[mlir][sparse] first end-to-end matmul with codegen

(1) also fixes memory leak in sparse2dense rewriting
(2) still needs fix in dense2sparse by skipping zeros

Reviewed By: wrengr

Differential Revision: https://reviews.llvm.org/D137736

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorRewriting.cpp

@@ -564,7 +564,10 @@ private:
 
     SmallVector<Value, 4> sizes;
     sizesForTensor(rewriter, sizes, loc, srcTp, src);
+
     Value dst = allocDenseTensor(rewriter, loc, dstTp, sizes);
+    Block *insertionBlock = rewriter.getInsertionBlock();
+    bool noEscape = bufferization::allocationDoesNotEscape(op->getOpResult(0));
 
     rewriter.create<ForeachOp>(loc, src, llvm::None,
                                [&](OpBuilder &builder, Location loc,
@@ -575,6 +578,12 @@ private:
                                });
 
     rewriter.replaceOpWithNewOp<bufferization::ToTensorOp>(op, dstTp, dst);
+
+    // Deallocate the buffer.
+    if (noEscape) {
+      rewriter.setInsertionPoint(insertionBlock->getTerminator());
+      deallocDenseTensor(rewriter, loc, dst);
+    }
     return success();
   }