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[WIP][mlir] DenseElementsAttr::reshape(arg): make arg a shape, not a type #149947

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[WIP][mlir] DenseElementsAttr::reshape(arg): make arg a shape, not a type #149947

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cc6aae0
reshape to a new shape not a new type
newling Jul 21, 2025
8035784
remove not unused API
newling Jul 21, 2025
e7613ea
new clone approach for vector types
newling Jul 22, 2025
30d09ac
cosmetics
newling Jul 22, 2025
8a58a68
update toy
newling Jul 22, 2025
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3 changes: 2 additions & 1 deletion mlir/include/mlir/Dialect/Utils/ReshapeOpsUtils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,8 @@ static OpFoldResult foldReshapeOp(ReshapeOpTy reshapeOp,

// Reshape of a constant can be replaced with a new constant.
if (auto elements = dyn_cast_or_null<DenseElementsAttr>(operands.front()))
return elements.reshape(cast<ShapedType>(reshapeOp.getResult().getType()));
return elements.reshape(
cast<ShapedType>(reshapeOp.getResult().getType()).getShape());

// Fold if the producer reshape source has the same shape with at most 1
// dynamic dimension.
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6 changes: 3 additions & 3 deletions mlir/include/mlir/IR/BuiltinAttributes.h
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Expand Up @@ -615,9 +615,9 @@ class DenseElementsAttr : public Attribute {
//===--------------------------------------------------------------------===//

/// Return a new DenseElementsAttr that has the same data as the current
/// attribute, but has been reshaped to 'newType'. The new type must have the
/// same total number of elements as well as element type.
DenseElementsAttr reshape(ShapedType newType);
/// attribute, but has been reshaped to 'newShape'. The new shape must have
/// the same total number of elements.
DenseElementsAttr reshape(ArrayRef<int64_t> newShape);

/// Return a new DenseElementsAttr that has the same data as the current
/// attribute, but with a different shape for a splat type. The new type must
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5 changes: 3 additions & 2 deletions mlir/lib/CAPI/IR/BuiltinAttributes.cpp
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Expand Up @@ -679,8 +679,9 @@ MlirAttribute mlirDenseElementsAttrStringGet(MlirType shapedType,

MlirAttribute mlirDenseElementsAttrReshapeGet(MlirAttribute attr,
MlirType shapedType) {
return wrap(llvm::cast<DenseElementsAttr>(unwrap(attr))
.reshape(llvm::cast<ShapedType>(unwrap(shapedType))));
return wrap(
llvm::cast<DenseElementsAttr>(unwrap(attr))
.reshape(llvm::cast<ShapedType>(unwrap(shapedType)).getShape()));
}

//===----------------------------------------------------------------------===//
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2 changes: 1 addition & 1 deletion mlir/lib/Conversion/ArithToSPIRV/ArithToSPIRV.cpp
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Expand Up @@ -274,7 +274,7 @@ struct ConstantCompositeOpPattern final
if (isa<RankedTensorType>(srcType)) {
dstAttrType = RankedTensorType::get(srcType.getNumElements(),
srcType.getElementType());
dstElementsAttr = dstElementsAttr.reshape(dstAttrType);
dstElementsAttr = dstElementsAttr.reshape(dstAttrType.getShape());
} else {
// TODO: add support for large vectors.
return failure();
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4 changes: 2 additions & 2 deletions mlir/lib/Dialect/Tosa/IR/TosaCanonicalizations.cpp
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Expand Up @@ -1387,7 +1387,7 @@ OpFoldResult ReshapeOp::fold(FoldAdaptor adaptor) {
return {};

return operand.reshape(
llvm::cast<ShapedType>(operand.getType()).clone(shapeVec));
llvm::cast<ShapedType>(operand.getType()).clone(shapeVec).getShape());
}

return {};
Expand Down Expand Up @@ -1546,7 +1546,7 @@ OpFoldResult TransposeOp::fold(FoldAdaptor adaptor) {
llvm::dyn_cast_if_present<DenseElementsAttr>(adaptor.getInput1())) {
if (input.isSplat() && resultTy.hasStaticShape() &&
input.getType().getElementType() == resultTy.getElementType())
return input.reshape(resultTy);
return input.reshape(resultTy.getShape());
}

// Transpose is not the identity transpose.
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2 changes: 1 addition & 1 deletion mlir/lib/Dialect/Tosa/Transforms/TosaReduceTransposes.cpp
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Expand Up @@ -193,7 +193,7 @@ TosaReduceTransposes::transposeDenseAttribute(DenseElementsAttr input,
RankedTensorType::get(newShape, oldType.getElementType());

if (input.isSplat()) {
return input.reshape(newType);
return input.reshape(newType.getShape());
}

auto rawData = input.getRawData();
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4 changes: 2 additions & 2 deletions mlir/lib/Dialect/Vector/IR/VectorOps.cpp
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Expand Up @@ -6000,7 +6000,7 @@ OpFoldResult ShapeCastOp::fold(FoldAdaptor adaptor) {
// shape_cast(constant) -> constant
if (auto splatAttr =
llvm::dyn_cast_if_present<SplatElementsAttr>(adaptor.getSource()))
return splatAttr.reshape(getType());
return splatAttr.reshape(getType().getShape());

// shape_cast(poison) -> poison
if (llvm::dyn_cast_if_present<ub::PoisonAttr>(adaptor.getSource())) {
Expand Down Expand Up @@ -6346,7 +6346,7 @@ OpFoldResult vector::TransposeOp::fold(FoldAdaptor adaptor) {
// Eliminate splat constant transpose ops.
if (auto splat =
llvm::dyn_cast_if_present<SplatElementsAttr>(adaptor.getVector()))
return splat.reshape(getResultVectorType());
return splat.reshape(getResultVectorType().getShape());

// Eliminate poison transpose ops.
if (llvm::dyn_cast_if_present<ub::PoisonAttr>(adaptor.getVector()))
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2 changes: 1 addition & 1 deletion mlir/lib/Dialect/Vector/Transforms/VectorLinearize.cpp
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Expand Up @@ -36,7 +36,7 @@ linearizeConstAttr(Location loc, ConversionPatternRewriter &rewriter,
loc,
"Cannot linearize a constant scalable vector that's not a splat");

return dstElementsAttr.reshape(resType);
return dstElementsAttr.reshape(resType.getShape());
}

if (auto poisonAttr = dyn_cast<ub::PoisonAttr>(value))
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4 changes: 3 additions & 1 deletion mlir/lib/IR/BuiltinAttributes.cpp
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Expand Up @@ -1241,8 +1241,10 @@ ArrayRef<StringRef> DenseElementsAttr::getRawStringData() const {
/// Return a new DenseElementsAttr that has the same data as the current
/// attribute, but has been reshaped to 'newType'. The new type must have the
/// same total number of elements as well as element type.
DenseElementsAttr DenseElementsAttr::reshape(ShapedType newType) {
DenseElementsAttr DenseElementsAttr::reshape(ArrayRef<int64_t> newShape) {

ShapedType curType = getType();
auto newType = curType.cloneWith(newShape, curType.getElementType());
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@MengmSun MengmSun Jul 22, 2025

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I think if result type conversion is intended then we should keep the element type of converted result type and use for subsequent lowering. Clone with newType.getElementType instead of curType.getElementType.

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@MengmSun MengmSun Jul 22, 2025

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Otherwise the converted information like fp8->i8 will lost.
For example,

func.func @canonicalize_extract_shapecast_different_element_type() -> vector<1x192xf8E4M3FN> {
      %0 = arith.constant dense<1.000000e+00> : vector<192xf8E4M3FN>
      %1 = vector.shape_cast %0 : vector<192xf8E4M3FN> to vector<1x192xf8E4M3FN>
      return %1 : vector<1x192xf8E4M3FN>
}

will be converted to as below after -convert-to-llvm -canonicalize="test-convergence"

module {
  llvm.func @canonicalize_extract_shapecast_different_element_type() -> !llvm.array<1 x vector<192xf8E4M3FN>> {
    %0 = llvm.mlir.constant(dense<1.000000e+00> : vector<1x192xf8E4M3FN>) : !llvm.array<1 x vector<192xf8E4M3FN>>
    llvm.return %0 : !llvm.array<1 x vector<192xf8E4M3FN>>
  }
}

However, it should be

module {
  llvm.func @canonicalize_extract_shapecast_different_element_type() -> !llvm.array<1 x vector<192xi8>> {
    %0 = llvm.mlir.constant(dense<1.000000e+00> : vector<1x192xf8E4M3FN>) : !llvm.array<1 x vector<192xi8>>
    llvm.return %0 : !llvm.array<1 x vector<192xi8>>
  }
}

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@newling newling Jul 22, 2025

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Hi @MengmSun -- I just tried your example above on this branch with mlir-opt -convert-to-llvm --canonicalize test.mlir and it gives

llvm.func @canonicalize_extract_shapecast_different_element_type() -> !llvm.array<1 x vector<192xi8>> {
  %0 = llvm.mlir.constant(dense<1.000000e+00> : vector<1x192xf8E4M3FN>) : !llvm.array<1 x vector<192xi8>>
  llvm.return %0 : !llvm.array<1 x vector<192xi8>>
}

which I think is what we want

if (curType == newType)
return *this;

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