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digitalmars.D - Wasm: druntime with full GC

reply "H. S. Teoh" <hsteoh qfbox.info> writes:
So I've been working on my minimal druntime for wasm, and discovered
that LLVM actually uses a shadow stack for wasm, not the native
non-addressable wasm stack. Which means that it's possible to scan the
(shadow) stack for GC roots. Which means, in theory, that the full
druntime *could* be ported to wasm, GC and all.

Of course, GC parameters would have to be tweaked in order to fit the
memory constraints of your typical wasm environment. And probably lots
of performance tweaking would be needed. But it'd work.

Which also means that we don't have to wait for WasmGC support to land
in llvm before we can target wasm. In an ideal world the host GC would
take care of providing GC services, but even today, what we have ought
to be enough to port the current D GC to wasm(!).

//

Porting the entirety of druntime to wasm is kinda way out of my scope
right now. I'll probably continue working on gradually expanding my
current minimal druntime to cover more and more of the language. It
might be a good opportunity to experiment with alternative GC schemes
too. I've started with a dumb bump-the-pointer allocator, and planning
to gradually expand it to full GC in the not-so-near future.  Maybe I'll
experiment with write barriers and incremental GCs as well, once I get
to that point...


T

-- 
Tell me and I forget. Teach me and I remember. Involve me and I understand. --
Benjamin Franklin
Feb 06
next sibling parent Denis Feklushkin <feklushkin.denis gmail.com> writes:
On Wednesday, 7 February 2024 at 03:52:15 UTC, H. S. Teoh wrote:


 Porting the entirety of druntime to wasm is kinda way out of my 
 scope right now. I'll probably continue working on gradually 
 expanding my current minimal druntime to cover more and more of 
 the language.


Maybe this will help: 
https://github.com/dlang/dmd/pull/15887#issuecomment-1925823060

This patch highlights minimal number of the druntime pieces that 
need to be changed for the another platform support
Feb 07
prev sibling parent reply Sebastiaan Koppe <mail skoppe.eu> writes:
On Wednesday, 7 February 2024 at 03:52:15 UTC, H. S. Teoh wrote:

 So I've been working on my minimal druntime for wasm, and 
 discovered that LLVM actually uses a shadow stack for wasm, not 
 the native non-addressable wasm stack.


It does for debug, but then the optimisations push a lot of that 
to the wasm stack, see mem2reg step in llvm.

A possibility is to run the spill-pointers pass of binaryen, that 
should hoist the pointers back out to the shadow stack. With some 
perf hit of course.
Feb 07
parent reply "H. S. Teoh" <hsteoh qfbox.info> writes:
On Wed, Feb 07, 2024 at 08:55:16PM +0000, Sebastiaan Koppe via Digitalmars-d
wrote:

 On Wednesday, 7 February 2024 at 03:52:15 UTC, H. S. Teoh wrote:

 So I've been working on my minimal druntime for wasm, and discovered
 that LLVM actually uses a shadow stack for wasm, not the native
 non-addressable wasm stack.


 
 It does for debug, but then the optimisations push a lot of that to
 the wasm stack, see mem2reg step in llvm.
 
 A possibility is to run the spill-pointers pass of binaryen, that
 should hoist the pointers back out to the shadow stack. With some perf
 hit of course.


Unfortunately, looks like my distro's version of binaryen doesn't
support --spill-pointers.


T

-- 
English is useful because it is a mess. Since English is a mess, it maps well
onto the problem space, which is also a mess, which we call reality. Similarly,
Perl was designed to be a mess, though in the nicest of all possible ways. --
Larry Wall
Feb 09
parent Sebastiaan Koppe <mail skoppe.eu> writes:
On Friday, 9 February 2024 at 17:23:17 UTC, H. S. Teoh wrote:

 Unfortunately, looks like my distro's version of binaryen 
 doesn't support --spill-pointers.


 T


Then install manually. I am sure they have releases or, if that 
fails, build instructions.
Feb 09