1 //===-- LVLGen.cpp - LVL instruction generator ----------------------------===//
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 #include "VE.h"
10 #include "VESubtarget.h"
11 #include "llvm/CodeGen/MachineFunctionPass.h"
12 #include "llvm/CodeGen/MachineInstrBuilder.h"
13 #include "llvm/CodeGen/MachineRegisterInfo.h"
14 #include "llvm/CodeGen/TargetInstrInfo.h"
15 #include "llvm/Target/TargetMachine.h"
16 
17 using namespace llvm;
18 
19 #define DEBUG_TYPE "lvl-gen"
20 
21 namespace {
22 struct LVLGen : public MachineFunctionPass {
23   const TargetInstrInfo *TII;
24   const TargetRegisterInfo *TRI;
25 
26   static char ID;
27   LVLGen() : MachineFunctionPass(ID) {}
28   bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
29   bool runOnMachineFunction(MachineFunction &F) override;
30 
31   unsigned getVL(const MachineInstr &MI);
32   int getVLIndex(unsigned Opcode);
33 };
34 char LVLGen::ID = 0;
35 
36 } // end of anonymous namespace
37 
38 FunctionPass *llvm::createLVLGenPass() { return new LVLGen; }
39 
40 int LVLGen::getVLIndex(unsigned Opcode) {
41   const MCInstrDesc &MCID = TII->get(Opcode);
42 
43   // If an instruction has VLIndex information, return it.
44   if (HAS_VLINDEX(MCID.TSFlags))
45     return GET_VLINDEX(MCID.TSFlags);
46 
47   return -1;
48 }
49 
50 // returns a register holding a vector length. NoRegister is returned when
51 // this MI does not have a vector length.
52 unsigned LVLGen::getVL(const MachineInstr &MI) {
53   int Index = getVLIndex(MI.getOpcode());
54   if (Index >= 0)
55     return MI.getOperand(Index).getReg();
56 
57   return VE::NoRegister;
58 }
59 
60 bool LVLGen::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
61 #define RegName(no)                                                            \
62   (MBB.getParent()->getSubtarget<VESubtarget>().getRegisterInfo()->getName(no))
63 
64   bool Changed = false;
65   bool HasRegForVL = false;
66   unsigned RegForVL;
67 
68   for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end();) {
69     MachineBasicBlock::iterator MI = I;
70 
71     // Check whether MI uses a vector length operand.  If so, we prepare for VL
72     // register.  We would like to reuse VL register as much as possible.  We
73     // also would like to keep the number of LEA instructions as fewer as
74     // possible.  Therefore, we use a regular scalar register to hold immediate
75     // values to load VL register.  And try to reuse identical scalar registers
76     // to avoid new LVLr instructions as much as possible.
77     unsigned Reg = getVL(*MI);
78     if (Reg != VE::NoRegister) {
79       LLVM_DEBUG(dbgs() << "Vector instruction found: ");
80       LLVM_DEBUG(MI->dump());
81       LLVM_DEBUG(dbgs() << "Vector length is " << RegName(Reg) << ". ");
82       LLVM_DEBUG(dbgs() << "Current VL is "
83                         << (HasRegForVL ? RegName(RegForVL) : "unknown")
84                         << ". ");
85 
86       if (!HasRegForVL || RegForVL != Reg) {
87         // Use VL, but a different value in a different scalar register.
88         // So, generate new LVL instruction just before the current instruction.
89         LLVM_DEBUG(dbgs() << "Generate a LVL instruction to load "
90                           << RegName(Reg) << ".\n");
91         BuildMI(MBB, I, MI->getDebugLoc(), TII->get(VE::LVLr)).addReg(Reg);
92         HasRegForVL = true;
93         RegForVL = Reg;
94         Changed = true;
95       } else {
96         LLVM_DEBUG(dbgs() << "Reuse current VL.\n");
97       }
98     }
99     // Check the update of a given scalar register holding an immediate value
100     // for VL register.  Also, a call doesn't preserve VL register.
101     if (HasRegForVL) {
102       if (MI->definesRegister(RegForVL, TRI) ||
103           MI->modifiesRegister(RegForVL, TRI) ||
104           MI->killsRegister(RegForVL, TRI) || MI->isCall()) {
105         // The latest VL is needed to be updated, so disable HasRegForVL.
106         LLVM_DEBUG(dbgs() << RegName(RegForVL) << " is needed to be updated: ");
107         LLVM_DEBUG(MI->dump());
108         HasRegForVL = false;
109       }
110     }
111 
112     ++I;
113   }
114   return Changed;
115 }
116 
117 bool LVLGen::runOnMachineFunction(MachineFunction &F) {
118   LLVM_DEBUG(dbgs() << "********** Begin LVLGen **********\n");
119   LLVM_DEBUG(dbgs() << "********** Function: " << F.getName() << '\n');
120   LLVM_DEBUG(F.dump());
121 
122   bool Changed = false;
123 
124   const VESubtarget &Subtarget = F.getSubtarget<VESubtarget>();
125   TII = Subtarget.getInstrInfo();
126   TRI = Subtarget.getRegisterInfo();
127 
128   for (MachineBasicBlock &MBB : F)
129     Changed |= runOnMachineBasicBlock(MBB);
130 
131   if (Changed) {
132     LLVM_DEBUG(dbgs() << "\n");
133     LLVM_DEBUG(F.dump());
134   }
135   LLVM_DEBUG(dbgs() << "********** End LVLGen **********\n");
136   return Changed;
137 }
138