llvm dev - Jul 2018 - sizeof(DIFlags)

Hi list,

Is there a standards based reason why the DIFlags enum is set to
uint32_t[1]? I am sure my DWARF-std-reading-fu is not up to snuff and so
I cannot seem to find it.
The reason I ask is that we are running out of space for our own DIFlags
and would like to nail this down before deciding on an approach.
Thanks!

Sohail 

[1] The code in question:
   
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/DebugInfoMetadata.h#L194

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180716/2f01fd98/attachment.html>

DIFlags is internal to the compiler, not directly determined by the DWARF
standard.  It mostly happens to be full of data that gets turned into DWARF
flags.
I suspect it's nailed down to 32 bits mainly because we haven't needed
more, so far.  Also MSVC historically failed to handle enum values wider than 32
bits; I don't know whether that's still true.
--paulr

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Sohail
Somani (Fizz Buzz Inc.) via llvm-dev
Sent: Monday, July 16, 2018 8:57 AM
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] sizeof(DIFlags)

Hi list,

Is there a standards based reason why the DIFlags enum is set to uint32_t[1]? I
am sure my DWARF-std-reading-fu is not up to snuff and so I cannot seem to find
it.

The reason I ask is that we are running out of space for our own DIFlags and
would like to nail this down before deciding on an approach.

Thanks!

Sohail

[1] The code in question:
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/DebugInfoMetadata.h#L194


-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180716/a4b4e2cf/attachment.html>

Thanks Paul! This was our conclusion as well so it's encouraging that
you feel similarly. The next question is whether these are being cast to
int/unsigned somewhere. That will be fun to track down :)
On Mon, Jul 16, 2018, at 1:17 PM, paul.robinson at sony.com
wrote:
> DIFlags is internal to the compiler, not directly determined by the
> DWARF standard.  It mostly happens to be full of data that gets turned
> into DWARF flags.> I suspect it's nailed down to 32 bits mainly
because we haven't needed
> more, so far.  Also MSVC historically failed to handle enum values
> wider than 32 bits; I don't know whether that's still true.>
--paulr
>  
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf
> Of *Sohail Somani (Fizz Buzz Inc.) via llvm-dev *Sent:* Monday, July
> 16, 2018 8:57 AM *To:* llvm-dev at lists.llvm.org *Subject:* [llvm-dev]
> sizeof(DIFlags)>  
> Hi list,
>  
> Is there a standards based reason why the DIFlags enum is set to
> uint32_t[1]? I am sure my DWARF-std-reading-fu is not up to snuff and
> so I cannot seem to find it.>  
> The reason I ask is that we are running out of space for our own
> DIFlags and would like to nail this down before deciding on an
> approach.>  
> Thanks!
>  
> Sohail 
>  
> [1] The code in question:
>    
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/DebugInfoMetadata.h#L194>
>  


-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180716/7c2c8f29/attachment-0001.html>

I think mainly to ensure that we don't have extra padding in DIType objects:

class DIType : public DIScope {
  unsigned Line;
  DIFlags Flags;
  uint64_t SizeInBits;
  uint64_t OffsetInBits;
  uint32_t AlignInBits;

If DIFlags grew to 64-bits, we'd want to re-arrange things to save memory.
DITypes have been known to consume large amounts of memory.

On Mon, Jul 16, 2018 at 5:57 AM Sohail Somani (Fizz Buzz Inc.) via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi list,
>
> Is there a standards based reason why the DIFlags enum is set to
> uint32_t[1]? I am sure my DWARF-std-reading-fu is not up to snuff and so I
> cannot seem to find it.
>
> The reason I ask is that we are running out of space for our own DIFlags
> and would like to nail this down before deciding on an approach.
>
> Thanks!
>
> Sohail
>
> [1] The code in question:
>
https://github.com/llvm-mirror/llvm/blob/master/include/llvm/IR/DebugInfoMetadata.h#L194
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20180716/3a17b136/attachment.html>