https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121479
--- Comment #2 from Anonymous <njuwy at smail dot nju.edu.cn> --- (In reply to Jakub Jelinek from comment #1) > That is not a bug, that is exactly how __builtin_constant_p is designed and > documented: > "The function returns the integer 1 if the argument is known > to be a compile-time constant and 0 if it is not known to be a > compile-time constant. A return of 0 does not indicate that the > value is _not_ a constant, but merely that GCC cannot prove it is a > constant with the specified value of the '-O' option." Thanks (In reply to Jakub Jelinek from comment #1) > That is not a bug, that is exactly how __builtin_constant_p is designed and > documented: > "The function returns the integer 1 if the argument is known > to be a compile-time constant and 0 if it is not known to be a > compile-time constant. A return of 0 does not indicate that the > value is _not_ a constant, but merely that GCC cannot prove it is a > constant with the specified value of the '-O' option." Thanks for your reply. I will pay more attention to the use of builtin functions. BTW，I find that, at -O0, __builtin_constant_p in GCC will not return 1 even if a constant variable (like "const int x=3;") is passed in, but llvm can. https://godbolt.org/z/E946r7Pr4
