What is this Lisp dialect, used in GCC internals?

What programming language is this? It's a Lisp dialect used by GCC internals.

(define_insn "*call_symbol"
   [(call (mem:DI (match_operand:DI 0 "" ""))
          (match_operand 1 "" ""))
    (use (match_operand 2 "" ""))
    (clobber (reg:DI LR_REGNUM))]
   "GET_CODE (operands[0]) == SYMBOL_REF
    && !aarch64_is_long_call_p (operands[0])"
   "bl\\t%a0"
   [(set_attr "type" "call")]
)

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