https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62117
--- Comment #3 from yuta tomino <demoonlit at panathenaia dot halfmoon.jp> --- I understood by trial and error that pragma Pure_Function is equivalent to __attribute__((const)). I'm sorry. The first case (in my first description) is not compiler's bug but my mistake. The parameters Left and Right were erased by optimization because compiler assumed that Pure_Function does not dereference, in my current understanding. Also, the case2 (in comment 2) is not reproduced by gcc-5. However, the reason is that System.Fat_Flt.Unaligned_Valid is removed on gcc-5. ...By the way, I found an another point that I'm concerned. In the document of pragma Pure_Function, a function having Address parameter is not considered as Pure_Function. https://gcc.gnu.org/onlinedocs/gnat_rm/Pragma-Pure_005fFunction.html > One exception is any function that has at least one formal of type > System.Address or a type derived from it. Such functions are not considered > pure by default, But, with System; package case3_p is pragma Pure; function F (X : System.Address) return System.Address; end case3_p; package body case3_p is function F (X : System.Address) return System.Address is begin return X; end F; end case3_p; with case3_p; with System.Storage_Elements; use System.Storage_Elements; with GNAT.IO; procedure case3_m is begin GNAT.IO.Put (Integer (To_Integer (case3_p.F (System'To_Address (10))))); GNAT.IO.Put (Integer (To_Integer (case3_p.F (System'To_Address (10))))); GNAT.IO.Put (Integer (To_Integer (case3_p.F (System'To_Address (10))))); end case3_m; Compile this case3_m.adb with optimization. % gcc -S -O -gnatp case3_m.adb .text .globl __ada_case3_m __ada_case3_m: LFB1: pushq %rbx LCFI0: movl $10, %edi call _case3_p__f movq %rax, %rbx movl %eax, %edi call _gnat__io__put__2 movl %ebx, %edi call _gnat__io__put__2 movl %ebx, %edi call _gnat__io__put__2 popq %rbx LCFI1: ret _case3_p__f is called once on the machine code against that case3_p.F is called three times from case3_m. Perhaps, case3_p.F is treated as Pure_Function. Which of those is correct, the document or the behaviour of compiler?
