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[Custom Descriptors] Use exact imports in wasm-split #8043

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Merged
merged 4 commits into from
Nov 14, 2025
Merged

[Custom Descriptors] Use exact imports in wasm-split #8043

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e24f935
[Custom Descriptors] Exact imports require CD
tlively Nov 12, 2025
2ac622d
[Custom Descriptors] Use exact imports in wasm-split
tlively Nov 12, 2025
bc4f3ef
Merge branch 'main' into use-exact-func-imports
tlively Nov 14, 2025
ab06811
update tests
tlively Nov 14, 2025
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37 changes: 8 additions & 29 deletions src/ir/module-splitting.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,13 @@
// 2. It assumes that either all table segment offsets are constants or there
// is exactly one segment that may have a non-constant offset. It also
// assumes that all segments are active segments.

//
// 3. It assumes that if exact function references are required for validity
// (because they are stored in a local with an exact function type, for
// example), then custom descriptors are allowed so primary functions can
// be imported exactly. This could be worked around by removing exactness
// from the IR before splitting.
//
#include "ir/module-splitting.h"
#include "asmjs/shared-constants.h"
#include "ir/export-utils.h"
Expand Down Expand Up @@ -341,7 +347,6 @@ struct ModuleSplitter {
void setupTablePatching();
void shareImportableItems();
void removeUnusedSecondaryElements();
void updateIR();

ModuleSplitter(Module& primary, const Config& config)
: config(config), primary(primary), tableManager(primary),
Expand All @@ -358,7 +363,6 @@ struct ModuleSplitter {
setupTablePatching();
shareImportableItems();
removeUnusedSecondaryElements();
updateIR();
}
};

Expand Down Expand Up @@ -520,7 +524,7 @@ void ModuleSplitter::exportImportFunction(Name funcName,
func->hasExplicitName = primaryFunc->hasExplicitName;
func->module = config.importNamespace;
func->base = exportName;
func->type = func->type.with(Inexact);
func->type = func->type.withInexactIfNoCustomDescs(secondary->features);
secondary->addFunction(std::move(func));
}
}
Expand Down Expand Up @@ -981,31 +985,6 @@ void ModuleSplitter::removeUnusedSecondaryElements() {
}
}

void ModuleSplitter::updateIR() {
// Imported functions may need type updates.
struct Fixer : public PostWalker<Fixer> {
void visitRefFunc(RefFunc* curr) {
auto& wasm = *getModule();
auto* func = wasm.getFunction(curr->func);
if (func->type != curr->type) {
// This became an import, and lost exactness.
assert(!func->type.isExact());
assert(curr->type.isExact());
if (wasm.features.hasCustomDescriptors()) {
// Add a cast, as the parent may depend on the exactness to validate.
// TODO: The cast may be needed even without CD enabled
replaceCurrent(Builder(wasm).makeRefCast(curr, curr->type));
}
curr->type = curr->type.with(Inexact);
}
}
} fixer;
fixer.walkModule(&primary);
for (auto& secondaryPtr : secondaries) {
fixer.walkModule(secondaryPtr.get());
}
}

} // anonymous namespace

Results splitFunctions(Module& primary, const Config& config) {
Expand Down
6 changes: 5 additions & 1 deletion src/ir/module-splitting.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,14 +26,18 @@
// functions. The secondary module imports all of its dependencies from the
// primary module.
//
// This code currently makes a couple assumptions about the modules that will be
// This code currently makes a few assumptions about the modules that will be
// split and will fail assertions if those assumptions are not true.
//
// 1) It assumes that mutable-globals are allowed.
//
// 2) It assumes that either all segment offsets are constants or there is
// exactly one segment that may have a non-constant offset.
//
// 3) It assumes that exact function references are only required for validity
// if custom descriptors (and its exact function import feature) are
// allowed.
//
// These requirements will be relaxed as necessary in the future, but for now
// this code should be considered experimental and used with care.

Expand Down
6 changes: 3 additions & 3 deletions test/example/module-splitting.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -745,7 +745,7 @@ Secondary:
(module
(type $0 (func))
(import "primary" "%table" (table $0 1 funcref))
(import "primary" "%foo_1" (func $foo (type $0)))
(import "primary" "%foo_1" (func $foo (exact (type $0))))
(elem $0 (i32.const 0) $bar)
(func $bar (type $0)
(call $foo)
Expand Down Expand Up @@ -1055,7 +1055,7 @@ Secondary:
(module
(type $0 (func))
(import "primary" "%table_2" (table $0 1 funcref))
(import "primary" "%foo" (func $foo (type $0)))
(import "primary" "%foo" (func $foo (exact (type $0))))
(elem $0 (i32.const 0) $bar)
(func $bar (type $0)
(call $foo)
Expand Down Expand Up @@ -1102,7 +1102,7 @@ Secondary:
(module
(type $0 (func (param i32) (result i32)))
(import "primary" "%table_2" (table $0 1 funcref))
(import "primary" "%foo" (func $foo (type $0) (param i32) (result i32)))
(import "primary" "%foo" (func $foo (exact (type $0) (param i32) (result i32))))
(elem $0 (i32.const 0) $bar)
(func $bar (type $0) (param $0 i32) (result i32)
(call $foo
Expand Down
6 changes: 2 additions & 4 deletions test/lit/wasm-split/exact.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -73,7 +73,7 @@

;; SECONDARY: (import "primary" "table" (table $timport$0 1 funcref))

;; SECONDARY: (import "primary" "foo" (func $foo (type $0)))
;; SECONDARY: (import "primary" "foo" (func $foo (exact (type $0))))

;; SECONDARY: (elem $0 (i32.const 0) $bar)

Expand All @@ -82,9 +82,7 @@
;; SECONDARY: (func $bar (type $0)
;; SECONDARY-NEXT: (local $exact (ref (exact $0)))
;; SECONDARY-NEXT: (local.set $exact
;; SECONDARY-NEXT: (ref.cast (ref (exact $0))
;; SECONDARY-NEXT: (ref.func $foo)
;; SECONDARY-NEXT: )
;; SECONDARY-NEXT: (ref.func $foo)
;; SECONDARY-NEXT: )
;; SECONDARY-NEXT: (local.set $exact
;; SECONDARY-NEXT: (ref.func $bar)
Expand Down
36 changes: 12 additions & 24 deletions test/lit/wasm-split/multi-split-escape-names.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,9 @@

;; MOD1: (import "primary" "table" (table $timport$0 3 funcref))

;; MOD1: (import "primary" "trampoline_std::operator<<\\28std::__2::basic_ostream<char\\2c\\20std::__2::char_traits<char>>&\\2c\\20wasm::Module&\\29" (func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29 (result f32)))
;; MOD1: (import "primary" "trampoline_std::operator<<\\28std::__2::basic_ostream<char\\2c\\20std::__2::char_traits<char>>&\\2c\\20wasm::Module&\\29" (func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29 (exact (result f32))))

;; MOD1: (import "primary" "trampoline_wasm::Literal::Literal\\28std::__2::array<wasm::Literal\\2c\\204ul>\\20const&\\29" (func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29 (result i64)))
;; MOD1: (import "primary" "trampoline_wasm::Literal::Literal\\28std::__2::array<wasm::Literal\\2c\\204ul>\\20const&\\29" (func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29 (exact (result i64))))

;; MOD1: (elem $0 (i32.const 2) $wasm::Type::getFeatures\28\29\20const)

Expand All @@ -38,16 +38,12 @@
;; MOD1-NEXT: )
;; MOD1-NEXT: (drop
;; MOD1-NEXT: (call_ref $1
;; MOD1-NEXT: (ref.cast (ref (exact $1))
;; MOD1-NEXT: (ref.func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29)
;; MOD1-NEXT: )
;; MOD1-NEXT: (ref.func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29)
;; MOD1-NEXT: )
;; MOD1-NEXT: )
;; MOD1-NEXT: (drop
;; MOD1-NEXT: (call_ref $0
;; MOD1-NEXT: (ref.cast (ref (exact $0))
;; MOD1-NEXT: (ref.func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29)
;; MOD1-NEXT: )
;; MOD1-NEXT: (ref.func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29)
;; MOD1-NEXT: )
;; MOD1-NEXT: )
;; MOD1-NEXT: (i32.const 0)
Expand Down Expand Up @@ -79,18 +75,16 @@

;; MOD2: (import "primary" "table" (table $timport$0 3 funcref))

;; MOD2: (import "primary" "trampoline_std::operator<<\\28std::__2::basic_ostream<char\\2c\\20std::__2::char_traits<char>>&\\2c\\20wasm::Module&\\29" (func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29 (result f32)))
;; MOD2: (import "primary" "trampoline_std::operator<<\\28std::__2::basic_ostream<char\\2c\\20std::__2::char_traits<char>>&\\2c\\20wasm::Module&\\29" (func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29 (exact (result f32))))

;; MOD2: (import "primary" "trampoline_wasm::Type::getFeatures\\28\\29\\20const" (func $trampoline_wasm::Type::getFeatures\28\29\20const (result i32)))
;; MOD2: (import "primary" "trampoline_wasm::Type::getFeatures\\28\\29\\20const" (func $trampoline_wasm::Type::getFeatures\28\29\20const (exact (result i32))))

;; MOD2: (elem $0 (i32.const 0) $wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29)

;; MOD2: (func $wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29 (result i64)
;; MOD2-NEXT: (drop
;; MOD2-NEXT: (call_ref $1
;; MOD2-NEXT: (ref.cast (ref (exact $1))
;; MOD2-NEXT: (ref.func $trampoline_wasm::Type::getFeatures\28\29\20const)
;; MOD2-NEXT: )
;; MOD2-NEXT: (ref.func $trampoline_wasm::Type::getFeatures\28\29\20const)
;; MOD2-NEXT: )
;; MOD2-NEXT: )
;; MOD2-NEXT: (drop
Expand All @@ -100,9 +94,7 @@
;; MOD2-NEXT: )
;; MOD2-NEXT: (drop
;; MOD2-NEXT: (call_ref $0
;; MOD2-NEXT: (ref.cast (ref (exact $0))
;; MOD2-NEXT: (ref.func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29)
;; MOD2-NEXT: )
;; MOD2-NEXT: (ref.func $trampoline_std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29)
;; MOD2-NEXT: )
;; MOD2-NEXT: )
;; MOD2-NEXT: (i64.const 0)
Expand Down Expand Up @@ -134,25 +126,21 @@

;; MOD3: (import "primary" "table" (table $timport$0 3 funcref))

;; MOD3: (import "primary" "trampoline_wasm::Literal::Literal\\28std::__2::array<wasm::Literal\\2c\\204ul>\\20const&\\29" (func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29 (result i64)))
;; MOD3: (import "primary" "trampoline_wasm::Literal::Literal\\28std::__2::array<wasm::Literal\\2c\\204ul>\\20const&\\29" (func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29 (exact (result i64))))

;; MOD3: (import "primary" "trampoline_wasm::Type::getFeatures\\28\\29\\20const" (func $trampoline_wasm::Type::getFeatures\28\29\20const (result i32)))
;; MOD3: (import "primary" "trampoline_wasm::Type::getFeatures\\28\\29\\20const" (func $trampoline_wasm::Type::getFeatures\28\29\20const (exact (result i32))))

;; MOD3: (elem $0 (i32.const 1) $std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29)

;; MOD3: (func $std::operator<<\28std::__2::basic_ostream<char\2c\20std::__2::char_traits<char>>&\2c\20wasm::Module&\29 (result f32)
;; MOD3-NEXT: (drop
;; MOD3-NEXT: (call_ref $1
;; MOD3-NEXT: (ref.cast (ref (exact $1))
;; MOD3-NEXT: (ref.func $trampoline_wasm::Type::getFeatures\28\29\20const)
;; MOD3-NEXT: )
;; MOD3-NEXT: (ref.func $trampoline_wasm::Type::getFeatures\28\29\20const)
;; MOD3-NEXT: )
;; MOD3-NEXT: )
;; MOD3-NEXT: (drop
;; MOD3-NEXT: (call_ref $0
;; MOD3-NEXT: (ref.cast (ref (exact $0))
;; MOD3-NEXT: (ref.func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29)
;; MOD3-NEXT: )
;; MOD3-NEXT: (ref.func $trampoline_wasm::Literal::Literal\28std::__2::array<wasm::Literal\2c\204ul>\20const&\29)
;; MOD3-NEXT: )
;; MOD3-NEXT: )
;; MOD3-NEXT: (drop
Expand Down
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