| Issue |
53118
|
| Summary |
Suboptimal codegen for tail call followed by unreachable
|
| Labels |
backend:X86
|
| Assignees |
|
| Reporter |
hyeongyukim
|
Suboptimal code for tail call followed by unreachable
```
declare void @callee(i64)
define void @endswith_unreachable(i64 %0) {
tail call void @callee(i64 %0)
unreachable
}
define void @endswith_return(i64 %0) {
tail call void @callee(i64 %0)
ret void
}
```
This IR is compiled as below.
https://godbolt.org/z/G9jrEzYoW
```
endswith_unreachable: # @endswith_unreachable
push rax
call callee@PLT
endswith_return: # @endswith_return
jmp callee@PLT # TAILCALL
```
The function ends with `tail call` followed by `ret void` creates a tail call with `jmp.`
But when the function ends with `unreachable,` a `call` is created rather than a `tail call.`
I suggest changing from `call` to `tail call` even if the function ends with `unreachable.`
I found this issue while resolving the objtool's (linux kernel's tool) warning for [D105169](https://reviews.llvm.org/D105169).
If you want to check the original problem, you can find the reduced version of the kernel code at https://godbolt.org/z/sYxTsnh5K and generated IR code containing `unreachable` at https://alive2.llvm.org/ce/z/szhgAB.
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