Date: Fri, 14 Oct 2016 20:55:30 +0200 From: Dimitry Andric <dimitry@andric.com> To: Ed Maste <emaste@freebsd.org> Cc: Bruce Evans <brde@optusnet.com.au>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r307231 - head/lib/libgcc_s Message-ID: <D2B021E3-62D3-4CC6-AE6C-02D683AD7699@andric.com> In-Reply-To: <CAPyFy2ApcwgdScnX%2BaK%2BKBR5_TVkeB-Kdc6Y1HUO98uhw4fpfA@mail.gmail.com> References: <201610131918.u9DJI0bX085695@repo.freebsd.org> <20161014113603.F1039@besplex.bde.org> <CAPyFy2ApcwgdScnX%2BaK%2BKBR5_TVkeB-Kdc6Y1HUO98uhw4fpfA@mail.gmail.com>
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On 14 Oct 2016, at 04:06, Ed Maste <emaste@freebsd.org> wrote:
>
> Hi Bruce, thank you for the detailed response.
>
> On 14 October 2016 at 01:53, Bruce Evans <brde@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. :-)
> It seems particularly unfortunate for the compiler to report (by
> whatever mechanism) that a builtin exists, and then just turn that
> builtin into a library call.
Yes, at best this is misleading.
-Dimitry
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