On Fri, Aug 22, 2025 at 4:04 PM Andrew Pinski
<andrew.pin...@oss.qualcomm.com> wrote:
>
> So the current pass order is:
> ```
> NEXT_PASS (pass_tail_recursion);
> NEXT_PASS (pass_if_to_switch);
> NEXT_PASS (pass_convert_switch);
> NEXT_PASS (pass_cleanup_eh);
> ```
> But nothing in if_to_switch nor convert_switch will change the IR
> such that cleanup eh will take into account.
> tail_recusion benifits the most by not having "almost" empty landing pads.
> This order was originally done when cleanup_eh was added in
> r0-92178-ga8da523f8a442f
> but it looks like it was just done just before inlining rather than thinking
> it
> could improve passes before hand.
>
> An example where this helps is PR 115201 where we have:
> ```
> ;; basic block 5, loop depth 0, maybe hot
> ;; prev block 4, next block 6, flags: (NEW, REACHABLE, VISITED)
> ;; pred: 4 (TRUE_VALUE,EXECUTABLE)
> [LP 1] # .MEM_19 = VDEF <.MEM_45>
> # USE = nonlocal escaped
> # CLB = nonlocal escaped
> D.4770 = _Z12binarySearchIi2itIiEET0_RKT_S2_S2_D.4690 (item_15(D),
> startD.4711, midD.4717);
> goto <bb 7>; [INV]
> ;; succ: 8 (EH,EXECUTABLE)
> ;; 7 (FALLTHRU,EXECUTABLE)
> ...
>
> ;; basic block 8, loop depth 0, maybe hot
> ;; prev block 7, next block 1, flags: (NEW, REACHABLE, VISITED)
> ;; pred: 5 (EH,EXECUTABLE)
> ;; 6 (EH,EXECUTABLE)
> # .MEM_7 = PHI <.MEM_19(5), .MEM_18(6)>
> <L6>: [LP 1]
> # .MEM_20 = VDEF <.MEM_7>
> midD.4717 ={v} {CLOBBER(eos)};
> resx 1
> ;; succ:
> ```
>
> As you can see the empty landing pad should be able to remove away and
> then a tail recursion can happen.
>
> Bootstrapped and tested x86_64-linux-gnu.
>
> PR tree-optimization/115201
> gcc/ChangeLog:
>
> * passes.def: Move cleanup_eh before first tail_recursion.
>
> Signed-off-by: Andrew Pinski <andrew.pin...@oss.qualcomm.com>
> ---
> gcc/passes.def | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/passes.def b/gcc/passes.def
> index 68ce53baa0f..6349abb5360 100644
> --- a/gcc/passes.def
> +++ b/gcc/passes.def
> @@ -97,10 +97,10 @@ along with GCC; see the file COPYING3. If not see
> NEXT_PASS (pass_dse);
> NEXT_PASS (pass_cd_dce, false /* update_address_taken_p */, true /*
> remove_unused_locals */);
> NEXT_PASS (pass_phiopt, true /* early_p */);
> + NEXT_PASS (pass_cleanup_eh);
Can you add a comment here indicating why we do this specifically before
tail recursion?
OK with that change.
Richard.
> NEXT_PASS (pass_tail_recursion);
> NEXT_PASS (pass_if_to_switch);
> NEXT_PASS (pass_convert_switch);
> - NEXT_PASS (pass_cleanup_eh);
> NEXT_PASS (pass_sccopy);
> NEXT_PASS (pass_profile);
> NEXT_PASS (pass_local_pure_const);
> --
> 2.43.0
>
