//===-- MathToLibm.cpp - conversion from Math to libm calls ---------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "mlir/Conversion/MathToLibm/MathToLibm.h"

#include "../PassDetail.h"
#include "mlir/Dialect/Math/IR/Math.h"
#include "mlir/Dialect/StandardOps/IR/Ops.h"
#include "mlir/Dialect/Vector/VectorOps.h"
#include "mlir/IR/BuiltinDialect.h"
#include "mlir/IR/PatternMatch.h"

using namespace mlir;

namespace {
// Pattern to convert vector operations to scalar operations. This is needed as
// libm calls require scalars.
template <typename Op>
struct VecOpToScalarOp : public OpRewritePattern<Op> {
public:
  using OpRewritePattern<Op>::OpRewritePattern;

  LogicalResult matchAndRewrite(Op op, PatternRewriter &rewriter) const final;
};
// Pattern to convert scalar math operations to calls to libm functions.
// Additionally the libm function signatures are declared.
template <typename Op>
struct ScalarOpToLibmCall : public OpRewritePattern<Op> {
public:
  using OpRewritePattern<Op>::OpRewritePattern;
  ScalarOpToLibmCall<Op>(MLIRContext *context, StringRef floatFunc,
                         StringRef doubleFunc, PatternBenefit benefit)
      : OpRewritePattern<Op>(context, benefit), floatFunc(floatFunc),
        doubleFunc(doubleFunc){};

  LogicalResult matchAndRewrite(Op op, PatternRewriter &rewriter) const final;

private:
  std::string floatFunc, doubleFunc;
};
} // namespace

template <typename Op>
LogicalResult
VecOpToScalarOp<Op>::matchAndRewrite(Op op, PatternRewriter &rewriter) const {
  auto opType = op.getType();
  auto loc = op.getLoc();
  auto vecType = opType.template dyn_cast<VectorType>();

  if (!vecType)
    return failure();
  if (!vecType.hasRank())
    return failure();
  auto shape = vecType.getShape();
  // TODO: support multidimensional vectors
  if (shape.size() != 1)
    return failure();

  Value result = rewriter.create<ConstantOp>(
      loc, DenseElementsAttr::get(
               vecType, FloatAttr::get(vecType.getElementType(), 0.0)));
  for (auto i = 0; i < shape.front(); ++i) {
    SmallVector<Value> operands;
    for (auto input : op->getOperands())
      operands.push_back(
          rewriter.create<vector::ExtractElementOp>(loc, input, i));
    Value scalarOp =
        rewriter.create<Op>(loc, vecType.getElementType(), operands);
    result = rewriter.create<vector::InsertElementOp>(loc, scalarOp, result, i);
  }
  rewriter.replaceOp(op, {result});
  return success();
}

template <typename Op>
LogicalResult
ScalarOpToLibmCall<Op>::matchAndRewrite(Op op,
                                        PatternRewriter &rewriter) const {
  auto module = op->template getParentOfType<ModuleOp>();
  auto type = op.getType();
  // TODO: Support Float16 by upcasting to Float32
  if (!type.template isa<Float32Type, Float64Type>())
    return failure();

  auto name = type.getIntOrFloatBitWidth() == 64 ? doubleFunc : floatFunc;
  auto opFunc = module.template lookupSymbol<FuncOp>(name);
  // Forward declare function if it hasn't already been
  if (!opFunc) {
    OpBuilder::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(module.getBody());
    auto opFunctionTy = FunctionType::get(
        rewriter.getContext(), op->getOperandTypes(), op->getResultTypes());
    opFunc =
        rewriter.create<FuncOp>(rewriter.getUnknownLoc(), name, opFunctionTy);
    opFunc.setPrivate();
  }
  assert(opFunc.getType().template cast<FunctionType>().getResults() ==
         op->getResultTypes());
  assert(opFunc.getType().template cast<FunctionType>().getInputs() ==
         op->getOperandTypes());

  rewriter.replaceOpWithNewOp<CallOp>(op, opFunc, op->getOperands());

  return success();
}

void mlir::populateMathToLibmConversionPatterns(RewritePatternSet &patterns,
                                                PatternBenefit benefit) {
  patterns.add<VecOpToScalarOp<math::Atan2Op>, VecOpToScalarOp<math::ExpM1Op>,
               VecOpToScalarOp<math::TanhOp>>(patterns.getContext(), benefit);
  patterns.add<ScalarOpToLibmCall<math::Atan2Op>>(patterns.getContext(),
                                                  "atan2f", "atan2", benefit);
  patterns.add<ScalarOpToLibmCall<math::ExpM1Op>>(patterns.getContext(),
                                                  "expm1f", "expm1", benefit);
  patterns.add<ScalarOpToLibmCall<math::TanhOp>>(patterns.getContext(), "tanhf",
                                                 "tanh", benefit);
}

namespace {
struct ConvertMathToLibmPass
    : public ConvertMathToLibmBase<ConvertMathToLibmPass> {
  void runOnOperation() override;
};
} // namespace

void ConvertMathToLibmPass::runOnOperation() {
  auto module = getOperation();

  RewritePatternSet patterns(&getContext());
  populateMathToLibmConversionPatterns(patterns, /*benefit=*/1);

  ConversionTarget target(getContext());
  target.addLegalDialect<BuiltinDialect, StandardOpsDialect,
                         vector::VectorDialect>();
  target.addIllegalDialect<math::MathDialect>();
  if (failed(applyPartialConversion(module, target, std::move(patterns))))
    signalPassFailure();
}

std::unique_ptr<OperationPass<ModuleOp>> mlir::createConvertMathToLibmPass() {
  return std::make_unique<ConvertMathToLibmPass>();
}
