[mlir][VectorOps] Add conversion of 1-D vector.interleave ops to LLVM (#80966)

The 1-D case directly maps to LLVM intrinsics. The n-D case will be
handled by unrolling to 1-D first (in a later patch).

Depends on: #80965

mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp

@@ -1734,6 +1734,45 @@ struct VectorSplatNdOpLowering : public ConvertOpToLLVMPattern<SplatOp> {
   }
 };
 
+/// Conversion pattern for a `vector.interleave`.
+/// This supports fixed-sized vectors and scalable vectors.
+struct VectorInterleaveOpLowering
+    : public ConvertOpToLLVMPattern<vector::InterleaveOp> {
+  using ConvertOpToLLVMPattern::ConvertOpToLLVMPattern;
+
+  LogicalResult
+  matchAndRewrite(vector::InterleaveOp interleaveOp, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    VectorType resultType = interleaveOp.getResultVectorType();
+    // n-D interleaves should have been lowered already.
+    if (resultType.getRank() != 1)
+      return rewriter.notifyMatchFailure(interleaveOp,
+                                         "InterleaveOp not rank 1");
+    // If the result is rank 1, then this directly maps to LLVM.
+    if (resultType.isScalable()) {
+      rewriter.replaceOpWithNewOp<LLVM::experimental_vector_interleave2>(
+          interleaveOp, typeConverter->convertType(resultType),
+          adaptor.getLhs(), adaptor.getRhs());
+      return success();
+    }
+    // Lower fixed-size interleaves to a shufflevector. While the
+    // vector.interleave2 intrinsic supports fixed and scalable vectors, the
+    // langref still recommends fixed-vectors use shufflevector, see:
+    // https://llvm.org/docs/LangRef.html#id876.
+    int64_t resultVectorSize = resultType.getNumElements();
+    SmallVector<int32_t> interleaveShuffleMask;
+    interleaveShuffleMask.reserve(resultVectorSize);
+    for (int i = 0, end = resultVectorSize / 2; i < end; ++i) {
+      interleaveShuffleMask.push_back(i);
+      interleaveShuffleMask.push_back((resultVectorSize / 2) + i);
+    }
+    rewriter.replaceOpWithNewOp<LLVM::ShuffleVectorOp>(
+        interleaveOp, adaptor.getLhs(), adaptor.getRhs(),
+        interleaveShuffleMask);
+    return success();
+  }
+};
+
 } // namespace
 
 /// Populate the given list with patterns that convert from Vector to LLVM.
@@ -1758,7 +1797,8 @@ void mlir::populateVectorToLLVMConversionPatterns(
                VectorExpandLoadOpConversion, VectorCompressStoreOpConversion,
                VectorSplatOpLowering, VectorSplatNdOpLowering,
                VectorScalableInsertOpLowering, VectorScalableExtractOpLowering,
-               MaskedReductionOpConversion>(converter);
+               MaskedReductionOpConversion, VectorInterleaveOpLowering>(
+      converter);
   // Transfer ops with rank > 1 are handled by VectorToSCF.
   populateVectorTransferLoweringPatterns(patterns, /*maxTransferRank=*/1);
 }