================
@@ -298,16 +298,139 @@ struct LegalizeSVEMaskLoadConversion : public
OpRewritePattern<memref::LoadOp> {
}
};
+/// Transforms a `transfer_read` operation so it reads vector of a type that
+/// can be mapped to an LLVM type. This is done by collapsing trailing
+/// dimensions so we obtain a vector type with a single scalable dimension in
+/// the rightmost position.
+///
+/// Example:
+/// ```
+/// %v = vector.transfer_read %M[%i, %j, %c0, %c0], %c0_i8
+/// {in_bounds = [false, true, true, true]}
+/// : memref<?x?x2x8xi8>, vector<2x[4]x2x8xi8>
+/// ```
+/// is rewritten to
+/// ```
+/// %collapse_shape = memref.collapse_shape %M [[0], [1, 2, 3]]
+/// : memref<?x?x2x8xi8> into memref<?x?xi8>
+/// %0 = vector.transfer_read %collapse_shape[%i, %j], %c0_i8
+/// {in_bounds = [false, true]}
+/// : memref<?x?xi8>, vector<2x[64]xi8>
+/// %1 = vector.shape_cast %0 : vector<2x[64]xi8> to vector<2x[4]x2x8xi8>
+/// ```
+struct LegalizeTransferRead : public OpRewritePattern<vector::TransferReadOp> {
+ using OpRewritePattern::OpRewritePattern;
+
+ LogicalResult matchAndRewrite(vector::TransferReadOp readOp,
+ PatternRewriter &rewriter) const override {
+
+ // Do not try to transform masked reads. For example, if we have a transfer
+ // to a `vector<[4]x4xi8>` we could have a mask like
+ // 1 1 1 0
+ // 1 1 1 0
+ // 1 1 1 0
+ // 0 0 0 0
+ // Flattening this mask would look like
+ // 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0
+ // and we have not yet figured out an efficient way to build such a mask,
+ // neither from the mask operand, nor from the original
`vector.create_mask`
+ // operation (if visible at all).
+ if (readOp.isMasked() || readOp.getMask())
+ return rewriter.notifyMatchFailure(readOp,
+ "masked transfers not-supported");
+
+ if (!readOp.getPermutationMap().isMinorIdentity())
+ return rewriter.notifyMatchFailure(readOp, "non-identity permutation");
----------------
banach-space wrote:
Would supporting non-identity be a problem? It would be good to add a comment,
either:
* `TODO: We haven't required this, so leaving for later.` or
* "Too complex because of <some reason>, disabling".
Any hint for future developers would be helpful.
https://github.com/llvm/llvm-project/pull/143146
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