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[mlir][vector][nfc] Add clarification on "dim-1" bcast #125425

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Feb 11, 2025
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[mlir][vector][nfc] Add clarification on "dim-1" bcast #125425

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7 changes: 4 additions & 3 deletions mlir/include/mlir/Dialect/Vector/IR/VectorOps.td
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Original file line number Diff line number Diff line change
Expand Up @@ -373,8 +373,9 @@ def Vector_BroadcastOp :

The source operand is duplicated over all the missing leading dimensions
and stretched over the trailing dimensions where the source has a non-equal
dimension of 1. These rules imply that any scalar broadcast (k=0) to any
shaped vector with the same element type is always legal.
dimension of 1 (stretching a trailing dimension is also referred to as
"dim-1" broadcasting). These rules imply that any scalar broadcast (k=0) to
any shaped vector with the same element type is always legal.

Example:

Expand All @@ -396,7 +397,7 @@ def Vector_BroadcastOp :

/// Broadcast `value` to a vector of `dstShape`, knowing that exactly the
/// `broadcastedDims` dimensions in the dstShape are broadcasted.
/// This requires (and asserts) that the broadcast is free of dim-1
/// This requires (and asserts) that the broadcast is free of "dim-1"
/// broadcasting.
/// Since vector.broadcast only allows expanding leading dimensions, an extra
/// vector.transpose may be inserted to make the broadcast possible.
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8 changes: 4 additions & 4 deletions mlir/lib/Dialect/Vector/IR/VectorOps.cpp
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Expand Up @@ -2355,7 +2355,7 @@ computeBroadcastedUnitDims(ArrayRef<int64_t> srcShape,
for (auto [s1, s2] :
llvm::zip_equal(srcShape, dstShape.drop_front(rankDiff))) {
if (s1 != s2) {
assert(s1 == 1 && "expected dim-1 broadcasting");
assert(s1 == 1 && "expected \"dim-1\" broadcasting");
res.insert(dstDim);
}
++dstDim;
Expand All @@ -2374,7 +2374,7 @@ llvm::SetVector<int64_t> BroadcastOp::computeBroadcastedUnitDims() {

/// Broadcast `value` to a vector of `dstShape`, knowing that exactly the
/// `broadcastedDims` dimensions in the dstShape are broadcasted.
/// This requires (and asserts) that the broadcast is free of dim-1
/// This requires (and asserts) that the broadcast is free of "dim-1"
/// broadcasting.
/// Since vector.broadcast only allows expanding leading dimensions, an extra
/// vector.transpose may be inserted to make the broadcast possible.
Expand Down Expand Up @@ -2460,10 +2460,10 @@ Value BroadcastOp::createOrFoldBroadcastOp(
// 3.c. Append the srcShape.
llvm::append_range(broadcastShape, srcVectorType.getShape());

// Ensure there are no dim-1 broadcasts.
// Ensure there are no "dim-1" broadcasts.
assert(::computeBroadcastedUnitDims(srcVectorType.getShape(), broadcastShape)
.empty() &&
"unexpected dim-1 broadcast");
"unexpected \"dim-1\" broadcast");

VectorType broadcastType = VectorType::get(broadcastShape, elementType);
assert(vector::isBroadcastableTo(value.getType(), broadcastType) ==
Expand Down