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97 lines
3.5 KiB
C++
97 lines
3.5 KiB
C++
//===-- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. -===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a MachineFunctionPass that inserts the appropriate
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// XRay instrumentation instructions. We look for XRay-specific attributes
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// on the function to determine whether we should insert the replacement
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// operations.
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//
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//===---------------------------------------------------------------------===//
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#include "llvm/CodeGen/Analysis.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Support/TargetRegistry.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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namespace {
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struct XRayInstrumentation : public MachineFunctionPass {
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static char ID;
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XRayInstrumentation() : MachineFunctionPass(ID) {
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initializeXRayInstrumentationPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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};
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}
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bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
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auto &F = *MF.getFunction();
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auto InstrAttr = F.getFnAttribute("function-instrument");
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bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
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InstrAttr.isStringAttribute() &&
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InstrAttr.getValueAsString() == "xray-always";
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Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
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unsigned XRayThreshold = 0;
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if (!AlwaysInstrument) {
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if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
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return false; // XRay threshold attribute not found.
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if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
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return false; // Invalid value for threshold.
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if (F.size() < XRayThreshold)
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return false; // Function is too small.
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}
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// FIXME: Do the loop triviality analysis here or in an earlier pass.
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// First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
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// MachineFunction.
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auto &FirstMBB = *MF.begin();
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auto &FirstMI = *FirstMBB.begin();
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auto *TII = MF.getSubtarget().getInstrInfo();
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BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
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// Then we look for *all* terminators and returns, then replace those with
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// PATCHABLE_RET instructions.
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SmallVector<MachineInstr *, 4> Terminators;
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for (auto &MBB : MF) {
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for (auto &T : MBB.terminators()) {
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// FIXME: Handle tail calls here too?
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if (T.isReturn() && T.getOpcode() == TII->getReturnOpcode()) {
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// Replace return instructions with:
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// PATCHABLE_RET <Opcode>, <Operand>...
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auto MIB = BuildMI(MBB, T, T.getDebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_RET))
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.addImm(T.getOpcode());
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for (auto &MO : T.operands())
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MIB.addOperand(MO);
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Terminators.push_back(&T);
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break;
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}
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}
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}
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for (auto &I : Terminators)
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I->eraseFromParent();
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return true;
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}
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char XRayInstrumentation::ID = 0;
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char &llvm::XRayInstrumentationID = XRayInstrumentation::ID;
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INITIALIZE_PASS(XRayInstrumentation, "xray-instrumentation", "Insert XRay ops",
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false, false)
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