1 //===- TailDuplication.cpp - Duplicate blocks into predecessors' tails ----===//
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 /// \file This pass duplicates basic blocks ending in unconditional branches
10 /// into the tails of their predecessors, using the TailDuplicator utility
11 /// class.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Analysis/ProfileSummaryInfo.h"
16 #include "llvm/CodeGen/LazyMachineBlockFrequencyInfo.h"
17 #include "llvm/CodeGen/MBFIWrapper.h"
18 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/TailDuplicator.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Pass.h"
24 #include "llvm/PassRegistry.h"
25 
26 using namespace llvm;
27 
28 #define DEBUG_TYPE "tailduplication"
29 
30 namespace {
31 
32 class TailDuplicateBase : public MachineFunctionPass {
33   TailDuplicator Duplicator;
34   std::unique_ptr<MBFIWrapper> MBFIW;
35   bool PreRegAlloc;
36 public:
37   TailDuplicateBase(char &PassID, bool PreRegAlloc)
38     : MachineFunctionPass(PassID), PreRegAlloc(PreRegAlloc) {}
39 
40   bool runOnMachineFunction(MachineFunction &MF) override;
41 
42   void getAnalysisUsage(AnalysisUsage &AU) const override {
43     AU.addRequired<MachineBranchProbabilityInfo>();
44     AU.addRequired<LazyMachineBlockFrequencyInfoPass>();
45     AU.addRequired<ProfileSummaryInfoWrapperPass>();
46     MachineFunctionPass::getAnalysisUsage(AU);
47   }
48 };
49 
50 class TailDuplicate : public TailDuplicateBase {
51 public:
52   static char ID;
53   TailDuplicate() : TailDuplicateBase(ID, false) {
54     initializeTailDuplicatePass(*PassRegistry::getPassRegistry());
55   }
56 };
57 
58 class EarlyTailDuplicate : public TailDuplicateBase {
59 public:
60   static char ID;
61   EarlyTailDuplicate() : TailDuplicateBase(ID, true) {
62     initializeEarlyTailDuplicatePass(*PassRegistry::getPassRegistry());
63   }
64 
65   MachineFunctionProperties getClearedProperties() const override {
66     return MachineFunctionProperties()
67       .set(MachineFunctionProperties::Property::NoPHIs);
68   }
69 };
70 
71 } // end anonymous namespace
72 
73 char TailDuplicate::ID;
74 char EarlyTailDuplicate::ID;
75 
76 char &llvm::TailDuplicateID = TailDuplicate::ID;
77 char &llvm::EarlyTailDuplicateID = EarlyTailDuplicate::ID;
78 
79 INITIALIZE_PASS(TailDuplicate, DEBUG_TYPE, "Tail Duplication", false, false)
80 INITIALIZE_PASS(EarlyTailDuplicate, "early-tailduplication",
81                 "Early Tail Duplication", false, false)
82 
83 bool TailDuplicateBase::runOnMachineFunction(MachineFunction &MF) {
84   if (skipFunction(MF.getFunction()))
85     return false;
86 
87   auto MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
88   auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
89   auto *MBFI = (PSI && PSI->hasProfileSummary()) ?
90                &getAnalysis<LazyMachineBlockFrequencyInfoPass>().getBFI() :
91                nullptr;
92   if (MBFI)
93     MBFIW = std::make_unique<MBFIWrapper>(*MBFI);
94   Duplicator.initMF(MF, PreRegAlloc, MBPI, MBFI ? MBFIW.get() : nullptr, PSI,
95                     /*LayoutMode=*/false);
96 
97   bool MadeChange = false;
98   while (Duplicator.tailDuplicateBlocks())
99     MadeChange = true;
100 
101   return MadeChange;
102 }
103