Ok I see your idea and we need to adjust scalar_to_vec accurately. Inside the
loop we have these 2 scalar_to_vec:
1. MIN_EXPR <patt_28, 15> 1 times scalar_to_vec costs 1 in prologue
This scalar_to_vec cost should be 0 or 1 since it only generate single
instructions: vmv.v.i v16,15
2. 32872 >> patt_26 1 times scalar_to_vec costs 1 in prologue
This cost should be higher since it cost 3 instructions:
li a4,-32768
addiw a4,a4,104
vmv.v.x v16,a4
Am I correct ?
I guess if we cost 1 case as 1 cost and 2 case as 3 cost. Then we will be good.
juzhe.zh...@rivai.ai
From: Robin Dapp
Date: 2024-01-11 18:14
To: juzhe.zh...@rivai.ai; Richard Biener
CC: rdapp.gcc; gcc-patches; kito.cheng; Kito.cheng; jeffreyalaw
Subject: Re: [PATCH] RISC-V: Increase scalar_to_vec_cost from 1 to 3
> Yeah... I just noticed. I should set it as 4 to fix it with biggest VLEN
> size,
> that is, -march=rv64gcv_zvl4096b --param=riscv-autovec-lmul=m8...
>
> I am confused now how to fix this case.
4 is definitely too high compared to a regular instruction.
vmv.vx could even be zero-cost for constants.
To catch constants we could add handling in add_stmt_cost, inspecting
the stmt directly.
Regards
Robin
