Re: Some functions are not inlined by gcc 3.2, resulting code is ugly

Denis Vlasenko (vda@port.imtp.ilyichevsk.odessa.ua)
Mon, 4 Nov 2002 14:08:10 -0200


On 3 November 2002 18:28, Alan Cox wrote:
> On Mon, 2002-11-04 at 00:20, Denis Vlasenko wrote:
> > __constant_c_and_count_memset *has to* be inlined.
> > There is large switch statement which meant to be optimized out.
> > It does optimize out *only if* count is compile-time constant.
>
> gcc already allows you to check for constants that means you can
> generate
>
> (is a constant ? inline: noninline)(to, from, len)
^^^^^^
>
> and I would hope gcc does the right thing. Similarly your switch will
> be optimised out so the default case for the constant one can be the
> invocation of uninlined code and it should optimise back to the
> straight expected call.

Yes. That is how it is done right now in 2.4 and 2.5. The problem is
that gcc 3.2 did *not* inline __constant_c_and_count_memset()
as we all expected.

What's the verdict on my patch?

--
vda

diff -urN linux-2.5.45.orig/include/asm-i386/string.h linux-2.5.45fix/include/asm-i386/string.h --- linux-2.5.45.orig/include/asm-i386/string.h Wed Oct 30 22:43:46 2002 +++ linux-2.5.45fix/include/asm-i386/string.h Sun Nov 3 15:58:08 2002 @@ -3,6 +3,7 @@

#ifdef __KERNEL__ #include <linux/config.h> +#include <linux/compiler.h> /* * On a 486 or Pentium, we are better off not using the * byte string operations. But on a 386 or a PPro the @@ -218,7 +219,7 @@ * This looks horribly ugly, but the compiler can optimize it totally, * as the count is constant. */ -static inline void * __constant_memcpy(void * to, const void * from, size_t n) +static force_inline void * __constant_memcpy(void * to, const void * from, size_t n) { switch (n) { case 0: @@ -453,7 +454,7 @@ * This looks horribly ugly, but the compiler can optimize it totally, * as we by now know that both pattern and count is constant.. */ -static inline void * __constant_c_and_count_memset(void * s, unsigned long pattern, size_t count) +static force_inline void * __constant_c_and_count_memset(void * s, unsigned long pattern, size_t count) { switch (count) { case 0: diff -urN linux-2.5.45.orig/include/linux/compiler.h linux-2.5.45fix/include/linux/compiler.h --- linux-2.5.45.orig/include/linux/compiler.h Wed Oct 30 22:43:05 2002 +++ linux-2.5.45fix/include/linux/compiler.h Sun Nov 3 15:19:20 2002 @@ -20,3 +20,11 @@ __asm__ ("" : "=g"(__ptr) : "0"(ptr)); \ (typeof(ptr)) (__ptr + (off)); }) #endif /* __LINUX_COMPILER_H */ + +/* GCC 3 (and probably earlier, I'm not sure) can be told to always inline + a function. */ +#if __GNUC__ < 3 +#define force_inline inline +#else +#define force_inline inline __attribute__ ((always_inline)) +#endif - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/