llvm dev - Nov 2018 - Non-relocating GC with liveness tracking

Hi Team,
I'm working on a new pure functional language and I'm trying to add GC
support for that.

Because all vars are immutable, the IR that my frontend generates are all
register based, i.e. no alloca, and no readmem, writemem unless
accessing/constructing structs.

If I use the traditional GC with gcroot intrinsic, it will need to emit
more code for liveness tracking, storing the IR values into the gcroot,
which seems convoluted.

I found using stack map / statepoints very plausible here, because it only
needs all live vars without saving it to a corresponding gcroot, and can
track liveness at every call point.

However, this seems still marked as experimental, and doesn't support
exception handling (which is a requirement for my language). And because my
language uses return barriar (
http://lists.llvm.org/pipermail/llvm-dev/2017-August/116291.html), I'm
already using a new intrinsic that returns a token type for calls so I can
have multiple return paths that retrieves the actual result, and currently
it doesn't work with gc.statepoint.

I wanna check the status of statepoint GC: Is it still actively developed?
is there any plan to fix the exception handling path? Or should I continue
to use the gcroot intrinsic? Change my new multi-return intrinsic to
support statepoint?

I'm also thinking using a non-relocating GC with stackmap because
relocating is currently optional for me: all live roots are passed to call
site as operand bundle, so codegen can emit the stack map, and my new
intrinsic for multiple return paths can also work with that.

Any advise will be welcome.

Thanks
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I remember Haskell GHC using LLVM as its backend. Haskell is pure
functional language also. A little google search shows it supports garbage
collection, too. Looking into GHC's implementation might be help.

2017-12-09 5:29 GMT+08:00 Chuan Qiu via llvm-dev <llvm-dev at
lists.llvm.org>:
> Hi Team,
> I'm working on a new pure functional language and I'm trying to add
GC
> support for that.
>
> Because all vars are immutable, the IR that my frontend generates are all
> register based, i.e. no alloca, and no readmem, writemem unless
> accessing/constructing structs.
>
> If I use the traditional GC with gcroot intrinsic, it will need to emit
> more code for liveness tracking, storing the IR values into the gcroot,
> which seems convoluted.
>
> I found using stack map / statepoints very plausible here, because it only
> needs all live vars without saving it to a corresponding gcroot, and can
> track liveness at every call point.
>
> However, this seems still marked as experimental, and doesn't support
> exception handling (which is a requirement for my language). And because my
> language uses return barriar (http://lists.llvm.org/
> pipermail/llvm-dev/2017-August/116291.html), I'm already using a new
> intrinsic that returns a token type for calls so I can have multiple return
> paths that retrieves the actual result, and currently it doesn't work
with
> gc.statepoint.
>
> I wanna check the status of statepoint GC: Is it still actively developed?
> is there any plan to fix the exception handling path? Or should I continue
> to use the gcroot intrinsic? Change my new multi-return intrinsic to
> support statepoint?
>
> I'm also thinking using a non-relocating GC with stackmap because
> relocating is currently optional for me: all live roots are passed to call
> site as operand bundle, so codegen can emit the stack map, and my new
> intrinsic for multiple return paths can also work with that.
>
> Any advise will be welcome.
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>

-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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+CC Philip Reames and Anna Thomas from Azul Systems

On Fri, Dec 8, 2017 at 1:29 PM, Chuan Qiu via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi Team,
> I'm working on a new pure functional language and I'm trying to add
GC
> support for that.
>
> Because all vars are immutable, the IR that my frontend generates are all
> register based, i.e. no alloca, and no readmem, writemem unless
> accessing/constructing structs.
>
> If I use the traditional GC with gcroot intrinsic, it will need to emit
more
> code for liveness tracking, storing the IR values into the gcroot, which
> seems convoluted.
>
> I found using stack map / statepoints very plausible here, because it only
> needs all live vars without saving it to a corresponding gcroot, and can
> track liveness at every call point.
>
> However, this seems still marked as experimental, and doesn't support
> exception handling (which is a requirement for my language). And because my
> language uses return barriar
> (http://lists.llvm.org/pipermail/llvm-dev/2017-August/116291.html), I'm
> already using a new intrinsic that returns a token type for calls so I can
> have multiple return paths that retrieves the actual result, and currently
> it doesn't work with gc.statepoint.
>
> I wanna check the status of statepoint GC: Is it still actively developed?
> is there any plan to fix the exception handling path? Or should I continue
> to use the gcroot intrinsic? Change my new multi-return intrinsic to
support
> statepoint?
>
> I'm also thinking using a non-relocating GC with stackmap because
relocating
> is currently optional for me: all live roots are passed to call site as
> operand bundle, so codegen can emit the stack map, and my new intrinsic for
> multiple return paths can also work with that.
>
> Any advise will be welcome.
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

Returning to an ancient thread.  Sorry for the prolonged lack of response.

gc.statepoint is supported and actively developed.  The only production 
usage of LLVM's GC support I'm aware of is using gc.statepoint.  I 
recommend you use gc.statepoint, not gcroot.

I recently made a set of documentation edits which may provide some 
useful guidance for your non-relocating collector design. I'd be curious 
to know what you've settled on and what progress you've made.

Philip


On 12/8/17 1:29 PM, Chuan Qiu via llvm-dev wrote:
> Hi Team,
> I'm working on a new pure functional language and I'm trying to add
GC
> support for that.
>
> Because all vars are immutable, the IR that my frontend generates are 
> all register based, i.e. no alloca, and no readmem, writemem unless 
> accessing/constructing structs.
>
> If I use the traditional GC with gcroot intrinsic, it will need to 
> emit more code for liveness tracking, storing the IR values into the 
> gcroot, which seems convoluted.
>
> I found using stack map / statepoints very plausible here, because it 
> only needs all live vars without saving it to a corresponding gcroot, 
> and can track liveness at every call point.
>
> However, this seems still marked as experimental, and doesn't support 
> exception handling (which is a requirement for my language). And 
> because my language uses return barriar 
> (http://lists.llvm.org/pipermail/llvm-dev/2017-August/116291.html), 
> I'm already using a new intrinsic that returns a token type for calls 
> so I can have multiple return paths that retrieves the actual result, 
> and currently it doesn't work with gc.statepoint.
>
> I wanna check the status of statepoint GC: Is it still actively 
> developed? is there any plan to fix the exception handling path? Or 
> should I continue to use the gcroot intrinsic? Change my new 
> multi-return intrinsic to support statepoint?
>
> I'm also thinking using a non-relocating GC with stackmap because 
> relocating is currently optional for me: all live roots are passed to 
> call site as operand bundle, so codegen can emit the stack map, and my 
> new intrinsic for multiple return paths can also work with that.
>
> Any advise will be welcome.
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Thanks for reviving this.
I completely forgot the details but I resolved this problem. Looking though
the code, seems I forked RewriteStatepointsForGC pass, and change it to
adding 'gc-livevars' bundle to the call/invoke inst after finding the
livevars, instead of changing it to StatepointCall intrinsic.

On Wed, Nov 14, 2018 at 11:48 AM Philip Reames <listmail at
philipreames.com>
wrote:
> Returning to an ancient thread.  Sorry for the prolonged lack of response.
>
> gc.statepoint is supported and actively developed.  The only production
> usage of LLVM's GC support I'm aware of is using gc.statepoint.  I
> recommend you use gc.statepoint, not gcroot.
>
> I recently made a set of documentation edits which may provide some useful
> guidance for your non-relocating collector design.  I'd be curious to
know
> what you've settled on and what progress you've made.
>
> Philip
>
>
> On 12/8/17 1:29 PM, Chuan Qiu via llvm-dev wrote:
>
> Hi Team,
> I'm working on a new pure functional language and I'm trying to add
GC
> support for that.
>
> Because all vars are immutable, the IR that my frontend generates are all
> register based, i.e. no alloca, and no readmem, writemem unless
> accessing/constructing structs.
>
> If I use the traditional GC with gcroot intrinsic, it will need to emit
> more code for liveness tracking, storing the IR values into the gcroot,
> which seems convoluted.
>
> I found using stack map / statepoints very plausible here, because it only
> needs all live vars without saving it to a corresponding gcroot, and can
> track liveness at every call point.
>
> However, this seems still marked as experimental, and doesn't support
> exception handling (which is a requirement for my language). And because my
> language uses return barriar (
> http://lists.llvm.org/pipermail/llvm-dev/2017-August/116291.html), I'm
> already using a new intrinsic that returns a token type for calls so I can
> have multiple return paths that retrieves the actual result, and currently
> it doesn't work with gc.statepoint.
>
> I wanna check the status of statepoint GC: Is it still actively developed?
> is there any plan to fix the exception handling path? Or should I continue
> to use the gcroot intrinsic? Change my new multi-return intrinsic to
> support statepoint?
>
> I'm also thinking using a non-relocating GC with stackmap because
> relocating is currently optional for me: all live roots are passed to call
> site as operand bundle, so codegen can emit the stack map, and my new
> intrinsic for multiple return paths can also work with that.
>
> Any advise will be welcome.
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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