llvm dev - Apr 2016 - Inline SmallVectorBase::grow_pod?

Hello llvm-dev,

I'm working on some out-of-process reflection support for Swift and I'd
like to switch over some of my memory management to context-based with a
bump-pointer allocator. I hit a linker error that `grow_pod` was missing.
Eventually, some of this code will get linked into the Swift runtime and we are
trying to avoid directly linking LLVM into the runtime to keep the size down, so
I can't link in Support.

I see that this method was pulled out of line for
https://llvm.org/bugs/show_bug.cgi?id=3758 back in 2009. Is there a chance we
can consider pulling it back into a header? It's kind of a shame to have to
have to link Support just to use BumpPointerAllocator.

David

> On Apr 12, 2016, at 5:59 PM, David Farler via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello llvm-dev,
> 
> I'm working on some out-of-process reflection support for Swift and
I'd like to switch over some of my memory management to context-based with a
bump-pointer allocator. I hit a linker error that `grow_pod` was missing.
Eventually, some of this code will get linked into the Swift runtime and we are
trying to avoid directly linking LLVM into the runtime to keep the size down, so
I can't link in Support.
If code size is your motivation, any dead-stripping by the linker should remove
all the code from libLLVMSupport that you are not actually using. It's not
clear how moving every pieces you need to a header would help here. Have you
some elements that shows how much of Support can't be dead-stripped from
your binary?

Having things in a header is not nice for compile-time, we should try to move
things out-of-headers instead of adding more.

-- 
Mehdi


> 
> I see that this method was pulled out of line for
https://llvm.org/bugs/show_bug.cgi?id=3758 back in 2009. Is there a chance we
can consider pulling it back into a header? It's kind of a shame to have to
have to link Support just to use BumpPointerAllocator.
> 
> David
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

> On Apr 12, 2016, at 6:08 PM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> 
> 
>> On Apr 12, 2016, at 5:59 PM, David Farler via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>> 
>> Hello llvm-dev,
>> 
>> I'm working on some out-of-process reflection support for Swift and
I'd like to switch over some of my memory management to context-based with a
bump-pointer allocator. I hit a linker error that `grow_pod` was missing.
Eventually, some of this code will get linked into the Swift runtime and we are
trying to avoid directly linking LLVM into the runtime to keep the size down, so
I can't link in Support.
> 
> If code size is your motivation, any dead-stripping by the linker should
remove all the code from libLLVMSupport that you are not actually using.
It's not clear how moving every pieces you need to a header would help here.
Have you some elements that shows how much of Support can't be dead-stripped
from your binary?
> 
> Having things in a header is not nice for compile-time, we should try to
move things out-of-headers instead of adding more.
> 
> -- 
> Mehdi
> 
> 
> 
>> 
>> I see that this method was pulled out of line for
https://llvm.org/bugs/show_bug.cgi?id=3758 back in 2009. Is there a chance we
can consider pulling it back into a header? It's kind of a shame to have to
have to link Support just to use BumpPointerAllocator.
>> 
>> David
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
There is also the fact that we simply don't compile LLVM for all target
architectures in Swift (because we don't link it into the standard library
or runtime); we only build it for the host.

David

On Tue, Apr 12, 2016 at 5:59 PM, David Farler via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
> I see that this method was pulled out of line for
> https://llvm.org/bugs/show_bug.cgi?id=3758 back in 2009. Is there a
> chance we can consider pulling it back into a header? It's kind of a
shame
> to have to have to link Support just to use BumpPointerAllocator.
>
I don't think we want to do that. It's rarely profitable to inline
grow_pod, and it wastes object file size.
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