[wasm-split] Split globals' transitive global dependencies#8442
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aheejin wants to merge 1 commit intowasm_split_globalfrom
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[wasm-split] Split globals' transitive global dependencies#8442aheejin wants to merge 1 commit intowasm_split_globalfrom
aheejin wants to merge 1 commit intowasm_split_globalfrom
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When a global is exclusively used by a secondary module, we can move it to the secondary module. If its initializer contains a `global.get` of another global, we exported it from the primary module to the secondary module, even if it may not be used anywhere else. When we split a global out to a secondary module, this PR computes the transitive dependency of the split global, and if those globals in the dependency are not used anywhere else in other modules, we move them to the secondary module as well. #8441 and this PR combined reduce the size of the primary module by 29%. The running time of `wasm-split` hasn't really changed with this PR, compared to #8441. --- `wasm-objdump -h` result: - Before (#8441) ``` Type start=0x0000000c end=0x00035d44 (size=0x00035d38) count: 11185 Import start=0x00035d49 end=0x003faf6f (size=0x003c5226) count: 56805 Function start=0x003faf73 end=0x0040de1f (size=0x00012eac) count: 62890 Table start=0x0040de22 end=0x0041195d (size=0x00003b3b) count: 2921 Tag start=0x0041195f end=0x00411963 (size=0x00000004) count: 1 Global start=0x00411967 end=0x005541c5 (size=0x0014285e) count: 47771 Export start=0x005541ca end=0x007c0a00 (size=0x0026c836) count: 59077 Start start=0x007c0a02 end=0x007c0a04 (size=0x00000002) start: 828 Elem start=0x007c0a08 end=0x0082a84b (size=0x00069e43) count: 12303 DataCount start=0x0082a84d end=0x0082a84e (size=0x00000001) count: 1 Code start=0x0082a853 end=0x00a5a159 (size=0x0022f906) count: 62890 Data start=0x00a5a15d end=0x00a79cea (size=0x0001fb8d) count: 1 ``` - After (This PR) ``` Type start=0x0000000c end=0x00035d44 (size=0x00035d38) count: 11185 Import start=0x00035d48 end=0x00132efc (size=0x000fd1b4) count: 32642 Function start=0x00132f00 end=0x00145dac (size=0x00012eac) count: 62890 Table start=0x00145daf end=0x001498ea (size=0x00003b3b) count: 2921 Tag start=0x001498ec end=0x001498f0 (size=0x00000004) count: 1 Global start=0x001498f4 end=0x00289e60 (size=0x0014056c) count: 47728 Export start=0x00289e65 end=0x004977fe (size=0x0020d999) count: 35861 Start start=0x00497800 end=0x00497802 (size=0x00000002) start: 828 Elem start=0x00497806 end=0x00501649 (size=0x00069e43) count: 12303 DataCount start=0x0050164b end=0x0050164c (size=0x00000001) count: 1 Code start=0x00501651 end=0x00730f22 (size=0x0022f8d1) count: 62890 Data start=0x00730f26 end=0x00750ab3 (size=0x0001fb8d) count: 1 ``` Note that while the decrease in the global section is small, we have a significant size decrease in the import and the export sections, because we used to import globals and export them just to relay those globals to the secondary modules.
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When a global is exclusively used by a secondary module and thus moved to that module, and its initializer has a `(ref.func $func)`, we used to create a trampoline and export it from the primary module in all cases, even in the case that the function is in the same secondary module. This now moves those functions referred to by `ref.func`s to the secondary module, as long as they don't have uses anywhere else. To do this, we now skip scanning global initializers in `indirectReferencesToSecondaryFunctions`, and selectively create trampolines only when needed in `shareImportableItems`. The running time of `wasm-split` hasn't really changed with this PR, compared to the previous PR #8442 (~25s range in acx_gallery). #8441, #8442, and this PR combined reduce the size of the primary module by 46.6%. --- `wasm-objdump -h` result: - Before (#8442) ``` Type start=0x0000000c end=0x00035d44 (size=0x00035d38) count: 11185 Import start=0x00035d48 end=0x00132efc (size=0x000fd1b4) count: 32642 Function start=0x00132f00 end=0x00145dac (size=0x00012eac) count: 62890 Table start=0x00145daf end=0x001498ea (size=0x00003b3b) count: 2921 Tag start=0x001498ec end=0x001498f0 (size=0x00000004) count: 1 Global start=0x001498f4 end=0x00289e60 (size=0x0014056c) count: 47728 Export start=0x00289e65 end=0x004977fe (size=0x0020d999) count: 35861 Start start=0x00497800 end=0x00497802 (size=0x00000002) start: 828 Elem start=0x00497806 end=0x00501649 (size=0x00069e43) count: 12303 DataCount start=0x0050164b end=0x0050164c (size=0x00000001) count: 1 Code start=0x00501651 end=0x00730f22 (size=0x0022f8d1) count: 62890 Data start=0x00730f26 end=0x00750ab3 (size=0x0001fb8d) count: 1 ``` - After (This PR) ``` Type start=0x0000000c end=0x00035d38 (size=0x00035d2c) count: 11185 Import start=0x00035d3c end=0x00132ef0 (size=0x000fd1b4) count: 32642 Function start=0x00132ef4 end=0x001436cc (size=0x000107d8) count: 53001 Table start=0x001436cf end=0x0014720a (size=0x00003b3b) count: 2921 Tag start=0x0014720c end=0x00147210 (size=0x00000004) count: 1 Global start=0x00147214 end=0x00287b75 (size=0x00140961) count: 47728 Export start=0x00287b79 end=0x002e703f (size=0x0005f4c6) count: 25972 Start start=0x002e7041 end=0x002e7043 (size=0x00000002) start: 828 Elem start=0x002e7047 end=0x00349aa7 (size=0x00062a60) count: 12303 DataCount start=0x00349aa9 end=0x00349aaa (size=0x00000001) count: 1 Code start=0x00349aaf end=0x00550a4e (size=0x00206f9f) count: 53001 Data start=0x00550a52 end=0x005705df (size=0x0001fb8d) count: 1 ``` We can see while the size of the function and the code sections have decreased, the big gains come from the decrease of the export section, which can contain long function names.
This was referenced Mar 10, 2026
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When a global is exclusively used by a secondary module, we can move it to the secondary module. If its initializer contains a
global.getof another global, we exported it from the primary module to the secondary module, even if it may not be used anywhere else.When we split a global out to a secondary module, this PR computes the transitive dependency of the split global, and if those globals in the dependency are not used anywhere else in other modules, we move them to the secondary module as well.
#8441 and this PR combined reduce the size of the primary module of acx_gallery by 42.6%.
The running time of
wasm-splithasn't really changed with this PR, compared to #8441.wasm-objdump -hresult:Note that while the decrease in the global section is small, we have a significant size decrease in the import and the export sections, because we used to import globals and export them just to relay those globals to the secondary modules.
Follow-up: #8443