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[wasm-split] Remove dead globals #8505

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Merged
aheejin merged 3 commits into from
Mar 21, 2026
+30 −4
Merged

[wasm-split] Remove dead globals #8505

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2579712
[wasm-split] Remove dead globals
aheejin Mar 21, 2026
f66e325
Update src/ir/module-splitting.cpp
aheejin Mar 21, 2026
a0ee6dd
Update example test expectations
aheejin Mar 21, 2026
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15 changes: 13 additions & 2 deletions src/ir/module-splitting.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1182,8 +1182,18 @@ void ModuleSplitter::shareImportableItems() {

auto usingSecondaries =
getUsingSecondaries(global->name, &UsedNames::globals);
bool usedInPrimary = primaryUsed.globals.count(global->name);
if (!usedInPrimary && usingSecondaries.size() == 1) {
bool inPrimary = primaryUsed.globals.count(global->name);

if (!inPrimary && usingSecondaries.empty()) {
// It's not used anywhere, so delete it. Unlike other unused module items
// (memories, tables, and tags) that can just sit in the primary module
// and later be DCE'ed by another pass, we should remove it here, because
// an unused global can contain an initialier that refers to another
// global that will be moved to a secondary module, like
// (global $unused i32 (global.get $a)) // $a is moved to a secondary
globalsToRemove.push_back(global->name);

} else if (!inPrimary && usingSecondaries.size() == 1) {
// We are moving this global to this secondary module
auto* secondary = usingSecondaries[0];
auto* secondaryGlobal = ModuleUtils::copyGlobal(global.get(), *secondary);
Expand Down Expand Up @@ -1213,6 +1223,7 @@ void ModuleSplitter::shareImportableItems() {
// function.
}
}

} else { // We are NOT moving this global to the secondary module
if (global->init) {
for (auto* ref : FindAll<RefFunc>(global->init).list) {
Expand Down
2 changes: 0 additions & 2 deletions test/example/module-splitting.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,6 @@ Keeping: <none>
After:
(module
(type $0 (func (param i32)))
(global $glob (mut i32) (i32.const 7))
(memory $mem 3 42 shared)
(table $tab 3 42 funcref)
(tag $e (type $0) (param i32))
Expand All @@ -46,7 +45,6 @@ After:
(type $0 (func (param i32)))
(import "env" "mem" (memory $mem 3 42 shared))
(import "env" "tab" (table $tab 3 42 funcref))
(import "env" "glob" (global $glob (mut i32)))
(import "env" "e" (tag $e (type $0) (param i32)))
)
Secondary:
Expand Down
12 changes: 12 additions & 0 deletions test/lit/wasm-split/ref.func.wast
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Expand Up @@ -45,6 +45,12 @@
;; PRIMARY-NEXT: (drop
;; PRIMARY-NEXT: (ref.func $trampoline_second)
;; PRIMARY-NEXT: )
;; PRIMARY-NEXT: (drop
;; PRIMARY-NEXT: (global.get $glob1)
;; PRIMARY-NEXT: )
;; PRIMARY-NEXT: (drop
;; PRIMARY-NEXT: (global.get $glob2)
;; PRIMARY-NEXT: )
;; PRIMARY-NEXT: )
(func $prime
(drop
Expand All @@ -53,6 +59,12 @@
(drop
(ref.func $second)
)
(drop
(global.get $glob1)
)
(drop
(global.get $glob2)
)
Comment on lines +62 to +67
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@aheejin aheejin Mar 21, 2026

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After this PR, glob1 and glob2 are dead and the test doesn't do the intended testing anymore, so we use them here in the primary function

)

;; SECONDARY: (type $0 (func))
Expand Down
5 changes: 5 additions & 0 deletions test/lit/wasm-split/transitive-globals.wast
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Expand Up @@ -34,6 +34,11 @@

;; SECONDARY: (global $d i32 (global.get $e))

;; This dead global is referring to a global ($a) that's moved to the
;; secondary module. This should be deleted.
;; PRIMARY-NOT: (global (global $dead i32 (global.get $a))
(global $dead i32 (global.get $a))

;; PRIMARY: (func $keep
;; PRIMARY-NEXT: (drop
;; PRIMARY-NEXT: (global.get $e)
Expand Down
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