On Fri, 14 Oct 2016 20:55:30 +0200 Dimitry Andric <dimi...@andric.com> wrote:
> On 14 Oct 2016, at 04:06, Ed Maste <ema...@freebsd.org> wrote:
>> On 14 October 2016 at 01:53, Bruce Evans <b...@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.
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