Skip to content

GlobalStructInference: Fix trivial packed fields and un-nest them too #8012

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 2 commits into from
Oct 31, 2025
Merged

GlobalStructInference: Fix trivial packed fields and un-nest them too #8012

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
36222ee
fix
kripken Oct 30, 2025
949d29b
Fix reads of null descriptors, with a cast
kripken Oct 31, 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
121 changes: 65 additions & 56 deletions src/passes/GlobalStructInference.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -351,13 +351,10 @@ struct GlobalStructInference : public Pass {
if (!global->mutable_ && !global->imported()) {
if (auto* structNew = global->init->dynCast<StructNew>()) {
auto value = readFromStructNew(structNew, fieldIndex, field);
// TODO: handle non-constant values using unnesting, as below.
if (value.isConstant()) {
replaceCurrent(value.getConstant().makeExpression(wasm));
return;
}
// Otherwise, continue to try the main type-based optimization
// below.
// We know the exact global being read here.
value.globals.push_back(global->name);
replaceCurrent(getReadValue(value, fieldIndex, field, curr));
return;
}
}
}
Expand Down Expand Up @@ -433,52 +430,6 @@ struct GlobalStructInference : public Pass {
}
}

// Helper for optimization: Given a Value, returns what we should read
// for it.
auto getReadValue = [&](const Value& value) -> Expression* {
Expression* ret;
if (value.isConstant()) {
// This is known to be a constant, so simply emit an expression for
// that constant, and handle if the field is packed.
ret = value.getConstant().makeExpression(wasm);
if (field) {
ret = Bits::makePackedFieldGet(
ret, *field, curr->cast<StructGet>()->signed_, wasm);
}
} else {
// Otherwise, this is non-constant, so we are in the situation where
// we want to un-nest the value out of the struct.new it is in. Note
// that for later work, as we cannot add a global in parallel.

// There can only be one global in a value that is not constant,
// which is the global we want to read from.
assert(value.globals.size() == 1);

// Create a global.get with temporary name, leaving only the
// updating of the name to later work.
auto* get = builder.makeGlobalGet(value.globals[0],
value.getExpression()->type);

globalsToUnnest.emplace_back(
GlobalToUnnest{value.globals[0], fieldIndex, get});

ret = get;
}

// If the type is more refined, we must refinalize. For example, we
// might have a struct.get that normally returns anyref, and know that
// field contains null, so we return nullref.
if (ret->type != curr->type) {
refinalize = true;
}

// This value replaces the struct.get, so it should have the same
// source location.
debuginfo::copyOriginalToReplacement(curr, ret, getFunction());

return ret;
};

// We have some globals (at least 2), and so must have at least one
// value. And we have already exited if we have more than 2 values (see
// the early return above) so that only leaves 1 and 2.
Expand All @@ -489,7 +440,7 @@ struct GlobalStructInference : public Pass {
// not need a fence.
replaceCurrent(builder.makeSequence(
builder.makeDrop(builder.makeRefAs(RefAsNonNull, ref)),
getReadValue(values[0])));
getReadValue(values[0], fieldIndex, field, curr)));
return;
}
assert(values.size() == 2);
Expand All @@ -513,8 +464,8 @@ struct GlobalStructInference : public Pass {
auto checkGlobal = values[0].globals[0];
// Compute the left and right values before the next line, as the order
// of their execution matters (they may note globals for un-nesting).
auto* left = getReadValue(values[0]);
auto* right = getReadValue(values[1]);
auto* left = getReadValue(values[0], fieldIndex, field, curr);
auto* right = getReadValue(values[1], fieldIndex, field, curr);
// Note that we must trap on null, so add a ref.as_non_null here. As
// before, the get cannot have synchronized with anything.
Expression* getGlobal =
Expand Down Expand Up @@ -556,6 +507,64 @@ struct GlobalStructInference : public Pass {
}
return value;
}

// Given a Value, returns what we should read for it.
Expression* getReadValue(const Value& value,
Index fieldIndex,
std::optional<Field>& field,
Expression* curr) {
auto& wasm = *getModule();
Builder builder(wasm);

Expression* ret;
if (value.isConstant()) {
// This is known to be a constant, so simply emit an expression for
// that constant, and handle if the field is packed.
ret = value.getConstant().makeExpression(wasm);
if (field) {
ret = Bits::makePackedFieldGet(
ret, *field, curr->cast<StructGet>()->signed_, wasm);
}
} else {
// Otherwise, this is non-constant, so we are in the situation where
// we want to un-nest the value out of the struct.new it is in. Note
// that for later work, as we cannot add a global in parallel.

// There can only be one global in a value that is not constant,
// which is the global we want to read from.
assert(value.globals.size() == 1);

// Create a global.get with temporary name, leaving only the
// updating of the name to later work.
auto* get = builder.makeGlobalGet(value.globals[0],
value.getExpression()->type);

globalsToUnnest.emplace_back(
GlobalToUnnest{value.globals[0], fieldIndex, get});

ret = get;
}

// We must add a cast to non-null in some cases: A read of a null
// descriptor returns a non-null value, so if there was a null in the
// global, that would not validate by itself.
if (ret->type.isNullable() && curr->type.isNonNullable()) {
ret = builder.makeRefAs(RefAsNonNull, ret);
}

// If the type is more refined, we must refinalize. For example, we
// might have a struct.get that normally returns anyref, and know that
// field contains null, so we return nullref.
if (ret->type != curr->type) {
refinalize = true;
}

// This value replaces the struct.get, so it should have the same
// source location.
debuginfo::copyOriginalToReplacement(curr, ret, getFunction());

return ret;
}
};

// Find the optimization opportunitites in parallel.
Expand Down
75 changes: 69 additions & 6 deletions test/lit/passes/gsi-nontype.wast
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -103,8 +103,8 @@
)
)

;; As above, but the value in the struct.new is not constant, so we cannot
;; optimize.
;; As above, but the value in the struct.new is not constant. We must un-nest
;; it into another global.
(module
;; CHECK: (type $table (struct (field anyref)))
(type $table (struct anyref))
Expand All @@ -114,8 +114,10 @@
;; CHECK: (import "a" "b" (global $imported funcref))
(import "a" "b" (global $imported funcref))

;; CHECK: (global $table.unnested.0 (ref (exact $table)) (struct.new_default $table))

;; CHECK: (global $table (ref $table) (struct.new $table
;; CHECK-NEXT: (struct.new_default $table)
;; CHECK-NEXT: (global.get $table.unnested.0)
;; CHECK-NEXT: ))
(global $table (ref $table)
(struct.new $table
Expand All @@ -125,9 +127,7 @@

;; CHECK: (func $test (type $1)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (struct.get $table 0
;; CHECK-NEXT: (global.get $table)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $table.unnested.0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test
Expand Down Expand Up @@ -204,3 +204,66 @@
)
)

;; A packed field.
(module
;; CHECK: (type $A (struct (field i8)))
(type $A (struct (field i8)))

;; CHECK: (type $1 (func))

;; CHECK: (global $global (ref $A) (struct.new $A
;; CHECK-NEXT: (i32.const -1)
;; CHECK-NEXT: ))
(global $global (ref $A) (struct.new $A
(i32.const -1)
))

;; CHECK: (func $test (type $1)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (i32.and
;; CHECK-NEXT: (i32.const -1)
;; CHECK-NEXT: (i32.const 255)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test
;; This should be 255, not -1.
(drop
(struct.get_u $A 0
(global.get $global)
)
)
)
)

;; When reading a null descriptor, we must cast to non-null.
(module
(rec
;; CHECK: (rec
;; CHECK-NEXT: (type $A (sub (descriptor $A.desc (struct))))
(type $A (sub (descriptor $A.desc (struct))))
;; CHECK: (type $A.desc (sub (describes $A (struct))))
(type $A.desc (sub (describes $A (struct))))
)

;; CHECK: (type $2 (func (result (ref $A.desc))))

;; CHECK: (global $global (ref $A) (struct.new_default $A
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: ))
(global $global (ref $A) (struct.new_default $A
(ref.null none)
))

;; CHECK: (func $test (type $2) (result (ref $A.desc))
;; CHECK-NEXT: (ref.as_non_null
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test (result (ref $A.desc))
(ref.get_desc $A
(global.get $global)
)
)
)

Loading