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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Tue, 9 Jan 2018 08:45:27 -0800
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Subject: Re: [Qemu-devel] [PATCH v2 02/20] include/fpu/softfloat: remove
 USE_SOFTFLOAT_STRUCT_TYPES
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To: Peter Maydell <peter.maydell@linaro.org>, Laurent Vivier <laurent@vivier.eu>
Cc: Aurelien Jarno <aurelien@aurel32.net>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, bharata@linux.vnet.ibm.com, Andrew Dutcher <andrew@andrewdutcher.com>, QEMU Developers <qemu-devel@nongnu.org>

On 01/09/2018 06:43 AM, Peter Maydell wrote:
> On 9 January 2018 at 14:20, Laurent Vivier <laurent@vivier.eu> wrote:
>> Le 09/01/2018 à 15:14, Peter Maydell a écrit :
>>> Is gcc's codegen still bad enough that we have to default to not
>>> using the type-checking versions? If so, maybe we could at least
>>> enable the type-checking on an --enable-debug build, so it doesn't
>>> bitrot all the time.
>>
>> What means "bad enough"? for some targets it works fine.
> 
> I mean whatever the problem was that made us write the comment
>    A sufficiently clever compiler and
>    sane ABI should be able to see though these structs.  However
>    x86/gcc 3.x seems to struggle a bit, so leave them disabled by default.

E.g. the i386 ABI is *not* sane in this respect.  Nor is sparcv8plus.  I'd have
to check on the others.

If we enable USE_SOFTFLOAT_STRUCT_TYPES, then we *must* remove the markup for
f32 and f64 from include/exec/helper-head.h, because structures are passed
differently from integers as parameters and/or return values.

I personally do not think USE_SOFTFLOAT_STRUCT_TYPES is worth the headache.


r~