1 //===- TailDuplication.cpp - Duplicate blocks into predecessors' tails ----===//
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 duplicates basic blocks ending in unconditional branches into
11 // the tails of their predecessors, using the TailDuplicator utility class.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineFunctionPass.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/CodeGen/TailDuplicator.h"
21 #include "llvm/Pass.h"
22 
23 using namespace llvm;
24 
25 #define DEBUG_TYPE "tailduplication"
26 
27 namespace {
28 
29 /// Perform tail duplication. Delegates to TailDuplicator
30 class TailDuplicatePass : public MachineFunctionPass {
31   TailDuplicator Duplicator;
32 
33 public:
34   static char ID;
35 
36   explicit TailDuplicatePass() : MachineFunctionPass(ID) {}
37 
38   bool runOnMachineFunction(MachineFunction &MF) override;
39 
40   void getAnalysisUsage(AnalysisUsage &AU) const override;
41 };
42 
43 } // end anonymous namespace
44 
45 char TailDuplicatePass::ID = 0;
46 
47 char &llvm::TailDuplicateID = TailDuplicatePass::ID;
48 
49 INITIALIZE_PASS(TailDuplicatePass, DEBUG_TYPE, "Tail Duplication", false, false)
50 
51 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
52   if (skipFunction(MF.getFunction()))
53     return false;
54 
55   auto MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
56 
57   // TODO: Querying isSSA() to determine pre-/post-regalloc is fragile, better
58   // split this into two passes instead.
59   bool PreRegAlloc = MF.getRegInfo().isSSA();
60   Duplicator.initMF(MF, PreRegAlloc, MBPI, /* LayoutMode */ false);
61 
62   bool MadeChange = false;
63   while (Duplicator.tailDuplicateBlocks())
64     MadeChange = true;
65 
66   return MadeChange;
67 }
68 
69 void TailDuplicatePass::getAnalysisUsage(AnalysisUsage &AU) const {
70   AU.addRequired<MachineBranchProbabilityInfo>();
71   MachineFunctionPass::getAnalysisUsage(AU);
72 }
73