• Jack Applegame (40/40) Aug 18 2017 I explore the possibility of using D for bare metal ARM
• kinke (9/12) Aug 18 2017 Afaik, this has been brought up multiple times already and is so
• kinke (7/19) Aug 18 2017 Sorry, I forgot some workaround code:
• Jack Applegame (32/54) Aug 19 2017 Thanks for the answer. Also I found another workaround code:
• Johan Engelen (9/15) Aug 22 2017 https://issues.dlang.org/show_bug.cgi?id=11331
• Johan Engelen (2/4) Aug 22 2017 2017.

Jack Applegame <japplegame gmail.com> writes:

I explore the possibility of using D for bare metal ARM 
programming.

For some reason, the LDC default initializes the structure, even 
if initialization of all its members is specified as void. I 
believe that this is wrong.

test.d
****************************************
module test;

import core.bitop : volatileStore;

struct Foo {
	uint[64] m = void; // no default initialization
	this(uint a) {
		foreach(ref b; m) volatileStore(&b,a++);
	}
}

void ResetHandler() {
	auto foo = Foo(10);
}
****************************************

$ldc2 -mtriple=thumb-none-linux-eabi -mcpu=cortex-m3 -c --betterC 
--boundscheck=off -relocation-model=static -O3 -vcolumns test.d

test.o assembly
****************************************
00000000 <_D4test12ResetHandlerFZv>:
    0:   b510            push    {r4, lr}

    4:   466c            mov     r4, sp                   | 
default initialization

    a:   4620            mov     r0, r4                   | WHY???
    c:   f7ff fffe       bl      0 <__aeabi_memclr4>     -+





   1e:   d1f8            bne.n   12 <_D4test12ResetHandlerFZv+0x12>

   22:   bd10            pop     {r4, pc}
*****************************************

kinke <kinke gmx.net> writes:

On Friday, 18 August 2017 at 09:42:25 UTC, Jack Applegame wrote:
 For some reason, the LDC default initializes the structure, 
 even if initialization of all its members is specified as void. 
 I believe that this is wrong.

Afaik, this has been brought up multiple times already and is so 
by design. Every aggregate has an init symbol, omitting that (and 
accordingly the default initialization of all instances) by 
initializing each field with void doesn't work. The 
initialization isn't performed fieldwise, but is a bitcopy of 
T.init.
You can skip initialization of specific instances though - `S s = 
void;` - but again not if `s` is a field of another aggregate.

kinke <noone nowhere.com> writes:

On Friday, 18 August 2017 at 12:09:04 UTC, kinke wrote:
 On Friday, 18 August 2017 at 09:42:25 UTC, Jack Applegame wrote:
 For some reason, the LDC default initializes the structure, 
 even if initialization of all its members is specified as 
 void. I believe that this is wrong.

 Afaik, this has been brought up multiple times already and is 
 so by design. Every aggregate has an init symbol, omitting that 
 (and accordingly the default initialization of all instances) 
 by initializing each field with void doesn't work. The 
 initialization isn't performed fieldwise, but is a bitcopy of 
 T.init.
 You can skip initialization of specific instances though - `S s 
 = void;` - but again not if `s` is a field of another aggregate.

Sorry, I forgot some workaround code:

void ResetHandler() {
     Foo foo = void;
     foo.__ctor(10);
     // or: std.conv.emplace(&foo, 10);
}

Jack Applegame <japplegame gmail.com> writes:

On Friday, 18 August 2017 at 17:28:38 UTC, kinke wrote:
 On Friday, 18 August 2017 at 12:09:04 UTC, kinke wrote:
 On Friday, 18 August 2017 at 09:42:25 UTC, Jack Applegame 
 wrote:
 For some reason, the LDC default initializes the structure, 
 even if initialization of all its members is specified as 
 void. I believe that this is wrong.

 Afaik, this has been brought up multiple times already and is 
 so by design. Every aggregate has an init symbol, omitting 
 that (and accordingly the default initialization of all 
 instances) by initializing each field with void doesn't work. 
 The initialization isn't performed fieldwise, but is a bitcopy 
 of T.init.
 You can skip initialization of specific instances though - `S 
 s = void;` - but again not if `s` is a field of another 
 aggregate.

 Sorry, I forgot some workaround code:

 void ResetHandler() {
     Foo foo = void;
     foo.__ctor(10);
     // or: std.conv.emplace(&foo, 10);
 }

Thanks for the answer. Also I found another workaround code:

test.d
****************************************
module test;

import core.bitop : volatileStore;

struct Foo {
	uint[64] m = void; // no default initialization
	static auto opCall(uint a) {
		Foo foo = void;
		foreach(ref b; foo.m) volatileStore(&b,a++);
		return foo;
	}
}

void ResetHandler() {
	auto foo = Foo(10);
}
****************************************

assembly
****************************************
00000000 <_D4test12ResetHandlerFZv>:


    4:   4669            mov     r1, sp




   12:   d1f8            bne.n   6 <_D4test12ResetHandlerFZv+0x6>

   16:   4770            bx      lr
****************************************

Johan Engelen <j j.nl> writes:

On Friday, 18 August 2017 at 12:09:04 UTC, kinke wrote:
 On Friday, 18 August 2017 at 09:42:25 UTC, Jack Applegame wrote:
 For some reason, the LDC default initializes the structure, 
 even if initialization of all its members is specified as 
 void. I believe that this is wrong.

 Afaik, this has been brought up multiple times already and is 
 so by design.

https://issues.dlang.org/show_bug.cgi?id=11331
https://issues.dlang.org/show_bug.cgi?id=11817
https://issues.dlang.org/show_bug.cgi?id=15951

It was discussed briefly during my DConf 2016 talk, and the 
status is that it is considered a performance bug. But it'll 
require spec changes / clarifications; Johannes listed a number 
already and maybe more it needed.

- Johan

Johan Engelen <j j.nl> writes:

On Tuesday, 22 August 2017 at 18:26:46 UTC, Johan Engelen wrote:
 
 It was discussed briefly during my DConf 2016 talk

2017.