Intel ADX (Multi-Precision Add-Carry Instruction Extensions) is Intel's arbitrary-precision arithmetic extension to the x86 instruction set architecture (ISA).
Intel ADX was first supported in the Broadwell microarchitecture.
[1][2] The instruction set extension contains just two new instructions, though MULX from BMI2 is also considered as a part of the large integer arithmetic support.
Having two versions affecting different flags means that two chains of additions with carry can be calculated in parallel.
[3] AMD added support in their processors for these instructions starting with Ryzen.