| Issue |
147201
|
| Summary |
[lld][WebAssembly] Linker relaxation: rewrite `global.get GOT.mem.value` to `i32.const <value>`
|
| Labels |
lld
|
| Assignees |
|
| Reporter |
SingleAccretion
|
As part of our compiler, we hand-emit a small number of helper methods in pure WASM, of a kind like below:
```c
void helper_11(arg1, arg2) {
extern int compiler_generated_data_symbol_11;
return SomeMethod(&compiler_generated_data_symbol_11, arg1, arg2);
}
```
Historically this was done without the need to consider `-fPIC`, but recently we've started thinking about supporting that too. However, we would also like to emit code that is "PIC-agnostic" (this is how the compiler works for other targets).
In a non-PIC build, the example from above will emit something like:
```
000042: 41 80 80 80 80 00 | i32.const 0
000043: R_WASM_MEMORY_ADDR_SLEB 1 <compiler_generated_data_symbol_11>
```
And that's also what we emit currently (more or less).
For "PIC-agnostic" code, we could emit the same using GOT, like so:
```
000053: 23 80 80 80 80 00 | global.get 0 <GOT.mem.compiler_generated_data_symbol_11>
000054: R_WASM_GLOBAL_INDEX_LEB 1 <compiler_generated_data_symbol_11>
```
To keep (roughly) the same code size and runtime performance. However, we will then have a bunch of immutable `GOT.*` globals that don't really serve much purpose in a non-PIE link.
But this seems avoidable if all the references to these `GOT` globals could be rewritten in-place to `i32.const`s with the actual value.
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