llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

//- WebAssemblyISelDAGToDAG.cpp - A dag to dag inst selector for WebAssembly -//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief This file defines an instruction selector for the WebAssembly target.
///
//===----------------------------------------------------------------------===//

#include "WebAssembly.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssemblyTargetMachine.h"
#include "llvm/CodeGen/SelectionDAGISel.h"
#include "llvm/IR/Function.h" // To access function attributes.
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

#define DEBUG_TYPE "wasm-isel"

//===--------------------------------------------------------------------===//
/// WebAssembly-specific code to select WebAssembly machine instructions for
/// SelectionDAG operations.
///
namespace {
class WebAssemblyDAGToDAGISel final : public SelectionDAGISel {
  /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
  /// right decision when generating code for different targets.
  const WebAssemblySubtarget *Subtarget;

  bool ForCodeSize;

public:
  WebAssemblyDAGToDAGISel(WebAssemblyTargetMachine &tm,
                          CodeGenOpt::Level OptLevel)
      : SelectionDAGISel(tm, OptLevel), Subtarget(nullptr), ForCodeSize(false) {
  }

  const char *getPassName() const override {
    return "WebAssembly Instruction Selection";
  }

  bool runOnMachineFunction(MachineFunction &MF) override {
    ForCodeSize =
        MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize) ||
        MF.getFunction()->hasFnAttribute(Attribute::MinSize);
    Subtarget = &MF.getSubtarget<WebAssemblySubtarget>();
    return SelectionDAGISel::runOnMachineFunction(MF);
  }

  SDNode *Select(SDNode *Node) override;

  bool SelectInlineAsmMemoryOperand(const SDValue &Op, unsigned ConstraintID,
                                    std::vector<SDValue> &OutOps) override;

// Include the pieces autogenerated from the target description.
#include "WebAssemblyGenDAGISel.inc"

private:
  // add select functions here...
};
} // end anonymous namespace

SDNode *WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
  // Dump information about the Node being selected.
  DEBUG(errs() << "Selecting: ");
  DEBUG(Node->dump(CurDAG));
  DEBUG(errs() << "\n");

  // If we have a custom node, we already have selected!
  if (Node->isMachineOpcode()) {
    DEBUG(errs() << "== "; Node->dump(CurDAG); errs() << "\n");
    Node->setNodeId(-1);
    return nullptr;
  }

  // Few custom selection stuff.
  SDNode *ResNode = nullptr;
  EVT VT = Node->getValueType(0);

  switch (Node->getOpcode()) {
  default:
    break;
    // FIXME: Implement WebAssembly-specific selection.
    (void)VT;
  }

  // Select the default instruction.
  ResNode = SelectCode(Node);

  DEBUG(errs() << "=> ");
  if (ResNode == nullptr || ResNode == Node)
    DEBUG(Node->dump(CurDAG));
  else
    DEBUG(ResNode->dump(CurDAG));
  DEBUG(errs() << "\n");

  return ResNode;
}

bool WebAssemblyDAGToDAGISel::SelectInlineAsmMemoryOperand(
    const SDValue &Op, unsigned ConstraintID, std::vector<SDValue> &OutOps) {
  switch (ConstraintID) {
  case InlineAsm::Constraint_i:
  case InlineAsm::Constraint_m:
    // We just support simple memory operands that just have a single address
    // operand and need no special handling.
    OutOps.push_back(Op);
    return false;
  default:
    break;
  }

  return true;
}

/// This pass converts a legalized DAG into a WebAssembly-specific DAG, ready
/// for instruction scheduling.
FunctionPass *llvm::createWebAssemblyISelDag(WebAssemblyTargetMachine &TM,
                                             CodeGenOpt::Level OptLevel) {
  return new WebAssemblyDAGToDAGISel(TM, OptLevel);
}