| Message ID | 20200917163106.49351-5-philmd@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | qemu/bswap: Let cpu_to_endian() functions handle constant expressions | expand |
On 9/17/20 9:31 AM, Philippe Mathieu-Daudé wrote: > cpu_to_endian() and endian_to_cpu() can be extended to handle > constant expressions. That way the programmer doesn't need to > remember the const_X() API exists. > > Suggested-by: Stefan Hajnoczi <stefanha@gmail.com> > Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> > --- > include/qemu/bswap.h | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h > index de256cea3ab..8827e4760b9 100644 > --- a/include/qemu/bswap.h > +++ b/include/qemu/bswap.h > @@ -191,12 +191,16 @@ static inline void bswap64s(uint64_t *s) > #define CPU_CONVERT(endian, size, type)\ > static inline type endian ## size ## _to_cpu(type v)\ > {\ > - return glue(endian, _bswap)(v, size);\ > + return __builtin_constant_p(v) ?\ > + const_ ## endian ## size(v) :\ > + glue(endian, _bswap)(v, size);\ > }\ > \ > static inline type cpu_to_ ## endian ## size(type v)\ > {\ > - return glue(endian, _bswap)(v, size);\ > + return __builtin_constant_p(v) ?\ > + const_ ## endian ## size(v) :\ > + glue(endian, _bswap)(v, size);\ > }\ > \ > static inline void endian ## size ## _to_cpus(type *p)\ > How does this actually affect code generation? If it does, then that's a mistake in our definition of bswap{16,32,64}(), which should have been able to fold constants just fine. Looking at all of that CONFIG_MACHINE_BSWAP_H stuff, I think we should just ditch it all in favour of __builin_bswap*. The final piece, __builtin_bswap16, came in at ac868f29d7e8 in gcc-4.8. r~
diff --git a/include/qemu/bswap.h b/include/qemu/bswap.h index de256cea3ab..8827e4760b9 100644 --- a/include/qemu/bswap.h +++ b/include/qemu/bswap.h @@ -191,12 +191,16 @@ static inline void bswap64s(uint64_t *s) #define CPU_CONVERT(endian, size, type)\ static inline type endian ## size ## _to_cpu(type v)\ {\ - return glue(endian, _bswap)(v, size);\ + return __builtin_constant_p(v) ?\ + const_ ## endian ## size(v) :\ + glue(endian, _bswap)(v, size);\ }\ \ static inline type cpu_to_ ## endian ## size(type v)\ {\ - return glue(endian, _bswap)(v, size);\ + return __builtin_constant_p(v) ?\ + const_ ## endian ## size(v) :\ + glue(endian, _bswap)(v, size);\ }\ \ static inline void endian ## size ## _to_cpus(type *p)\
cpu_to_endian() and endian_to_cpu() can be extended to handle constant expressions. That way the programmer doesn't need to remember the const_X() API exists. Suggested-by: Stefan Hajnoczi <stefanha@gmail.com> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com> --- include/qemu/bswap.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)