[llvm-dev] Optimizing assembly generated for tail call

[Haoran Xu via llvm-dev]

Hello,

I recently found that LLVM generates sub-optimal assembly for a tail call
optimization case. Below is an example (https://godbolt.org/z/ao15xE):

> void g1();
> void g2();
> void f(bool v) {
>    if (v) {
>     g1();
>    } else {
>      g2();
>    }
> }
>
The assembly generated is as follow:

> f(bool): # @f(bool)
> testb %dil, %dil
> je .LBB0_2
> jmp g1() # TAILCALL
> .LBB0_2:
> jmp g2() # TAILCALL
>
However, in this specific case (where no function epilogue is needed), one
can actually change 'je .LBB0_2' to 'je g2()' directly, thus saving a jump.
Is there any way I could instruct LLVM to do this? For my use case, it is
acceptable to do this at any level (C++ level /IR level /MachineInst level
is all fine).

Thanks!

Best,
Haoran
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