Thumb2ITBlockPass.cpp revision 205407 
1//===-- Thumb2ITBlockPass.cpp - Insert Thumb IT blocks ----------*- C++ -*-===//
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#define DEBUG_TYPE "thumb2-it"
11#include "ARM.h"
12#include "ARMMachineFunctionInfo.h"
13#include "Thumb2InstrInfo.h"
14#include "llvm/CodeGen/MachineInstr.h"
15#include "llvm/CodeGen/MachineInstrBuilder.h"
16#include "llvm/CodeGen/MachineFunctionPass.h"
17#include "llvm/ADT/Statistic.h"
18using namespace llvm;
19
20STATISTIC(NumITs,     "Number of IT blocks inserted");
21
22namespace {
23  struct Thumb2ITBlockPass : public MachineFunctionPass {
24    static char ID;
25    Thumb2ITBlockPass() : MachineFunctionPass(&ID) {}
26
27    const Thumb2InstrInfo *TII;
28    ARMFunctionInfo *AFI;
29
30    virtual bool runOnMachineFunction(MachineFunction &Fn);
31
32    virtual const char *getPassName() const {
33      return "Thumb IT blocks insertion pass";
34    }
35
36  private:
37    bool InsertITBlocks(MachineBasicBlock &MBB);
38  };
39  char Thumb2ITBlockPass::ID = 0;
40}
41
42static ARMCC::CondCodes getPredicate(const MachineInstr *MI, unsigned &PredReg){
43  unsigned Opc = MI->getOpcode();
44  if (Opc == ARM::tBcc || Opc == ARM::t2Bcc)
45    return ARMCC::AL;
46  return llvm::getInstrPredicate(MI, PredReg);
47}
48
49bool Thumb2ITBlockPass::InsertITBlocks(MachineBasicBlock &MBB) {
50  bool Modified = false;
51
52  MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
53  while (MBBI != E) {
54    MachineInstr *MI = &*MBBI;
55    DebugLoc dl = MI->getDebugLoc();
56    unsigned PredReg = 0;
57    ARMCC::CondCodes CC = getPredicate(MI, PredReg);
58
59    if (CC == ARMCC::AL) {
60      ++MBBI;
61      continue;
62    }
63
64    // Insert an IT instruction.
65    MachineInstrBuilder MIB = BuildMI(MBB, MBBI, dl, TII->get(ARM::t2IT))
66      .addImm(CC);
67    ++MBBI;
68
69    // Finalize IT mask.
70    ARMCC::CondCodes OCC = ARMCC::getOppositeCondition(CC);
71    unsigned Mask = 0, Pos = 3;
72    // Branches, including tricky ones like LDM_RET, need to end an IT
73    // block so check the instruction we just put in the block.
74    while (MBBI != E && Pos &&
75           (!MI->getDesc().isBranch() && !MI->getDesc().isReturn())) {
76      MachineInstr *NMI = &*MBBI;
77      MI = NMI;
78      DebugLoc ndl = NMI->getDebugLoc();
79      unsigned NPredReg = 0;
80      ARMCC::CondCodes NCC = getPredicate(NMI, NPredReg);
81      if (NCC == CC || NCC == OCC)
82        Mask |= (NCC & 1) << Pos;
83      else
84        break;
85      --Pos;
86      ++MBBI;
87    }
88    Mask |= (1 << Pos);
89    // Tag along (firstcond[0] << 4) with the mask.
90    Mask |= (CC & 1) << 4;
91    MIB.addImm(Mask);
92    Modified = true;
93    ++NumITs;
94  }
95
96  return Modified;
97}
98
99bool Thumb2ITBlockPass::runOnMachineFunction(MachineFunction &Fn) {
100  const TargetMachine &TM = Fn.getTarget();
101  AFI = Fn.getInfo<ARMFunctionInfo>();
102  TII = static_cast<const Thumb2InstrInfo*>(TM.getInstrInfo());
103
104  if (!AFI->isThumbFunction())
105    return false;
106
107  bool Modified = false;
108  for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
109       ++MFI) {
110    MachineBasicBlock &MBB = *MFI;
111    Modified |= InsertITBlocks(MBB);
112  }
113
114  return Modified;
115}
116
117/// createThumb2ITBlockPass - Returns an instance of the Thumb2 IT blocks
118/// insertion pass.
119FunctionPass *llvm::createThumb2ITBlockPass() {
120  return new Thumb2ITBlockPass();
121}
122