svn commit: r307231 - head/lib/libgcc_s

[Tijl Coosemans]

On Fri, 14 Oct 2016 20:55:30 +0200 Dimitry Andric <dimitry at andric.com> wrote:
> On 14 Oct 2016, at 04:06, Ed Maste <emaste at freebsd.org> wrote:
>> On 14 October 2016 at 01:53, Bruce Evans <brde at optusnet.com.au> wrote:  
>>>> compiler-rt's complex division support routines contain calls to
>>>> compiler builtins such as `__builtin_scalbnl`.  Unfortunately Clang
>>>> turns these back into a call to `scalbnl`.  
>>> 
>>> gcc-4.2 has the same bug.  
>> 
>> Oh, interesting. Do you know off hand if it's resolved in later GCC?  
> 
> Not for x86, in any case (I think I talked about this with you on IRC
> before).  For example, using the latest gcc 7.0.0 20160911 on this
> program:
> 
> float f1(float x, int n)
> {
> 	return __builtin_scalbnf(x, n);
> }
> 
> double f2(double x, int n)
> {
> 	return __builtin_scalbn(x, n);
> }
> 
> long double f3(long double x, long n)
> {
> 	return __builtin_scalbnl(x, n);
> }
> 
> gives this assembly:
> 
> 	.p2align 4,,15
> 	.globl	f1
> 	.type	f1, @function
> f1:
> .LFB0:
> 	.cfi_startproc
> 	jmp	scalbnf
> 	.cfi_endproc
> .LFE0:
> 	.size	f1, .-f1
> 	.p2align 4,,15
> 	.globl	f2
> 	.type	f2, @function
> f2:
> .LFB1:
> 	.cfi_startproc
> 	jmp	scalbn
> 	.cfi_endproc
> .LFE1:
> 	.size	f2, .-f2
> 	.p2align 4,,15
> 	.globl	f3
> 	.type	f3, @function
> f3:
> .LFB2:
> 	.cfi_startproc
> 	jmp	scalbnl
> 	.cfi_endproc
> .LFE2:
> 	.size	f3, .-f3
> 
> E.g., it looks like the __builtin_scalbn functions were always a red
> herring. :-)

From https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html:

GCC includes built-in versions of many of the functions in the standard C
library. These functions come in two forms: one whose names start with
the __builtin_ prefix, and the other without. Both forms have the same
type (including prototype), the same address (when their address is
taken), and the same meaning as the C library functions even if you
specify the -fno-builtin option see C Dialect Options). Many of these
functions are only optimized in certain cases; if they are not optimized
in a particular case, a call to the library function is emitted.