Re: [Valgrind-users] Valgrind and half-precision floating point

[Vasily G. <vas...@gm...>]

Mr. Goldsmith,

Yes, now Valgrind doesn't know VCVBT and VCVTT instructiosn on ARM.
So, please, create bug in bug-tracker. For reproducing it is better to
use "__asm__ __volatile__ (...)".
I'll try to go deeper in VEX library and if it is successfully -
produce patch and attach it to the bug. In any case, for me it is not
an issue for 1-2 hours, unfortunately.

Vasily

On Tue, Jan 7, 2014 at 2:19 AM, David Goldsmith <da...@ve...> wrote:
> Trying to reduce memory usage in my application running on an ARM Cortex-A5
> (Vybrid VF6 specifically) I converted a large array of floats to __fp16, and
> compiled with -mfp16-format=ieee.  Seems to work flawlessly (the lost
> precision is undetectable to my ear), but when I run it through valgrind it
> fails:
>     disInstr(arm): unhandled instruction: 0xEEF27A67
>                  cond=14(0xE) 27:20=239(0xEF) 4:4=0 3:0=7(0x7)
> Assembly output of the instruction in question is "vcvtb.f32.f16 s15, s15",
> convert from half-precision floating point to single-precision.
> Does Valgrind simply not support half-precision floating-point conversion?
> Should I raise this as a bug or accept my fate?  Or am I doing something
> wrong?
> Here's the basic example I compile and run through valgrind-3.9.0 (specific
> tool doesn't make a difference)
>     #include <stdio.h>
>     int main()
>     {
>         __fp16 foo = 1.1f;
>         float bar;
>         bar = (float)foo; /* Failed instruction vcvtb.f32.f16 here */
>         bar *= 2.1f;
>         printf("foo = %f, bar = %f\n", foo, bar);
>     }
>
> Since I have literally found absolutely nothing about valgrind's support of
> half-precision floating point I'm left to assume it is entirely non-existent
> with no current interest in changing that, is that correct?
>
> Thanks for any advice.
>
>
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-- 
Best Regards,
Vasily