Re: [PATCH 2/3] LoongArch: Fix instruction costs [PR112936]

[chenglulu <chenglulu@loongson.cn>]

在 2023/12/13 下午9:20, Xi Ruoyao 写道:
> On Wed, 2023-12-13 at 20:22 +0800, chenglulu wrote:
>
> 在 2023/12/10 上午1:03, Xi Ruoyao 写道:
> Replace the instruction costs in loongarch_rtx_cost_data constructor
> based on micro-benchmark results on LA464 and LA664.
>
> This allows optimizations like "x * 17" to alsl, and "x * 68" to alsl
> and slli.
>
> gcc/ChangeLog:
>
>   	PR target/112936
>   	* config/loongarch/loongarch-def.cc
>   	(loongarch_rtx_cost_data::loongarch_rtx_cost_data): Update
>   	instruction costs per micro-benchmark results.
>   	(loongarch_rtx_cost_optimize_size): Set all instruction costs
>   	to (COSTS_N_INSNS (1) + 1).
>   	* config/loongarch/loongarch.cc (loongarch_rtx_costs): Remove
>   	special case for multiplication when optimizing for size.
>   	Adjust division cost when TARGET_64BIT && !TARGET_DIV32.
>   	Account the extra cost when TARGET_CHECK_ZERO_DIV and
>   	optimizing for speed.
>
> gcc/testsuite/ChangeLog
>
>   	PR target/112936
>   	* gcc.target/loongarch/mul-const-reduction.c: New test.
> ---
>     gcc/config/loongarch/loongarch-def.cc         | 39 ++++++++++---------
>     gcc/config/loongarch/loongarch.cc             | 22 +++++------
>     .../loongarch/mul-const-reduction.c           | 11 ++++++
>     3 files changed, 43 insertions(+), 29 deletions(-)
>     create mode 100644 gcc/testsuite/gcc.target/loongarch/mul-const-reduction.c
>
> Well, I'm curious about how the value of this cost is obtained.
>
> I just make a loop containing 1000 mul.w instructions, then run the loop
> 1000000 times and compare the time usage with running another loop
> containing 1000 addi.w instructions iterated 1000000 times too.
> Likewise for other instructions...
>
Ok. I need to do a performance comparison of the spec here. Probably 
tomorrow the results will be available.

Thanks!