https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81156
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- Different OSes (and sometimes different compilers) have different tgmath.h implementations. Those implementations typically expand calls to tgmath.h macros to expansions that repeat their arguments many times. You have sqrt(pow(sqrt(pow()))). In glibc's tgmath.h, pow expands to repeat each of its arguments 58 times, and sqrt repeats each of its arguments 57 times. So you have 58*57*58*57 = 10929636 repetitions of each of the arguments to each of the inner pow calls, even before accounting for all of the other text in there, and all those tokens need to be generated and parsed even though most of it ends up getting folded away eventually. I expect in principle your code could compile given enough memory and time, but "enough" might be very large. Maybe I should implement __builtin_tgmath to allow macros that expand each argument once only, which is clearly best for such macros to allow deeply nested calls. (My inclination is to prefer a smart __builtin_tgmath that can be used for all tgmath.h macros, instead of several dumber variants such as I previously suggested in projects/c-frontend.html; it would be desirable for it to be able to handle TS 18661-1 functions that round result to narrower type and TS 18661-3 types as well. Such builtins would probably be necessary for implementing TS 18661-5 __STDC_TGMATH_OPERATOR_EVALUATION__.)
