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//===-- RISCVISelDAGToDAG.cpp - A dag to dag inst selector for RISCV ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines an instruction selector for the RISCV target.
//
//===----------------------------------------------------------------------===//
#include "RISCV.h"
#include "MCTargetDesc/RISCVMCTargetDesc.h"
#include "RISCVTargetMachine.h"
#include "llvm/CodeGen/SelectionDAGISel.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "riscv-isel"
// RISCV-specific code to select RISCV machine instructions for
// SelectionDAG operations.
namespace {
class RISCVDAGToDAGISel final : public SelectionDAGISel {
const RISCVSubtarget *Subtarget;
public:
explicit RISCVDAGToDAGISel(RISCVTargetMachine &TargetMachine)
: SelectionDAGISel(TargetMachine) {}
StringRef getPassName() const override {
return "RISCV DAG->DAG Pattern Instruction Selection";
}
bool runOnMachineFunction(MachineFunction &MF) override {
Subtarget = &MF.getSubtarget<RISCVSubtarget>();
return SelectionDAGISel::runOnMachineFunction(MF);
}
void Select(SDNode *Node) override;
// Include the pieces autogenerated from the target description.
#include "RISCVGenDAGISel.inc"
};
}
void RISCVDAGToDAGISel::Select(SDNode *Node) {
unsigned Opcode = Node->getOpcode();
MVT XLenVT = Subtarget->getXLenVT();
// Dump information about the Node being selected.
DEBUG(dbgs() << "Selecting: "; Node->dump(CurDAG); dbgs() << "\n");
// If we have a custom node, we have already selected
if (Node->isMachineOpcode()) {
DEBUG(dbgs() << "== "; Node->dump(CurDAG); dbgs() << "\n");
Node->setNodeId(-1);
return;
}
// Instruction Selection not handled by the auto-generated tablegen selection
// should be handled here.
EVT VT = Node->getValueType(0);
switch (Opcode) {
case ISD::Constant:
if (VT == XLenVT) {
ConstantSDNode *ConstNode = cast<ConstantSDNode>(Node);
// Materialize zero constants as copies from X0. This allows the coalescer
// to propagate these into other instructions.
if (ConstNode->isNullValue()) {
SDValue New = CurDAG->getCopyFromReg(CurDAG->getEntryNode(),
SDLoc(Node), RISCV::X0, XLenVT);
return ReplaceNode(Node, New.getNode());
}
}
break;
default:
break;
}
// Select the default instruction.
SelectCode(Node);
}
// This pass converts a legalized DAG into a RISCV-specific DAG, ready
// for instruction scheduling.
FunctionPass *llvm::createRISCVISelDag(RISCVTargetMachine &TM) {
return new RISCVDAGToDAGISel(TM);
}
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