StackFrameLayoutAnalysisPass.cpp

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//===-- StackFrameLayoutAnalysisPass.cpp
//------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// StackFrameLayoutAnalysisPass implementation. Outputs information about the
// layout of the stack frame, using the remarks interface. On the CLI it prints
// a textual representation of the stack frame. When possible it prints the
// values that occupy a stack slot using any available debug information. Since
// output is remarks based, it is also available in a machine readable file
// format, such as YAML.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/StackProtector.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/PrintPasses.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/raw_ostream.h"
 
#include <sstream>
 
using namespace llvm;
 
#define DEBUG_TYPE "stack-frame-layout"
 
namespace {
 
/// StackFrameLayoutAnalysisPass - This is a pass to dump the stack frame of a
/// MachineFunction.
///
struct StackFrameLayoutAnalysisPass : public MachineFunctionPass {
  using SlotDbgMap = SmallDenseMap<int, SetVector<const DILocalVariable *>>;
  static char ID;
 
  enum SlotType {
    Spill,          // a Spill slot
    StackProtector, // Stack Protector slot
    Variable,       // a slot used to store a local data (could be a tmp)
    Invalid         // It's an error for a slot to have this type
  };
 
  struct SlotData {
    int Slot;
    int Size;
    int Align;
    int Offset;
    SlotType SlotTy;
    bool Scalable;
 
    SlotData(const MachineFrameInfo &MFI, const int ValOffset, const int Idx)
        : Slot(Idx), Size(MFI.getObjectSize(Idx)),
          Align(MFI.getObjectAlign(Idx).value()),
          Offset(MFI.getObjectOffset(Idx) - ValOffset), SlotTy(Invalid),
          Scalable(false) {
      Scalable = MFI.getStackID(Idx) == TargetStackID::ScalableVector;
      if (MFI.isSpillSlotObjectIndex(Idx))
        SlotTy = SlotType::Spill;
      else if (Idx == MFI.getStackProtectorIndex())
        SlotTy = SlotType::StackProtector;
      else
        SlotTy = SlotType::Variable;
    }
 
    // We use this to sort in reverse order, so that the layout is displayed
    // correctly. Scalable slots are sorted to the end of the list.
    bool operator<(const SlotData &Rhs) const {
      return std::make_tuple(!Scalable, Offset) >
             std::make_tuple(!Rhs.Scalable, Rhs.Offset);
    }
  };
 
  StackFrameLayoutAnalysisPass() : MachineFunctionPass(ID) {}
 
  StringRef getPassName() const override {
    return "Stack Frame Layout Analysis";
  }
 
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
    MachineFunctionPass::getAnalysisUsage(AU);
    AU.addRequired<MachineOptimizationRemarkEmitterPass>();
  }
 
  bool runOnMachineFunction(MachineFunction &MF) override {
    // TODO: We should implement a similar filter for remarks:
    //   -Rpass-func-filter=<regex>
    if (!isFunctionInPrintList(MF.getName()))
      return false;
 
    LLVMContext &Ctx = MF.getFunction().getContext();
    if (!Ctx.getDiagHandlerPtr()->isAnalysisRemarkEnabled(DEBUG_TYPE))
      return false;
 
    MachineOptimizationRemarkAnalysis Rem(DEBUG_TYPE, "StackLayout",
                                          MF.getFunction().getSubprogram(),
                                          &MF.front());
    Rem << ("\nFunction: " + MF.getName()).str();
    emitStackFrameLayoutRemarks(MF, Rem);
    getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE().emit(Rem);
    return false;
  }
 
  std::string getTypeString(SlotType Ty) {
    switch (Ty) {
    case SlotType::Spill:
      return "Spill";
    case SlotType::StackProtector:
      return "Protector";
    case SlotType::Variable:
      return "Variable";
    default:
      llvm_unreachable("bad slot type for stack layout");
    }
  }
 
  void emitStackSlotRemark(const MachineFunction &MF, const SlotData &D,
                           MachineOptimizationRemarkAnalysis &Rem) {
    // To make it easy to understand the stack layout from the CLI, we want to
    // print each slot like the following:
    //
    //   Offset: [SP+8], Type: Spill, Align: 8, Size: 16
    //       foo @ /path/to/file.c:25
    //       bar @ /path/to/file.c:35
    //
    // Which prints the size, alignment, and offset from the SP at function
    // entry.
    //
    // But we also want the machine readable remarks data to be nicely
    // organized. So we print some additional data as strings for the CLI
    // output, but maintain more structured data for the YAML.
    //
    // For example we store the Offset in YAML as:
    //    ...
    //    - Offset: -8
    //
    // But we print it to the CLI as
    //   Offset: [SP-8]
 
    // Negative offsets will print a leading `-`, so only add `+`
    std::string Prefix =
        formatv("\nOffset: [SP{0}", (D.Offset < 0) ? "" : "+").str();
    Rem << Prefix << ore::NV("Offset", D.Offset)
        << "], Type: " << ore::NV("Type", getTypeString(D.SlotTy))
        << ", Align: " << ore::NV("Align", D.Align)
        << ", Size: " << ore::NV("Size", ElementCount::get(D.Size, D.Scalable));
  }
 
  void emitSourceLocRemark(const MachineFunction &MF, const DILocalVariable *N,
                           MachineOptimizationRemarkAnalysis &Rem) {
    std::string Loc =
        formatv("{0} @ {1}:{2}", N->getName(), N->getFilename(), N->getLine())
            .str();
    Rem << "\n    " << ore::NV("DataLoc", Loc);
  }
 
  void emitStackFrameLayoutRemarks(MachineFunction &MF,
                                   MachineOptimizationRemarkAnalysis &Rem) {
    const MachineFrameInfo &MFI = MF.getFrameInfo();
    if (!MFI.hasStackObjects())
      return;
 
    // ValOffset is the offset to the local area from the SP at function entry.
    // To display the true offset from SP, we need to subtract ValOffset from
    // MFI's ObjectOffset.
    const TargetFrameLowering *FI = MF.getSubtarget().getFrameLowering();
    const int ValOffset = (FI ? FI->getOffsetOfLocalArea() : 0);
 
    LLVM_DEBUG(dbgs() << "getStackProtectorIndex =="
                      << MFI.getStackProtectorIndex() << "\n");
 
    std::vector<SlotData> SlotInfo;
 
    const unsigned int NumObj = MFI.getNumObjects();
    SlotInfo.reserve(NumObj);
    // initialize slot info
    for (int Idx = MFI.getObjectIndexBegin(), EndIdx = MFI.getObjectIndexEnd();
         Idx != EndIdx; ++Idx) {
      if (MFI.isDeadObjectIndex(Idx))
        continue;
      SlotInfo.emplace_back(MFI, ValOffset, Idx);
    }
 
    // sort the ordering, to match the actual layout in memory
    llvm::sort(SlotInfo);
 
    SlotDbgMap SlotMap = genSlotDbgMapping(MF);
 
    for (const SlotData &Info : SlotInfo) {
      emitStackSlotRemark(MF, Info, Rem);
      for (const DILocalVariable *N : SlotMap[Info.Slot])
        emitSourceLocRemark(MF, N, Rem);
    }
  }
 
  // We need to generate a mapping of slots to the values that are stored to
  // them. This information is lost by the time we need to print out the frame,
  // so we reconstruct it here by walking the CFG, and generating the mapping.
  SlotDbgMap genSlotDbgMapping(MachineFunction &MF) {
    SlotDbgMap SlotDebugMap;
 
    // add variables to the map
    for (MachineFunction::VariableDbgInfo &DI :
         MF.getInStackSlotVariableDbgInfo())
      SlotDebugMap[DI.getStackSlot()].insert(DI.Var);
 
    // Then add all the spills that have debug data
    for (MachineBasicBlock &MBB : MF) {
      for (MachineInstr &MI : MBB) {
        for (MachineMemOperand *MO : MI.memoperands()) {
          if (!MO->isStore())
            continue;
          auto *FI = dyn_cast_or_null<FixedStackPseudoSourceValue>(
              MO->getPseudoValue());
          if (!FI)
            continue;
          int FrameIdx = FI->getFrameIndex();
          SmallVector<MachineInstr *> Dbg;
          MI.collectDebugValues(Dbg);
 
          for (MachineInstr *MI : Dbg)
            SlotDebugMap[FrameIdx].insert(MI->getDebugVariable());
        }
      }
    }
 
    return SlotDebugMap;
  }
};
 
char StackFrameLayoutAnalysisPass::ID = 0;
} // namespace
 
char &llvm::StackFrameLayoutAnalysisPassID = StackFrameLayoutAnalysisPass::ID;
INITIALIZE_PASS(StackFrameLayoutAnalysisPass, "stack-frame-layout",
                "Stack Frame Layout", false, false)
 
namespace llvm {
/// Returns a newly-created StackFrameLayout pass.
MachineFunctionPass *createStackFrameLayoutAnalysisPass() {
  return new StackFrameLayoutAnalysisPass();
}
 
} // namespace llvm