1 //===-- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. -===//
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 implements a MachineFunctionPass that inserts the appropriate
11 // XRay instrumentation instructions. We look for XRay-specific attributes
12 // on the function to determine whether we should insert the replacement
13 // operations.
14 //
15 //===---------------------------------------------------------------------===//
16
17 #include "llvm/CodeGen/Analysis.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/Passes.h"
22 #include "llvm/Support/TargetRegistry.h"
23 #include "llvm/Target/TargetInstrInfo.h"
24 #include "llvm/Target/TargetSubtargetInfo.h"
25
26 using namespace llvm;
27
28 namespace {
29 struct XRayInstrumentation : public MachineFunctionPass {
30 static char ID;
31
XRayInstrumentation__anon738ad4ed0111::XRayInstrumentation32 XRayInstrumentation() : MachineFunctionPass(ID) {
33 initializeXRayInstrumentationPass(*PassRegistry::getPassRegistry());
34 }
35
36 bool runOnMachineFunction(MachineFunction &MF) override;
37 };
38 }
39
runOnMachineFunction(MachineFunction & MF)40 bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
41 auto &F = *MF.getFunction();
42 auto InstrAttr = F.getFnAttribute("function-instrument");
43 bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
44 InstrAttr.isStringAttribute() &&
45 InstrAttr.getValueAsString() == "xray-always";
46 Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
47 unsigned XRayThreshold = 0;
48 if (!AlwaysInstrument) {
49 if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
50 return false; // XRay threshold attribute not found.
51 if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
52 return false; // Invalid value for threshold.
53 if (F.size() < XRayThreshold)
54 return false; // Function is too small.
55 }
56
57 // FIXME: Do the loop triviality analysis here or in an earlier pass.
58
59 // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
60 // MachineFunction.
61 auto &FirstMBB = *MF.begin();
62 auto &FirstMI = *FirstMBB.begin();
63 auto *TII = MF.getSubtarget().getInstrInfo();
64 BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
65 TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
66
67 // Then we look for *all* terminators and returns, then replace those with
68 // PATCHABLE_RET instructions.
69 SmallVector<MachineInstr *, 4> Terminators;
70 for (auto &MBB : MF) {
71 for (auto &T : MBB.terminators()) {
72 // FIXME: Handle tail calls here too?
73 if (T.isReturn() && T.getOpcode() == TII->getReturnOpcode()) {
74 // Replace return instructions with:
75 // PATCHABLE_RET <Opcode>, <Operand>...
76 auto MIB = BuildMI(MBB, T, T.getDebugLoc(),
77 TII->get(TargetOpcode::PATCHABLE_RET))
78 .addImm(T.getOpcode());
79 for (auto &MO : T.operands())
80 MIB.addOperand(MO);
81 Terminators.push_back(&T);
82 break;
83 }
84 }
85 }
86
87 for (auto &I : Terminators)
88 I->eraseFromParent();
89
90 return true;
91 }
92
93 char XRayInstrumentation::ID = 0;
94 char &llvm::XRayInstrumentationID = XRayInstrumentation::ID;
95 INITIALIZE_PASS(XRayInstrumentation, "xray-instrumentation", "Insert XRay ops",
96 false, false)
97