Is GEMM used in Tensorflow, Theano, Pytorch
Those Frameworks are based on Cuda, which is the parallel computing tool for GPUs. Specificaly it is cuDNN that is used by the deep learning framework.

You can find the user guide : https://docs.nvidia.com/deeplearning/sdk/pdf/cuDNN-Developer-Guide.pdf

All off the operations are described and indeed GEMM algorithms are used for convolution operations.