From: Jonathan Nieder <jrnieder@gmail.com>
Date: Wed, 16 Mar 2011 09:31:08 GMT
Subject: Re: [PATCH 2/8] compat: make gcc bswap an inline function
Message-ID: <20110316093108.GB7886@elie>
In-Reply-To: <4D808126.8070706@viscovery.net>

Johannes Sixt wrote:
> Am 3/16/2011 8:00, schrieb Jonathan Nieder:

>> +static inline uint32_t git_bswap32(uint32_t x)
>> +{
>> +	uint32_t result;
>> +	if (__builtin_constant_p(x))
>
> Can this predicate ever be true? Isn't it false even if the function is
> inlined?

It's true if x is a constant.

$ cat test.c
#if 0
gcc -Wall -W -O -o tryit "$0"
exec ./tryit
#else
#include <stdio.h>
#include <stdint.h>

#ifdef __GNUC__
static inline int constant(uint32_t x)
{
	return __builtin_constant_p(x);
}
#else
static inline int constant(uint32_t x) { return 0; }
#endif

int main(void)
{
	printf("%d\n", constant(3 + 5));
	return 0;
}
#endif
$ ./test.c
1