They were used in the late 90s, and companies such as Cray had C to FPGA compilers. These were implemented as c style calls that the compiler transformed to FPG

They were used in the late 90s, and companies such as Cray had C to FPGA compilers. These were implemented as c style calls that the compiler transformed to FPGA. The coding was hard and performed below expectation. The only customers that benefited were military/intelligence agencies who were using outdated techniques such as filtering in the Fourier basis. The problem was data-transfer compounded by inflexible code generation. The data still needed to travel from RAM which meant that even without computation you couldn't get over a 50% increase in performance. It would need to be send back for more complex processing.