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PostEmscripten: Preserve __em_js__ exports (and data) in side modules #5780

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Jun 23, 2023
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PostEmscripten: Preserve __em_js__ exports (and data) in side modules #5780

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14 changes: 10 additions & 4 deletions src/passes/PostEmscripten.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -186,10 +186,13 @@ IString EM_JS_PREFIX("__em_js__");
IString EM_JS_DEPS_PREFIX("__em_lib_deps_");

struct EmJsWalker : public PostWalker<EmJsWalker> {
bool sideModule;
std::vector<Export> toRemove;

EmJsWalker(bool sideModule) : sideModule(sideModule) {}

void visitExport(Export* curr) {
if (curr->name.startsWith(EM_JS_PREFIX)) {
if (!sideModule && curr->name.startsWith(EM_JS_PREFIX)) {
toRemove.push_back(*curr);
}
if (curr->name.startsWith(EM_JS_DEPS_PREFIX)) {
Expand All @@ -215,14 +218,15 @@ struct PostEmscripten : public Pass {
auto& options = getPassOptions();
auto sideModule = options.hasArgument("post-emscripten-side-module");
if (!sideModule) {
removeData(module, segmentOffsets, "__start_em_asm", "__stop_em_asm");
removeData(module, segmentOffsets, "__start_em_js", "__stop_em_js");

// Side modules read EM_ASM data from the module based on these exports
// so we need to keep them around in that case.
removeData(module, segmentOffsets, "__start_em_asm", "__stop_em_asm");
module.removeExport("__start_em_asm");
module.removeExport("__stop_em_asm");
}

removeData(module, segmentOffsets, "__start_em_js", "__stop_em_js");
removeData(
module, segmentOffsets, "__start_em_lib_deps", "__stop_em_lib_deps");
module.removeExport("__start_em_js");
Expand All @@ -232,7 +236,9 @@ struct PostEmscripten : public Pass {
}

void removeEmJsExports(Module& module) {
EmJsWalker walker;
auto& options = getPassOptions();
auto sideModule = options.hasArgument("post-emscripten-side-module");
EmJsWalker walker(sideModule);
walker.walkModule(&module);
for (const Export& exp : walker.toRemove) {
if (exp.kind == ExternalKind::Function) {
Expand Down
49 changes: 49 additions & 0 deletions test/lit/passes/post-emscripten-side-module.wast
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@@ -0,0 +1,49 @@
;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
;; RUN: wasm-opt %s --post-emscripten --pass-arg=post-emscripten-side-module -S -o - | filecheck %s

;; Checks that the __start_em_asm/__stop_em_asm are preserverd, along with
;; all __em_js__ exports.

(module
;; CHECK: (global $em_asm_start i32 (i32.const 1000))
(global $em_asm_start i32 (i32.const 1000))
;; CHECK: (global $em_asm_stop i32 (i32.const 1011))
(global $em_asm_stop i32 (i32.const 1011))
;; CHECK: (global $em_js_start i32 (i32.const 2006))
(global $em_js_start i32 (i32.const 2006))
;; CHECK: (global $em_js_stop i32 (i32.const 2015))
(global $em_js_stop i32 (i32.const 2015))
;; CHECK: (global $__em_js__foo i32 (i32.const 2015))
(global $__em_js__foo i32 (i32.const 2015))
;; CHECK: (global $em_lib_deps_start i32 (i32.const 3000))
(global $em_lib_deps_start i32 (i32.const 3000))
;; CHECK: (global $em_lib_deps_stop i32 (i32.const 3009))
(global $em_lib_deps_stop i32 (i32.const 3009))
;; CHECK: (global $foo_start i32 (i32.const 4000))
(global $foo_start i32 (i32.const 4000))
;; CHECK: (global $foo_stop i32 (i32.const 4015))
(global $foo_stop i32 (i32.const 4015))
(memory 10 10)
;; CHECK: (memory $0 10 10)

;; CHECK: (data $data1 (i32.const 1000) "hello world")
(data $data1 (i32.const 1000) "hello world")
;; CHECK: (data $data2 (i32.const 2000) "hello DELETE ME world")
(data $data2 (i32.const 2000) "hello DELETE ME world")
;; CHECK: (data $data3 (i32.const 3000) "")
(data $data3 (i32.const 3000) "some deps")
;; CHECK: (export "__start_em_asm" (global $em_asm_start))
(export "__start_em_asm" (global $em_asm_start))
;; CHECK: (export "__stop_em_asm" (global $em_asm_stop))
(export "__stop_em_asm" (global $em_asm_stop))
(export "__start_em_js" (global $em_js_start))
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Why is this one not preserved in the output?

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For EM_ASM we use the global start/stop symbols and split the resulting string on NULL.

For EM_JS each string is exported via its own global export e.g. __em_js__foo so we don't need the start/stop symbols.

(export "__stop_em_js" (global $em_js_stop))
;; CHECK: (export "__em_js__foo" (global $__em_js__foo))
(export "__em_js__foo" (global $__em_js__foo))
(export "__start_em_lib_deps" (global $em_lib_deps_start))
(export "__stop_em_lib_deps" (global $em_lib_deps_stop))
;; CHECK: (export "__start_foo" (global $foo_start))
(export "__start_foo" (global $foo_start))
;; CHECK: (export "__stop_foo" (global $foo_stop))
(export "__stop_foo" (global $foo_stop))
)
1 change: 0 additions & 1 deletion test/lit/passes/post-emscripten.wast
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Expand Up @@ -41,4 +41,3 @@
;; CHECK: (export "__stop_foo" (global $foo_stop))
(export "__stop_foo" (global $foo_stop))
)