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fix fft rev diff rule #176

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fix fft rev diff rule #176

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3309771
try fix fft rev diff rule
mofeing Nov 29, 2024
d274ec9
fix typo
mofeing Nov 29, 2024
e4bef24
fix typo
mofeing Nov 29, 2024
8872da9
Merge branch 'main' into mofeing/issue170
mofeing Dec 4, 2024
cac8f69
correct impl
wsmoses Dec 16, 2024
890800b
fixup
wsmoses Dec 17, 2024
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60 changes: 52 additions & 8 deletions src/enzyme_ad/jax/Implementations/HLODerivatives.td
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Original file line number Diff line number Diff line change
Expand Up @@ -681,12 +681,51 @@ def FftLength : GlobalExpr</*needsprimal*/0, /*needsshadow*/0, [{

def FftMultiplier : GlobalExpr</*needsprimal*/0, /*needsshadow*/0, [{
auto op_type = op->getResult(0).getType().cast<RankedTensorType>();
auto lengths = op.getFftLength();
auto lengths = op.getFftLengthAttr().getValues<int64_t>();
auto N = std::accumulate(lengths.begin(), lengths.end(), llvm::APInt(64, 1, true), std::multiplies{}).getSExtValue();

auto ret_constant = builder.create<ConstantOp>(op.getLoc(), builder.getDenseI64ArrayAttr(ArrayRef<int64_t>({N})));
auto ret_broadcast = builder.create<BroadcastInDimOp>(op.getLoc(), op_type.clone(op_type.getShape(), builder.getI64Type()), ret_constant, builder.getI64VectorAttr(op_type.getShape()));
builder.create<ConvertOp>(op.getLoc(), op->getResult(0).getType(), ret_broadcast);
double value = N;
switch (op.getFftType()) {
case FftType::FFT:
break;
case FftType::IFFT:
value = 1 / value;
break;
case FftType::RFFT:
value /= 2;
break;
case FftType::IRFFT:
value = 2 / value;
break;
}
auto resTy = op->getResult(0).getType().cast<RankedTensorType>();
mlir::Value ret_constant = builder.create<ConstantOp>(op.getLoc(), SplatElementsAttr::get(
resTy, FloatAttr::get(resTy.getElementType(), value)));

if (op.getFftType() == FftType::RFFT || op.getFftType() == FftType::IRFFT) {
auto RT = RankedTensorType::get({1}, resTy.getElementType());
auto zero_constant = builder.create<ConstantOp>(op.getLoc(), SplatElementsAttr::get(
RT, FloatAttr::get(resTy.getElementType(), 0)));
auto end_constant = builder.create<ConstantOp>(op.getLoc(), SplatElementsAttr::get(
RT, FloatAttr::get(resTy.getElementType(), lengths[lengths.size()-1]-1)));

auto RT64 = RankedTensorType::get({1}, builder.getIntegerType(64));

Value start[] = {
builder.create<stablehlo::ConstantOp>(op.getLoc(), SplatElementsAttr::get(RT64, rewriter.getI64IntegerAttr(0)))
};
Value end[] = {
builder.create<stablehlo::ConstantOp>(op.getLoc(), SplatElementsAttr::get(RT64, rewriter.getI64IntegerAttr(lengths.size()-1)))
};
ret_constant = builder.create<stablehlo::DynamicUpdateSliceOp>(op.getLoc(), resTy, ret_constant, zero_constant, start);
ret_constant = builder.create<stablehlo::DynamicUpdateSliceOp>(op.getLoc(), resTy, ret_constant, end_constant, end);
}
ret_constant;
}]>;

def FftIsIRFFT : GlobalExpr</*needsprimal*/0, /*needsshadow*/0, [{
auto cond = op.getFftType() == FftType::IRFFT;
builder.create<ConstantOp>(op.getLoc(), builder.getDenseBoolArrayAttr(ArrayRef<bool>({cond})));
}]>;

// Derivative rules
Expand Down Expand Up @@ -785,12 +824,17 @@ def : HLODerivative<"ExpOp", (Op $x), [(CheckedMul (DiffeRet), (Exp $x))]>;

def : HLODerivative<"Expm1Op", (Op $x), [(CheckedMul (DiffeRet), (Exp $x))]>;

// TODO fix `rfft` and `irfft` derivatives:
// - `rfft` => divide `DiffeRet` elems by 2 except 1st elem, and last elem if `FftLength` is even
// - `irfft` =>
def : HLODerivative<"FftOp", (Op $x),
[
(Fft (DiffeRet), (FftType), (FftLength)) // TODO maybe we need to conjugate? or inverse fft + multiply by N?
(Mul
(FftMultiplier), // TODO fix this
(Fft
(Select
(FftIsIRFFT), // if IRFFT
(Real (DiffeRet)), // call real(diff)
(DiffeRet),
(FftTypeInverse),
(FftLength))))
],
(Fft (Shadow $x), (FftType), (FftLength))
>;
Expand Down
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