http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904
--- Comment #32 from Dominique d'Humieres <dominiq at lps dot ens.fr> 2011-12-02 16:37:37 UTC --- > And for the sake of completeness the evaluation of sub above and > > subroutine sub2(x) > real*8 x > x = (x + 2.d0**52) - 2.d0**52 > end subroutine sub2 > > should behave consistently if I read your Fortran standard > quotations correctly. According my reading of > "Once the interpretation of a numeric intrinsic operation is established, the > processor may evaluate any mathematically equivalent expression, provided that > the integrity of parentheses is not violated." this is different from > subroutine sub(x) > real*8 x, tem > tem = x + 2.d0**52 > x = tem - 2.d0**52 > end subroutine sub where 'x=tem-2.d0**52' can be evaluated as 'x=x+2.d0**52-2.d0**52' then as 'x' (as long as x and tmp are of the same kind(?)), while in the former case '(x + 2.d0**52) - 2.d0**52' is prohibited by the standard to be evaluated as 'x'. Note that if I replace 'tem = x + 2.d0**52' with 'tem = (x + 2.d0**52)', I get 1.0 unless I use -fno-protect-parens. All this has been discussed previously, but the only pr I have been to find is pr32172.
