Messages in this thread | | | Subject | Re: [PATCH] asm-generic: fix -Wtype-limits compiler warnings | From | Qian Cai <> | Date | Wed, 24 Jul 2019 14:45:52 -0400 |
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On Wed, 2019-07-24 at 08:49 +0100, David Howells wrote: > Qian Cai <cai@lca.pw> wrote: > > > Fix it by moving almost all of this multi-line macro into a proper > > function __get_order(), and leave get_order() as a single-line macro in > > order to avoid compilation errors. > > The idea was that you could compile-time initialise a global variable with > get_order(): > > int a = get_order(SOME_MACRO); > > This is the same reason that ilog2() is a macro: > > int a = ilog2(SOME_MACRO); > > See the banner comment on get_order(): > > * This function may be used to initialise variables with compile time > * evaluations of constants. > > If you're moving the constant branch into __get_order(), an inline function, > then we'll no longer be able to do this and you need to modify the comment > too. In fact, would there still be a point in having the get_order() macro? > > Also, IIRC, older versions of gcc see __builtin_constant_p(n) == 0 inside an > function, inline or otherwise, even if the passed-in argument *is* constant.
I have GCC 8.2.1 which works fine.
# cat const.c #include <stdio.h>
static int i = 0;
static inline void check() { if (__builtin_constant_p(i)) printf("i is a const.\n"); }
void main() { check(); }
# gcc -O2 const.c -o const
# ./const i is a const.
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