1 //===- NVPTXProxyRegErasure.cpp - NVPTX Proxy Register Instruction Erasure -==//
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 // The pass is needed to remove ProxyReg instructions and restore related
11 // registers. The instructions were needed at instruction selection stage to
12 // make sure that callseq_end nodes won't be removed as "dead nodes". This can
13 // happen when we expand instructions into libcalls and the call site doesn't
14 // care about the libcall chain. Call site cares about data flow only, and the
15 // latest data flow node happens to be before callseq_end. Therefore the node
16 // becomes dangling and "dead". The ProxyReg acts like an additional data flow
17 // node *after* the callseq_end in the chain and ensures that everything will be
18 // preserved.
19 //
20 //===----------------------------------------------------------------------===//
21 
22 #include "NVPTX.h"
23 #include "llvm/CodeGen/MachineFunctionPass.h"
24 #include "llvm/CodeGen/MachineInstrBuilder.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/TargetInstrInfo.h"
27 #include "llvm/CodeGen/TargetRegisterInfo.h"
28 
29 using namespace llvm;
30 
31 namespace llvm {
32 void initializeNVPTXProxyRegErasurePass(PassRegistry &);
33 }
34 
35 namespace {
36 
37 struct NVPTXProxyRegErasure : public MachineFunctionPass {
38 public:
39   static char ID;
40   NVPTXProxyRegErasure() : MachineFunctionPass(ID) {
41     initializeNVPTXProxyRegErasurePass(*PassRegistry::getPassRegistry());
42   }
43 
44   bool runOnMachineFunction(MachineFunction &MF) override;
45 
46   StringRef getPassName() const override {
47     return "NVPTX Proxy Register Instruction Erasure";
48   }
49 
50   void getAnalysisUsage(AnalysisUsage &AU) const override {
51     MachineFunctionPass::getAnalysisUsage(AU);
52   }
53 
54 private:
55   void replaceMachineInstructionUsage(MachineFunction &MF, MachineInstr &MI);
56 
57   void replaceRegisterUsage(MachineInstr &Instr, MachineOperand &From,
58                             MachineOperand &To);
59 };
60 
61 } // namespace
62 
63 char NVPTXProxyRegErasure::ID = 0;
64 
65 INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure", "NVPTX ProxyReg Erasure", false, false)
66 
67 bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
68   SmallVector<MachineInstr *, 16> RemoveList;
69 
70   for (auto &BB : MF) {
71     for (auto &MI : BB) {
72       switch (MI.getOpcode()) {
73       case NVPTX::ProxyRegI1:
74       case NVPTX::ProxyRegI16:
75       case NVPTX::ProxyRegI32:
76       case NVPTX::ProxyRegI64:
77       case NVPTX::ProxyRegF16:
78       case NVPTX::ProxyRegF16x2:
79       case NVPTX::ProxyRegF32:
80       case NVPTX::ProxyRegF64:
81         replaceMachineInstructionUsage(MF, MI);
82         RemoveList.push_back(&MI);
83         break;
84       }
85     }
86   }
87 
88   for (auto *MI : RemoveList) {
89     MI->eraseFromParent();
90   }
91 
92   return !RemoveList.empty();
93 }
94 
95 void NVPTXProxyRegErasure::replaceMachineInstructionUsage(MachineFunction &MF,
96                                                           MachineInstr &MI) {
97   auto &InOp = *MI.uses().begin();
98   auto &OutOp = *MI.defs().begin();
99 
100   assert(InOp.isReg() && "ProxyReg input operand should be a register.");
101   assert(OutOp.isReg() && "ProxyReg output operand should be a register.");
102 
103   for (auto &BB : MF) {
104     for (auto &I : BB) {
105       replaceRegisterUsage(I, OutOp, InOp);
106     }
107   }
108 }
109 
110 void NVPTXProxyRegErasure::replaceRegisterUsage(MachineInstr &Instr,
111                                                 MachineOperand &From,
112                                                 MachineOperand &To) {
113   for (auto &Op : Instr.uses()) {
114     if (Op.isReg() && Op.getReg() == From.getReg()) {
115       Op.setReg(To.getReg());
116     }
117   }
118 }
119 
120 MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {
121   return new NVPTXProxyRegErasure();
122 }
123