//===- ArmSMEToSCF.cpp - Convert ArmSME to SCF dialect ----------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements lowering of ArmSME operations to SCF.
//
//===----------------------------------------------------------------------===//
#include "mlir/Conversion/ArmSMEToSCF/ArmSMEToSCF.h"

#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/ArmSME/IR/ArmSME.h"
#include "mlir/Dialect/ArmSME/Utils/Utils.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/DialectConversion.h"

namespace mlir {
#define GEN_PASS_DEF_CONVERTARMSMETOSCF
#include "mlir/Conversion/Passes.h.inc"
} // namespace mlir

using namespace mlir;

namespace {
/// Adjusts `indices` as follows for a given tile slice and returns them in
/// `outIndices`:
///   rank 1: (indices[0] + (tileSliceIndex * tileSliceNumElts))
///   rank 2: (indices[0] + tileSliceIndex, indices[1])
void getMemrefIndices(ValueRange indices, unsigned rank, Value tileSliceIndex,
                      Value tileSliceNumElts,
                      SmallVectorImpl<Value> &outIndices, Location loc,
                      PatternRewriter &rewriter) {
  assert((rank == 1 || rank == 2) && "memref has unexpected rank!");

  auto tileSliceOffset = tileSliceIndex;
  if (rank == 1)
    tileSliceOffset =
        rewriter.create<arith::MulIOp>(loc, tileSliceOffset, tileSliceNumElts);

  auto baseIndexPlusTileSliceOffset =
      rewriter.create<arith::AddIOp>(loc, indices[0], tileSliceOffset);
  outIndices.push_back(baseIndexPlusTileSliceOffset);

  if (rank == 2)
    outIndices.push_back(indices[1]);
}

/// Lower `arm_sme.tile_load` to a loop over the tile slices and load each slice
/// using `arm_sme.load_tile_slice`.
///
///  BEFORE:
///  ```mlir
///  %tile = arm_sme.tile_load %src[%c0, %c0] :
///    memref<?x?xi32>, vector<[4]x[4]xi32>
///  ```
///
///  AFTER:
///  ```mlir
///  %tile_id = arm_sme.get_tile_id : i32
///  %tile = arm_sme.cast_tile_to_vector %tile_id : i32 to vector<[4]x[4]xi32>
///  %vscale = vector.vscale
///  %c0 = arith.constant 0 : index
///  %c1 = arith.constant 1 : index
///  %min_svl_s = arith.constant 4 : index
///  %svl_s = arith.muli %min_svl_s, %vscale : index
///  scf.for %tile_slice_idx = %c0 to %svl_s step %c1 {
///    %tile_update = arm_sme.load_tile_slice %src[%tile_slice_idx],
///      %tile, %tile_slice_idx : memref<?x?xi32>, vector<[4]x[4]xi32>
///  }
///  ```
struct TileLoadOpConversion : public OpRewritePattern<arm_sme::TileLoadOp> {
  using OpRewritePattern<arm_sme::TileLoadOp>::OpRewritePattern;

  LogicalResult matchAndRewrite(arm_sme::TileLoadOp tileLoadOp,
                                PatternRewriter &rewriter) const override {
    OpBuilder::InsertionGuard g(rewriter);
    auto loc = tileLoadOp.getLoc();
    auto tileType = tileLoadOp.getVectorType();
    auto tileElementType = tileType.getElementType();
    unsigned tileElementWidth = tileElementType.getIntOrFloatBitWidth();

    // Create 'arm_sme.get_tile' op.
    auto tileId = rewriter.create<arm_sme::GetTileID>(
        loc, rewriter.getIntegerType(tileElementWidth));

    // Create `arm_sme.cast_tile_to_vector` to cast tile ID to a vector type to
    // use as input tile to 'arm_sme.load_tile_slice' ops.
    auto tile =
        rewriter.create<arm_sme::CastTileToVector>(loc, tileType, tileId);

    // Create a loop that loads each ZA tile slice from memory.
    auto step = rewriter.create<arith::ConstantIndexOp>(loc, 1);
    auto minTileSlices = rewriter.create<arith::ConstantIndexOp>(
        loc, arm_sme::getSMETileSliceMinNumElts(tileElementType));
    auto vscale =
        rewriter.create<vector::VectorScaleOp>(loc, rewriter.getIndexType());
    auto lowerBound = rewriter.create<arith::ConstantIndexOp>(loc, 0);
    // This describes both the number of ZA tile slices and the number of
    // elements in a vector of SVL bits for a given element type (SVL_B, SVL_H,
    // ..., SVL_Q).
    auto numTileSlices =
        rewriter.create<arith::MulIOp>(loc, minTileSlices, vscale);
    auto forOp =
        rewriter.create<scf::ForOp>(loc, lowerBound, numTileSlices, step);

    rewriter.setInsertionPointToStart(forOp.getBody());

    // Create 'arm_sme.load_tile_slice' to load tile slice from memory into
    // tile.
    SmallVector<Value> memrefIndices;
    auto tileSliceIndex = forOp.getInductionVar();
    getMemrefIndices(tileLoadOp.getIndices(),
                     tileLoadOp.getMemRefType().getRank(), tileSliceIndex,
                     numTileSlices, memrefIndices, loc, rewriter);
    rewriter.create<arm_sme::LoadTileSliceOp>(loc, tileType,
                                              tileLoadOp.getBase(), tile,
                                              memrefIndices, tileSliceIndex);

    rewriter.setInsertionPointAfter(forOp);

    // Replace 'arm_sme.tile_load' with the tile.
    rewriter.replaceOp(tileLoadOp, tile);

    return success();
  }
};

/// Lower `arm_sme.tile_store` to a loop over the tile slices and store each
/// slice using `arm_sme.store_tile_slice`.
///
///  BEFORE:
///  ```mlir
///  arm_sme.tile_store %tile, %dest[%c0, %c0]
///    : memref<?x?xi32>, vector<[4]x[4]xi32
///  ```
///
///  AFTER:
///  ```mlir
///  %vscale = vector.vscale
///  %c0 = arith.constant 0 : index
///  %c1 = arith.constant 1 : index
///  %min_svl_s = arith.constant 4 : index
///  %svl_s = arith.muli %min_svl_s, %vscale : index
///  scf.for %tile_slice_idx = %c0 to %svl_s step %c1 {
///    arm_sme.store_tile_slice %tile, %tile_slice_idx, %dest[%tile_slice_idx]
///      : memref<?x?xi32>, vector<[4]x[4]xi32>
///  }
///  ```
struct TileStoreOpConversion : public OpRewritePattern<arm_sme::TileStoreOp> {
  using OpRewritePattern<arm_sme::TileStoreOp>::OpRewritePattern;

  LogicalResult matchAndRewrite(arm_sme::TileStoreOp tileStoreOp,
                                PatternRewriter &rewriter) const override {
    OpBuilder::InsertionGuard g(rewriter);
    auto loc = tileStoreOp.getLoc();
    auto tileType = tileStoreOp.getVectorType();
    auto tileElementType = tileType.getElementType();

    // Create a loop that stores each ZA tile slice from memory.
    auto step = rewriter.create<arith::ConstantIndexOp>(loc, 1);
    auto minTileSlices = rewriter.create<arith::ConstantIndexOp>(
        loc, arm_sme::getSMETileSliceMinNumElts(tileElementType));
    auto vscale =
        rewriter.create<vector::VectorScaleOp>(loc, rewriter.getIndexType());
    auto lowerBound = rewriter.create<arith::ConstantIndexOp>(loc, 0);
    // This describes both the number of ZA tile slices and the number of
    // elements in a vector of SVL bits for a given element type (SVL_B, SVL_H,
    // ..., SVL_Q).
    auto numTileSlices =
        rewriter.create<arith::MulIOp>(loc, minTileSlices, vscale);
    auto forOp =
        rewriter.create<scf::ForOp>(loc, lowerBound, numTileSlices, step);

    rewriter.setInsertionPointToStart(forOp.getBody());

    SmallVector<Value> memrefIndices;
    auto tileSliceIndex = forOp.getInductionVar();
    getMemrefIndices(tileStoreOp.getIndices(),
                     tileStoreOp.getMemRefType().getRank(), tileSliceIndex,
                     numTileSlices, memrefIndices, loc, rewriter);
    rewriter.replaceOpWithNewOp<arm_sme::StoreTileSliceOp>(
        tileStoreOp, tileStoreOp.getValueToStore(), tileSliceIndex,
        tileStoreOp.getBase(), memrefIndices);

    return success();
  }
};

} // namespace

void mlir::populateArmSMEToSCFConversionPatterns(RewritePatternSet &patterns) {
  patterns.add<TileLoadOpConversion, TileStoreOpConversion>(
      patterns.getContext());
}

namespace {

struct ConvertArmSMEToSCFPass
    : public impl::ConvertArmSMEToSCFBase<ConvertArmSMEToSCFPass> {
  void runOnOperation() override {
    RewritePatternSet patterns(&getContext());
    ConversionTarget target(getContext());
    populateArmSMEToSCFConversionPatterns(patterns);
    target.addLegalDialect<arm_sme::ArmSMEDialect, vector::VectorDialect,
                           arith::ArithDialect, scf::SCFDialect>();
    target.addIllegalOp<arm_sme::TileLoadOp, arm_sme::TileStoreOp>();
    if (failed(applyPartialConversion(getOperation(), target,
                                      std::move(patterns))))
      signalPassFailure();
  }
};

} // namespace

std::unique_ptr<Pass> mlir::createConvertArmSMEToSCFPass() {
  return std::make_unique<ConvertArmSMEToSCFPass>();
}