llvm;
30 
31 #define DEBUG_TYPE "mem2reg"
32 
33 STATISTIC(NumPromoted, "Number of alloca's promoted");
34 
35 static bool promoteMemoryToRegister(Function &F, DominatorTree &DT,
36                                     AssumptionCache &AC) {
37   std::vector<AllocaInst *> Allocas;
38   BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
39   bool Changed = false;
40 
41   while (true) {
42     Allocas.clear();
43 
44     // Find allocas that are safe to promote, by looking at all instructions in
45     // the entry node
46     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
47       if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
48         if (isAllocaPromotable(AI))
49           Allocas.push_back(AI);
50 
51     if (Allocas.empty())
52       break;
53 
54     PromoteMemToReg(Allocas, DT, &AC);
55     NumPromoted += Allocas.size();
56     Changed = true;
57   }
58   return Changed;
59 }
60 
61 PreservedAnalyses PromotePass::run(Function &F, FunctionAnalysisManager &AM) {
62   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
63   auto &AC = AM.getResult<AssumptionAnalysis>(F);
64   if (!promoteMemoryToRegister(F, DT, AC))
65     return PreservedAnalyses::all();
66 
67   PreservedAnalyses PA;
68   PA.preserveSet<CFGAnalyses>();
69   return PA;
70 }
71 
72 namespace {
73 
74 struct PromoteLegacyPass : public FunctionPass {
75   // Pass identification, replacement for typeid
76   static char ID;
77 
78   PromoteLegacyPass() : FunctionPass(ID) {
79     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
80   }
81 
82   // runOnFunction - To run this pass, first we calculate the alloca
83   // instructions that are safe for promotion, then we promote each one.
84   bool runOnFunction(Function &F) override {
85     if (skipFunction(F))
86       return false;
87 
88     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
89     AssumptionCache &AC =
90         getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
91     return promoteMemoryToRegister(F, DT, AC);
92   }
93 
94   void getAnalysisUsage(AnalysisUsage &AU) const override {
95     AU.addRequired<AssumptionCacheTracker>();
96     AU.addRequired<DominatorTreeWrapperPass>();
97     AU.setPreservesCFG();
98   }
99 };
100 
101 } // end anonymous namespace
102 
103 char PromoteLegacyPass::ID = 0;
104 
105 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
106                                                     "Register",
107                       false, false)
108 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
109 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
110 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
111                     false, false)
112 
113 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
114 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
115   return new PromoteLegacyPass();
116 }
117