Skip to content

Fix optimization of casts to exact null types #7365

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
tlively merged 1 commit into from
Mar 12, 2025
Merged

Fix optimization of casts to exact null types #7365

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
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
21 changes: 15 additions & 6 deletions src/passes/OptimizeInstructions.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2277,10 +2277,14 @@ struct OptimizeInstructions
// emit a null check.
bool needsNullCheck = ref->type.getNullability() == Nullable &&
curr->type.getNullability() == NonNullable;
// Same with exactness.
bool needsExactCast = ref->type.getExactness() == Inexact &&
curr->type.getExactness() == Exact;
// If the best value to propagate is the argument to the cast, we can
// simply remove the cast (or downgrade it to a null check if
// necessary).
if (ref == curr->ref) {
// necessary). This does not work if we need a cast to prove
// exactness.
if (ref == curr->ref && !needsExactCast) {
if (needsNullCheck) {
replaceCurrent(builder.makeRefAs(RefAsNonNull, curr->ref));
} else {
Expand All @@ -2289,17 +2293,22 @@ struct OptimizeInstructions
return;
}
// Otherwise we can't just remove the cast and replace it with `ref`
// because the intermediate expressions might have had side effects.
// We can replace the cast with a drop followed by a direct return of
// the value, though.
// because the intermediate expressions might have had side effects or
// we need to check exactness. We can replace the cast with a drop
// followed by a direct return of the value, though.
if (ref->type.isNull()) {
// TODO: Remove this once we type ref.null as exact.
if (needsExactCast) {
return;
}

// We can materialize the resulting null value directly.
//
// The type must be nullable for us to do that, which it normally
// would be, aside from the interesting corner case of
// uninhabitable types:
//
// (ref.cast func
// (ref.cast (ref func)
// (block (result (ref nofunc))
// (unreachable)
// )
Expand Down
30 changes: 19 additions & 11 deletions test/lit/passes/optimize-instructions-exact.wast
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,19 +6,27 @@
;; RUN: wasm-opt %s -all --optimize-instructions -S -o - | filecheck %s

(module
;; CHECK: (func $cast-to-exact-none (type $0) (param $0 anyref)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (ref.cast (exact nullref)
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK: (func $cast-any-to-exact-none (type $0) (param $0 anyref) (result (exact nullref))
;; CHECK-NEXT: (ref.cast (exact nullref)
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $cast-to-exact-none (param anyref)
(drop
;; This will not be changed, but should not trigger an assertion.
(ref.cast (exact nullref)
(local.get 0)
)
(func $cast-any-to-exact-none (param anyref) (result (exact nullref))
;; This will not be changed, but should not trigger an assertion.
(ref.cast (exact nullref)
(local.get 0)
)
)
;; CHECK: (func $cast-null-to-exact-none (type $1) (result (exact nullref))
;; CHECK-NEXT: (local $0 nullref)
;; CHECK-NEXT: (ref.cast (exact nullref)
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $cast-null-to-exact-none (result (exact nullref))
(local nullref)
(ref.cast (exact nullref)
(local.get 0)
)
)
)