Re: [RFC] RISC-V: Raise noce if-conversion cost limit

On 8/6/2026 11:53 PM, wangjue wrote:
> From: juewang <[email protected]>
>
> The branch-cost based noce limit is too small for unpredictable branches on C950 and blocks profitable Zicond sequences.  Add a per-tune factor, defaulting to one, and use five for C950.
>
> This improves 505.mcf_r by nearly 5% on C950.
>
> gcc/ChangeLog:
>
> 	* config/riscv/riscv.cc (riscv_tune_param): Add
> 	noce_ifcvt_unpredictable_cost_factor.
> 	(xt_c9501_tune_info): Set it to 5.
> 	(riscv_max_noce_ifcvt_seq_cost): Scale the branch-cost based limit.
So you can't just raise BRANCH_COST to fix this?  That's the traditional 
big hammer solution.

It might also help if you passed along a testcase.  I've found many of 
the failure to if-convert problems are due to inefficiencies in the 
sequences we generate; we can often get if-conversion to fire by 
generating better generic sequences and fixing costing goofs elsewhere.  
These tend to be more narrow fixes, but help all kinds of cases for 
RISC-V as well as other targets.

In fact, I think I fixed one of these for mcf not terribly long ago.  
  There's a reasonable chance I've looked a the underlying test already 
and have state on the problem.  If you're at all concerned about posting 
spec2017 sources in a public forum, you can pass the case directly along 
to me or even just mentioning the function may be enough.

jeff