[PATCH] D106426: [FuncSpec] Support specialising recursive functions

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

> If we run bin/opt -function-specialization -func-specialization-max-iters=10  -S %s, we could find that recursiveFunc would get specialized 18 times.

This is not not true. It will get specialised 10 times.

> Then I run bin/opt -function-specialization -func-specialization-max-iters=10 -inline -instcombine -simplifycfg -S %s, I got:
> <SNIP>
> hmmmm, I guess it must not be your expected code, right?

Hmmm, sorry, this is exactly what I expect. Look at the generated code:

  _main:                                  ; @main
        stp     x20, x19, [sp, #-32]!           ; 16-byte Folded Spill
        stp     x29, x30, [sp, #16]             ; 16-byte Folded Spill
        adrp    x19, _funcspec.arg.17 at PAGE
        add     x19, x19, _funcspec.arg.17 at PAGEOFF
  LBB1_1:
        mov     w0, #1
        bl      _print_val
  LBB1_2:
        mov     w0, #2
        bl      _print_val
  LBB1_3:
        mov     w0, #3
        bl      _print_val
  LBB1_4:
        mov     w0, #4
        bl      _print_val
  LBB1_5:
        mov     w0, #5
        bl      _print_val
  LBB1_6:
        mov     w0, #6
        bl      _print_val
  LBB1_7:
        mov     w0, #7
        bl      _print_val
  LBB1_8:
        mov     w0, #8
        bl      _print_val
  LBB1_9:
        mov     w0, #9
        bl      _print_val
        mov     x0, x19
        bl      _recursiveFunc
        bl      _exit_cond
        tbnz    w0, #0, LBB1_9
        bl      _exit_cond
        tbnz    w0, #0, LBB1_9
        bl      _exit_cond
        tbnz    w0, #0, LBB1_9
        bl      _exit_cond
        tbnz    w0, #0, LBB1_9
        bl      _exit_cond
        tbnz    w0, #0, LBB1_8
        bl      _exit_cond
        tbnz    w0, #0, LBB1_8
        bl      _exit_cond
        tbnz    w0, #0, LBB1_8
        bl      _exit_cond
        tbnz    w0, #0, LBB1_8
        bl      _exit_cond
        tbnz    w0, #0, LBB1_8
        bl      _exit_cond
        tbnz    w0, #0, LBB1_7
        bl      _exit_cond
        tbnz    w0, #0, LBB1_7
        bl      _exit_cond
        tbnz    w0, #0, LBB1_7
        bl      _exit_cond
        tbnz    w0, #0, LBB1_7
        bl      _exit_cond
        <SNIP: a few more>

That seem fairly optimal to me, so don't know why we wouldn't be doing this, or what we need to differently.

> I think all of them would be affected. The impact on code-size is obvious. For the compile-time, it would take a long time to compile if we set the argument  func-specialization-max-iters to 2000.

I am sorry, but this is an unreasonable number. There is no point in discussing such a big number, because the default will never be even close to that, and if you do want to set it to very high, then that's opt-in and your responsibility.


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  https://reviews.llvm.org/D106426/new/

https://reviews.llvm.org/D106426