1 //===--- SIDebuggerInsertNops.cpp - Inserts nops for debugger usage -------===//
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 /// \file
11 /// Inserts one nop instruction for each high level source statement for
12 /// debugger usage.
13 ///
14 /// Tools, such as a debugger, need to pause execution based on user input (i.e.
15 /// breakpoint). In order to do this, one nop instruction is inserted before the
16 /// first isa instruction of each high level source statement. Further, the
17 /// debugger may replace nop instructions with trap instructions based on user
18 /// input.
19 //
20 //===----------------------------------------------------------------------===//
21 
22 #include "AMDGPUSubtarget.h"
23 #include "SIInstrInfo.h"
24 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
25 #include "llvm/ADT/DenseSet.h"
26 #include "llvm/CodeGen/MachineFunction.h"
27 #include "llvm/CodeGen/MachineFunctionPass.h"
28 #include "llvm/CodeGen/MachineInstrBuilder.h"
29 #include "llvm/CodeGen/MachineModuleInfo.h"
30 using namespace llvm;
31 
32 #define DEBUG_TYPE "si-debugger-insert-nops"
33 #define PASS_NAME "SI Debugger Insert Nops"
34 
35 namespace {
36 
37 class SIDebuggerInsertNops : public MachineFunctionPass {
38 public:
39   static char ID;
40 
41   SIDebuggerInsertNops() : MachineFunctionPass(ID) { }
42   StringRef getPassName() const override { return PASS_NAME; }
43 
44   void getAnalysisUsage(AnalysisUsage &AU) const override {
45     AU.setPreservesCFG();
46     MachineFunctionPass::getAnalysisUsage(AU);
47   }
48 
49   bool runOnMachineFunction(MachineFunction &MF) override;
50 };
51 
52 } // anonymous namespace
53 
54 INITIALIZE_PASS(SIDebuggerInsertNops, DEBUG_TYPE, PASS_NAME, false, false)
55 
56 char SIDebuggerInsertNops::ID = 0;
57 char &llvm::SIDebuggerInsertNopsID = SIDebuggerInsertNops::ID;
58 
59 FunctionPass *llvm::createSIDebuggerInsertNopsPass() {
60   return new SIDebuggerInsertNops();
61 }
62 
63 bool SIDebuggerInsertNops::runOnMachineFunction(MachineFunction &MF) {
64   // Skip this pass if "amdgpu-debugger-insert-nops" attribute was not
65   // specified.
66   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
67   if (!ST.debuggerInsertNops())
68     return false;
69 
70   // Skip machine functions without debug info.
71   if (!MF.getMMI().hasDebugInfo())
72     return false;
73 
74   // Target instruction info.
75   const SIInstrInfo *TII = ST.getInstrInfo();
76 
77   // Set containing line numbers that have nop inserted.
78   DenseSet<unsigned> NopInserted;
79 
80   for (auto &MBB : MF) {
81     for (auto MI = MBB.begin(); MI != MBB.end(); ++MI) {
82       // Skip debug instructions and instructions without location.
83       if (MI->isDebugInstr() || !MI->getDebugLoc())
84         continue;
85 
86       // Insert nop instruction if line number does not have nop inserted.
87       auto DL = MI->getDebugLoc();
88       if (NopInserted.find(DL.getLine()) == NopInserted.end()) {
89         BuildMI(MBB, *MI, DL, TII->get(AMDGPU::S_NOP))
90           .addImm(0);
91         NopInserted.insert(DL.getLine());
92       }
93     }
94   }
95 
96   return true;
97 }
98