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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: avoiding builtin memset
Date: Wed, 26 Apr 2017 08:35:05 +0100
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Date: 2017-04-26T08:35:05+01:00
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Luke A. Guest <laguest@archeia.com> writes:

> Shark8 <onewingedshark@gmail.com> wrote:
>  
>>> You'll need to export that as the C memset function.
>> 
>> Even if you're only using it in Ada functions?
>
>
> Yup, GNAT expects certain functions to be present and generates calls
> to them. Check system.ads for mention of allowing assignment, that
> basically calls memcpy on assignment for objects that require a memory
> copy rather than a register to register copy.

Not quite sure this is set in system.ads: in the 6.1 sources, the only
reference to memset in the compiler itself is in exp_aggr.adb,

   --  The ultimate goal is to generate a call to a fast memset routine
   --  specifically optimized for the target.

   function Aggr_Assignment_OK_For_Backend (N : Node_Id) return Boolean is

whereas for System.Support_Composite_Assign there is in sem_ch5.adb

   --  Check for non-allowed composite assignment

   if not Support_Composite_Assign_On_Target
     and then (Is_Array_Type (T1) or else Is_Record_Type (T1))
     and then (not Has_Size_Clause (T1) or else Esize (T1) > 64)
   then
      Error_Msg_CRT ("composite assignment", N);
   end if;

(don't like the look of that 'Esize (T1) > 64'!)