[mlir] Fix SplatOp lowering to the LLVM dialect

[ftynse]

Summary

The lowering has been incorrectly using the operands of the original op instead
of rewritten operands provided to matchAndRewrite call. This may lead to
spurious materializations and generally invalid IR.

mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp

struct SplatOpLowering : public ConvertOpToLLVMPattern<SplatOp> {
 
   LogicalResult
   matchAndRewrite(SplatOp splatOp, ArrayRef<Value> operands,
                   ConversionPatternRewriter &rewriter) const override {
     VectorType resultType = splatOp.getType().dyn_cast<VectorType>();
     if (!resultType || resultType.getRank() != 1)
       return failure();
 
+    SplatOp::Adaptor adaptor(operands);
+
     // First insert it into an undef vector so we can shuffle it.
     auto vectorType = typeConverter->convertType(splatOp.getType());
     Value undef = rewriter.create<LLVM::UndefOp>(splatOp.getLoc(), vectorType);
     auto zero = rewriter.create<LLVM::ConstantOp>(
         splatOp.getLoc(),
         typeConverter->convertType(rewriter.getIntegerType(32)),
         rewriter.getZeroAttr(rewriter.getIntegerType(32)));
 
     auto v = rewriter.create<LLVM::InsertElementOp>(
-        splatOp.getLoc(), vectorType, undef, splatOp.getOperand(), zero);
+        splatOp.getLoc(), vectorType, undef, adaptor.input(), zero);
 
     int64_t width = splatOp.getType().cast<VectorType>().getDimSize(0);
     SmallVector<int32_t, 4> zeroValues(width, 0);
 
     // Shuffle the value across the desired number of elements.
     ArrayAttr zeroAttrs = rewriter.getI32ArrayAttr(zeroValues);
     rewriter.replaceOpWithNewOp<LLVM::ShuffleVectorOp>(splatOp, v, undef,
                                                        zeroAttrs);