1 //===-- BPFRegisterInfo.cpp - BPF Register Information ----------*- 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 // This file contains the BPF implementation of the TargetRegisterInfo class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "BPFRegisterInfo.h"
15 #include "BPF.h"
16 #include "BPFSubtarget.h"
17 #include "llvm/CodeGen/MachineFrameInfo.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineInstrBuilder.h"
20 #include "llvm/CodeGen/RegisterScavenging.h"
21 #include "llvm/CodeGen/TargetFrameLowering.h"
22 #include "llvm/CodeGen/TargetInstrInfo.h"
23 #include "llvm/IR/DiagnosticInfo.h"
24 #include "llvm/Support/ErrorHandling.h"
25 
26 #define GET_REGINFO_TARGET_DESC
27 #include "BPFGenRegisterInfo.inc"
28 using namespace llvm;
29 
30 BPFRegisterInfo::BPFRegisterInfo()
31     : BPFGenRegisterInfo(BPF::R0) {}
32 
33 const MCPhysReg *
34 BPFRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
35   return CSR_SaveList;
36 }
37 
38 BitVector BPFRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
39   BitVector Reserved(getNumRegs());
40   markSuperRegs(Reserved, BPF::W10); // [W|R]10 is read only frame pointer
41   markSuperRegs(Reserved, BPF::W11); // [W|R]11 is pseudo stack pointer
42   return Reserved;
43 }
44 
45 static void WarnSize(int Offset, MachineFunction &MF, DebugLoc& DL)
46 {
47   if (Offset <= -512) {
48       const Function &F = MF.getFunction();
49       DiagnosticInfoUnsupported DiagStackSize(F,
50           "Looks like the BPF stack limit of 512 bytes is exceeded. "
51           "Please move large on stack variables into BPF per-cpu array map.\n",
52           DL);
53       F.getContext().diagnose(DiagStackSize);
54   }
55 }
56 
57 void BPFRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
58                                           int SPAdj, unsigned FIOperandNum,
59                                           RegScavenger *RS) const {
60   assert(SPAdj == 0 && "Unexpected");
61 
62   unsigned i = 0;
63   MachineInstr &MI = *II;
64   MachineBasicBlock &MBB = *MI.getParent();
65   MachineFunction &MF = *MBB.getParent();
66   DebugLoc DL = MI.getDebugLoc();
67 
68   if (!DL)
69     /* try harder to get some debug loc */
70     for (auto &I : MBB)
71       if (I.getDebugLoc()) {
72         DL = I.getDebugLoc();
73         break;
74       }
75 
76   while (!MI.getOperand(i).isFI()) {
77     ++i;
78     assert(i < MI.getNumOperands() && "Instr doesn't have FrameIndex operand!");
79   }
80 
81   unsigned FrameReg = getFrameRegister(MF);
82   int FrameIndex = MI.getOperand(i).getIndex();
83   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
84 
85   if (MI.getOpcode() == BPF::MOV_rr) {
86     int Offset = MF.getFrameInfo().getObjectOffset(FrameIndex);
87 
88     WarnSize(Offset, MF, DL);
89     MI.getOperand(i).ChangeToRegister(FrameReg, false);
90     unsigned reg = MI.getOperand(i - 1).getReg();
91     BuildMI(MBB, ++II, DL, TII.get(BPF::ADD_ri), reg)
92         .addReg(reg)
93         .addImm(Offset);
94     return;
95   }
96 
97   int Offset = MF.getFrameInfo().getObjectOffset(FrameIndex) +
98                MI.getOperand(i + 1).getImm();
99 
100   if (!isInt<32>(Offset))
101     llvm_unreachable("bug in frame offset");
102 
103   WarnSize(Offset, MF, DL);
104 
105   if (MI.getOpcode() == BPF::FI_ri) {
106     // architecture does not really support FI_ri, replace it with
107     //    MOV_rr <target_reg>, frame_reg
108     //    ADD_ri <target_reg>, imm
109     unsigned reg = MI.getOperand(i - 1).getReg();
110 
111     BuildMI(MBB, ++II, DL, TII.get(BPF::MOV_rr), reg)
112         .addReg(FrameReg);
113     BuildMI(MBB, II, DL, TII.get(BPF::ADD_ri), reg)
114         .addReg(reg)
115         .addImm(Offset);
116 
117     // Remove FI_ri instruction
118     MI.eraseFromParent();
119   } else {
120     MI.getOperand(i).ChangeToRegister(FrameReg, false);
121     MI.getOperand(i + 1).ChangeToImmediate(Offset);
122   }
123 }
124 
125 unsigned BPFRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
126   return BPF::R10;
127 }
128