1 //===-- NVPTXPeephole.cpp - NVPTX Peephole Optimiztions -------------------===//
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 // In NVPTX, NVPTXFrameLowering will emit following instruction at the beginning
11 // of a MachineFunction.
12 //
13 // mov %SPL, %depot
14 // cvta.local %SP, %SPL
15 //
16 // Because Frame Index is a generic address and alloca can only return generic
17 // pointer, without this pass the instructions producing alloca'ed address will
18 // be based on %SP. NVPTXLowerAlloca tends to help replace store and load on
19 // this address with their .local versions, but this may introduce a lot of
20 // cvta.to.local instructions. Performance can be improved if we avoid casting
21 // address back and forth and directly calculate local address based on %SPL.
22 // This peephole pass optimizes these cases, for example
23 //
24 // It will transform the following pattern
25 // %vreg0<def> = LEA_ADDRi64 %VRFrame, 4
26 // %vreg1<def> = cvta_to_local_yes_64 %vreg0
27 //
28 // into
29 // %vreg1<def> = LEA_ADDRi64 %VRFrameLocal, 4
30 //
31 // %VRFrameLocal is the virtual register name of %SPL
32 //
33 //===----------------------------------------------------------------------===//
34
35 #include "NVPTX.h"
36 #include "llvm/CodeGen/MachineFunctionPass.h"
37 #include "llvm/CodeGen/MachineInstrBuilder.h"
38 #include "llvm/CodeGen/MachineRegisterInfo.h"
39 #include "llvm/Target/TargetRegisterInfo.h"
40 #include "llvm/Target/TargetInstrInfo.h"
41
42 using namespace llvm;
43
44 #define DEBUG_TYPE "nvptx-peephole"
45
46 namespace llvm {
47 void initializeNVPTXPeepholePass(PassRegistry &);
48 }
49
50 namespace {
51 struct NVPTXPeephole : public MachineFunctionPass {
52 public:
53 static char ID;
NVPTXPeephole__anon739b03090111::NVPTXPeephole54 NVPTXPeephole() : MachineFunctionPass(ID) {
55 initializeNVPTXPeepholePass(*PassRegistry::getPassRegistry());
56 }
57
58 bool runOnMachineFunction(MachineFunction &MF) override;
59
getPassName__anon739b03090111::NVPTXPeephole60 const char *getPassName() const override {
61 return "NVPTX optimize redundant cvta.to.local instruction";
62 }
63
getAnalysisUsage__anon739b03090111::NVPTXPeephole64 void getAnalysisUsage(AnalysisUsage &AU) const override {
65 MachineFunctionPass::getAnalysisUsage(AU);
66 }
67 };
68 }
69
70 char NVPTXPeephole::ID = 0;
71
72 INITIALIZE_PASS(NVPTXPeephole, "nvptx-peephole", "NVPTX Peephole", false, false)
73
isCVTAToLocalCombinationCandidate(MachineInstr & Root)74 static bool isCVTAToLocalCombinationCandidate(MachineInstr &Root) {
75 auto &MBB = *Root.getParent();
76 auto &MF = *MBB.getParent();
77 // Check current instruction is cvta.to.local
78 if (Root.getOpcode() != NVPTX::cvta_to_local_yes_64 &&
79 Root.getOpcode() != NVPTX::cvta_to_local_yes)
80 return false;
81
82 auto &Op = Root.getOperand(1);
83 const auto &MRI = MF.getRegInfo();
84 MachineInstr *GenericAddrDef = nullptr;
85 if (Op.isReg() && TargetRegisterInfo::isVirtualRegister(Op.getReg())) {
86 GenericAddrDef = MRI.getUniqueVRegDef(Op.getReg());
87 }
88
89 // Check the register operand is uniquely defined by LEA_ADDRi instruction
90 if (!GenericAddrDef || GenericAddrDef->getParent() != &MBB ||
91 (GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi64 &&
92 GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi)) {
93 return false;
94 }
95
96 // Check the LEA_ADDRi operand is Frame index
97 auto &BaseAddrOp = GenericAddrDef->getOperand(1);
98 if (BaseAddrOp.isReg() && BaseAddrOp.getReg() == NVPTX::VRFrame) {
99 return true;
100 }
101
102 return false;
103 }
104
CombineCVTAToLocal(MachineInstr & Root)105 static void CombineCVTAToLocal(MachineInstr &Root) {
106 auto &MBB = *Root.getParent();
107 auto &MF = *MBB.getParent();
108 const auto &MRI = MF.getRegInfo();
109 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
110 auto &Prev = *MRI.getUniqueVRegDef(Root.getOperand(1).getReg());
111
112 MachineInstrBuilder MIB =
113 BuildMI(MF, Root.getDebugLoc(), TII->get(Prev.getOpcode()),
114 Root.getOperand(0).getReg())
115 .addReg(NVPTX::VRFrameLocal)
116 .addOperand(Prev.getOperand(2));
117
118 MBB.insert((MachineBasicBlock::iterator)&Root, MIB);
119
120 // Check if MRI has only one non dbg use, which is Root
121 if (MRI.hasOneNonDBGUse(Prev.getOperand(0).getReg())) {
122 Prev.eraseFromParentAndMarkDBGValuesForRemoval();
123 }
124 Root.eraseFromParentAndMarkDBGValuesForRemoval();
125 }
126
runOnMachineFunction(MachineFunction & MF)127 bool NVPTXPeephole::runOnMachineFunction(MachineFunction &MF) {
128 bool Changed = false;
129 // Loop over all of the basic blocks.
130 for (auto &MBB : MF) {
131 // Traverse the basic block.
132 auto BlockIter = MBB.begin();
133
134 while (BlockIter != MBB.end()) {
135 auto &MI = *BlockIter++;
136 if (isCVTAToLocalCombinationCandidate(MI)) {
137 CombineCVTAToLocal(MI);
138 Changed = true;
139 }
140 } // Instruction
141 } // Basic Block
142
143 // Remove unnecessary %VRFrame = cvta.local %VRFrameLocal
144 const auto &MRI = MF.getRegInfo();
145 if (MRI.use_empty(NVPTX::VRFrame)) {
146 if (auto MI = MRI.getUniqueVRegDef(NVPTX::VRFrame)) {
147 MI->eraseFromParentAndMarkDBGValuesForRemoval();
148 }
149 }
150
151 return Changed;
152 }
153
createNVPTXPeephole()154 MachineFunctionPass *llvm::createNVPTXPeephole() { return new NVPTXPeephole(); }
155