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Re: [COMMITTED] tilegx: enable wordsize-64 support for ieee745 dbl-64.
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Chris Metcalf <cmetcalf at ezchip dot com>
- Cc: Joseph Myers <joseph at codesourcery dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 23 Dec 2014 13:21:03 -0800
- Subject: Re: [COMMITTED] tilegx: enable wordsize-64 support for ieee745 dbl-64.
- Authentication-results: sourceware.org; auth=none
- References: <201412231905 dot sBNJ5c3C004622 at farm-0002 dot internal dot tilera dot com> <alpine dot DEB dot 2 dot 10 dot 1412231958370 dot 31777 at digraph dot polyomino dot org dot uk> <5499D4FE dot 8070405 at ezchip dot com> <5499DA84 dot 3010205 at ezchip dot com>
On Tue, Dec 23, 2014 at 1:11 PM, Chris Metcalf <email@example.com> wrote:
> On 12/23/2014 3:47 PM, Chris Metcalf wrote:
>> On 12/23/2014 3:06 PM, Joseph Myers wrote:
>>> I take it that the ABI on tilegx32 allows the lround alias to llround
>> No, it doesn't - I missed this possibility. I assume the best fix is to
>> provide an lround override in sysdeps/tile/tilegx/tilegx32/s_lround.c
>> that invokes llround() and then sign-extends the result?
>> But, why doesn't MIPS itself use this approach?
>> Thanks for catching this!
> Actually, it is, of course, a little trickier than that, since
> we have to prevent s_llround.c from setting up the alias for
> lround() as well. But I think it may make sense to use global
> conditional logic to do this. The current users of dbl-64/wordsize-64
> are aarch64, alpha, sparc64, and x86_64. So as far as I know, the
> question is whether the forthcoming ILP32 version of aarch64 would
> benefit from this hack (probably yes) and whether the existing x32
> version of x86_64 would (not clear to me, but plausibly better to clean
> up the high bits of the returned value). If it's OK to just add
> ILP32-conditional logic, we can do use the appended diff.
> If not, the simplest thing for me to do would be to just add s_lround.c
> and s_llround.c in sysdeps/tile/tilegx/tilegx32 that use the default
> versions of dbl-64 and not worry about the slight performance
> improvement from using the full 64-bit register size. Or, we could
> come up with some way to use a conditional in this code: for example,
> just add a random #ifdef, #define it in a tilegx-specific override
> of s_llround.c, and #include the standard version explicitly. But
> this runs counter to the glibc rule of avoiding #ifdef. I'm not sure what
> the cleanest path would be if the use of "#ifdef _LP64" isn't OK.
> --- a/sysdeps/ieee754/dbl-64/wordsize-64/s_llround.c
> +++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_llround.c
> @@ -64,16 +64,31 @@ __llround (double x)
> weak_alias (__llround, llround)
> #ifdef NO_LONG_DOUBLE
> -strong_alias (__llround, __lroundl)
> -weak_alias (__llround, lroundl)
> +strong_alias (__llround, __llroundl)
> +weak_alias (__llround, llroundl)
> -/* long has the same width as long long on 64-bit machines. */
> +/* long has the same width as long long on 64-bit machines.
> + If building for ILP32 on a machine with 64-bit registers, however,
> + do an explicit cast on the return value instead. */
> #undef lround
> #undef __lround
> +#ifdef _LP64
> strong_alias (__llround, __lround)
> weak_alias (__llround, lround)
> -#ifdef NO_LONG_DOUBLE
> -strong_alias (__llround, __llroundl)
> -weak_alias (__llround, llroundl)
> +# ifdef NO_LONG_DOUBLE
> +strong_alias (__llround, __lroundl)
> +weak_alias (__llround, lroundl)
> +# endif
> +long int
> +__lround (double x)
> + return __llround (x);
> +weak_alias (__lround, lround)
> +# ifdef NO_LONG_DOUBLE
> +strong_alias (__lround, __lroundl)
> +weak_alias (__lround, lroundl)
> +# endif
Please make sure that x32 version is unchanged where
lround is an alias of llround.