[wasm-split] Move exclusive items to secondary modules

[aheejin]

When splitting a module, if non-function items (memories, tables, globals, tags) are exclusively used by a single secondary module, this moves them directly to that secondary module rather than exporting them from the primary module.

When a global is moved, its initializer can contain global.get or ref.funcs, creating dependences on other globals and functions. For now, this PR just exports all the dependences from the primary module to the secondary module. This will be improved by follow-up PRs.

This PR reduces the size of the primary module for acx_gallery by 12.5%. Follow-up PRs will reduce it further.

This also sadly increases wasm-split's running time on acx_gallery from 16.5s -> 24.7s, by 49%, due to more computations in shareImportableItems.

---

The below is wasm-objdump -h result of the primary modules:

• Before

     Type start=0x0000000c end=0x00035e09 (size=0x00035dfd) count: 11192
   Import start=0x00035e0e end=0x004bd669 (size=0x0048785b) count: 65720
 Function start=0x004bd66d end=0x004d0519 (size=0x00012eac) count: 62890
    Table start=0x004d051c end=0x004d4059 (size=0x00003b3d) count: 2921
      Tag start=0x004d405b end=0x004d405f (size=0x00000004) count: 1
   Global start=0x004d4063 end=0x00689ff8 (size=0x001b5f95) count: 80766
   Export start=0x00689ffc end=0x0071b16c (size=0x00091170) count: 60877
    Start start=0x0071b16e end=0x0071b170 (size=0x00000002) start: 828
     Elem start=0x0071b174 end=0x00784fb9 (size=0x00069e45) count: 12303
DataCount start=0x00784fbb end=0x00784fbc (size=0x00000001) count: 1
     Code start=0x00784fc1 end=0x009b4958 (size=0x0022f997) count: 62890
     Data start=0x009b495c end=0x009d44e9 (size=0x0001fb8d) count: 1

• After (This PR)

     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=0x005541c9 end=0x005dfc2c (size=0x0008ba63) count: 59077
    Start start=0x005dfc2e end=0x005dfc30 (size=0x00000002) start: 828
     Elem start=0x005dfc34 end=0x00649a77 (size=0x00069e43) count: 12303
DataCount start=0x00649a79 end=0x00649a7a (size=0x00000001) count: 1
     Code start=0x00649a7f end=0x00879385 (size=0x0022f906) count: 62890
     Data start=0x00879389 end=0x00898f16 (size=0x0001fb8d) count: 1

Follow-ups: #8442 and #8443

[aheejin]

cc @biggs0125

[tlively]

The reason is, while we shed some exports for globals, we gained exports for functions (due to globals ref.func dependences), which had a lot longer names.

I'm surprised the length of names factors into this. I thought we used minimized names for internal exports. Am I misremembering?

[aheejin]

Sorry, you're right, I was running the tests with -g option. (I was confused and I thought I needed that option to 'output' the name section, which was not true) This PR does not increase the size of the primary module.

I reran all tests for this and the two follow-up PRs and updated the PR description. The primary module size is

• This: -12.5%
• This + [wasm-split] Split globals' transitive global dependencies #8442: -42.6%
• This + [wasm-split] Split globals' transitive global dependencies #8442 + [wasm-split] Split globals' ref.func dependencies #8443: -45.4%