Skip to content

[Custom Descriptors] Handle inexact ref.get_desc in AbstractTypeRefining #7965

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Oct 10, 2025
Merged

[Custom Descriptors] Handle inexact ref.get_desc in AbstractTypeRefining #7965

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
1f47cbf
start
kripken Oct 10, 2025
ca8ba07
go
kripken Oct 10, 2025
bcaf232
finish
kripken Oct 10, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
25 changes: 19 additions & 6 deletions src/passes/AbstractTypeRefining.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -395,19 +395,32 @@ struct AbstractTypeRefining : public Pass {
}

// If we optimize away a descriptor type, then we must fix up any
// ref.get_desc of it, as ReFinalize would fix us up to return it. This
// can only happen when no such descriptor is created, which means the
// instruction will never be reached (no struct with such a descriptor was
// created).
// ref.get_desc of it, as ReFinalize would fix us up to return it.
void visitRefGetDesc(RefGetDesc* curr) {
auto optimized = getOptimized(curr->type);
if (!optimized) {
return;
}

// We are optimizing the descriptor to a subtype.
auto subDescriptor = *optimized;

Builder builder(*getModule());
replaceCurrent(builder.makeSequence(builder.makeDrop(curr->ref),
builder.makeUnreachable()));
if (curr->type.isExact() || subDescriptor == HeapTypes::none) {
// This is exact, so we can ignore subtypes, or there is no subtype to
// optimize to. In this case it must trap.
replaceCurrent(builder.makeSequence(builder.makeDrop(curr->ref),
builder.makeUnreachable()));
} else {
// The descriptor is abstract, but it has a subtype that is not
// (which we want to optimize to). We know this will only succeed if
// we receive the subtype of the described type, so that that
// descriptor is fetched. Add a cast so that we validate.
Copy link
Member

@tlively tlively Oct 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

As a follow-up, we can get rid of this cast (and if I'm not mistaken, this entire visitor) by inferring that a described type must not be instantiated if its descriptor type is uninstantiated.

Copy link
Member Author

@kripken kripken Oct 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I was thinking that, yeah, we can infer abstractness from descriptors to described...

Copy link
Member Author

@kripken kripken Oct 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I suspect though that other optimizations handle this (if the descriptor is not instantiated, eventually we infer all creations of the described receive null descriptors and hence trap, get removed, and the type becomes abstract).

Copy link
Member

@tlively tlively Oct 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yep, but I think cutting down on the iterations required to reach a good state is still useful, especially when it can make our code simpler as well.

auto subDescribed = subDescriptor.getDescribedType();
assert(subDescribed);
curr->ref =
builder.makeRefCast(curr->ref, curr->ref->type.with(*subDescribed));
}
}

void visitBrOn(BrOn* curr) {
Expand Down
124 changes: 124 additions & 0 deletions test/lit/passes/abstract-type-refining-desc.wast
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1038,6 +1038,8 @@

;; YESTNH: (type $2 (func (result (ref none))))

;; YESTNH: (type $3 (func (param (ref $A)) (result (ref none))))

;; YESTNH: (func $test (type $2) (result (ref none))
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (struct.new_default $A
Expand All @@ -1048,6 +1050,8 @@
;; YESTNH-NEXT: )
;; NO_TNH: (type $2 (func (result (ref none))))

;; NO_TNH: (type $3 (func (param (ref $A)) (result (ref none))))

;; NO_TNH: (func $test (type $2) (result (ref none))
;; NO_TNH-NEXT: (drop
;; NO_TNH-NEXT: (struct.new_default $A
Expand All @@ -1063,5 +1067,125 @@
)
)
)

;; YESTNH: (func $inexact (type $3) (param $inexact (ref $A)) (result (ref none))
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (local.get $inexact)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: (unreachable)
;; YESTNH-NEXT: )
;; NO_TNH: (func $inexact (type $3) (param $inexact (ref $A)) (result (ref none))
;; NO_TNH-NEXT: (drop
;; NO_TNH-NEXT: (local.get $inexact)
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: (unreachable)
;; NO_TNH-NEXT: )
(func $inexact (param $inexact (ref $A)) (result (ref $B))
;; As above, but now the input type is inexact. There are no subtypes, so
;; we still optimize.
(ref.get_desc $A
(local.get $inexact)
)
)
)

(module
;; As above, but now there are subtypes $A.sub, $B.sub.
(rec
;; YESTNH: (rec
;; YESTNH-NEXT: (type $A (sub (descriptor $B (struct))))
;; NO_TNH: (rec
;; NO_TNH-NEXT: (type $A (sub (descriptor $B (struct))))
(type $A (sub (descriptor $B (struct))))
;; YESTNH: (type $B (sub (describes $A (struct))))
;; NO_TNH: (type $B (sub (describes $A (struct))))
(type $B (sub (describes $A (struct))))

;; YESTNH: (type $A.sub (sub $A (descriptor $B.sub (struct))))
;; NO_TNH: (type $A.sub (sub $A (descriptor $B.sub (struct))))
(type $A.sub (sub $A (descriptor $B.sub (struct))))
;; YESTNH: (type $B.sub (sub $B (describes $A.sub (struct))))
;; NO_TNH: (type $B.sub (sub $B (describes $A.sub (struct))))
(type $B.sub (sub $B (describes $A.sub (struct))))
)

;; YESTNH: (type $4 (func))

;; YESTNH: (type $5 (func (result (ref (exact $B.sub)))))

;; YESTNH: (type $6 (func (param (ref $A)) (result (ref $B.sub))))

;; YESTNH: (func $create (type $4)
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (struct.new_default $A.sub
;; YESTNH-NEXT: (struct.new_default $B.sub)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (type $4 (func))

;; NO_TNH: (type $5 (func (result (ref (exact $B)))))

;; NO_TNH: (type $6 (func (param (ref $A)) (result (ref $B))))

;; NO_TNH: (func $create (type $4)
;; NO_TNH-NEXT: (drop
;; NO_TNH-NEXT: (struct.new_default $A.sub
;; NO_TNH-NEXT: (struct.new_default $B.sub)
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
(func $create
;; Make the subtypes not abstract.
(drop
(struct.new_default $A.sub
(struct.new_default $B.sub)
)
)
)

;; YESTNH: (func $test (type $5) (result (ref (exact $B.sub)))
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (struct.new_default $A
;; YESTNH-NEXT: (ref.null none)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: (unreachable)
;; YESTNH-NEXT: )
;; NO_TNH: (func $test (type $5) (result (ref (exact $B)))
;; NO_TNH-NEXT: (ref.get_desc $A
;; NO_TNH-NEXT: (struct.new_default $A
;; NO_TNH-NEXT: (ref.null none)
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
(func $test (result (ref (exact $B)))
;; We can still optimize here, thanks to exactness (when TNH).
(ref.get_desc $A
(struct.new_default $A
(ref.null none)
)
)
)

;; YESTNH: (func $inexact (type $6) (param $inexact (ref $A)) (result (ref $B.sub))
;; YESTNH-NEXT: (ref.get_desc $A.sub
;; YESTNH-NEXT: (ref.cast (ref $A.sub)
;; YESTNH-NEXT: (local.get $inexact)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $inexact (type $6) (param $inexact (ref $A)) (result (ref $B))
;; NO_TNH-NEXT: (ref.get_desc $A
;; NO_TNH-NEXT: (local.get $inexact)
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
(func $inexact (param $inexact (ref $A)) (result (ref $B))
;; We do not optimize to an unreachable here, as the inexact reference may
;; contain an $A.sub. We optimize to that, using a cast (in TNH).
(ref.get_desc $A
(local.get $inexact)
)
)
)

Loading