Re: [PATCH] RISC-V: Enable pressure-aware scheduling by default.

[Vineet Gupta <vineetg@rivosinc.com>]

On 8/18/23 16:08, Jeff Law wrote:
>> There is some slight regression in code quality for a number of
>> vector tests where we spill more due to different instructions order.
>> The ones I looked at were a mix of bad luck and/or brittle tests.
>> Comparing the size of the generated assembly or the number of vsetvls
>> for SPECint also didn't show any immediate benefit but that's obviously
>> not a very fine-grained analysis.
> Yea.  In fact I wouldn't really expect significant changes other than 
> those key loops in x264.

Care to elaborate a bit more please. I've seen severe reg pressure / 
spills in a bunch of others: cactu, lbm, exchange2. Is there something 
specific to x264 spills ?

>
>>
>> diff --git a/gcc/common/config/riscv/riscv-common.cc 
>> b/gcc/common/config/riscv/riscv-common.cc
>> index 4737dcd44a1..59848b21162 100644
>> --- a/gcc/common/config/riscv/riscv-common.cc
>> +++ b/gcc/common/config/riscv/riscv-common.cc
>> @@ -2017,9 +2017,11 @@ static const struct default_options 
>> riscv_option_optimization_table[] =
>>     {
>>       { OPT_LEVELS_1_PLUS, OPT_fsection_anchors, NULL, 1 },
>>       { OPT_LEVELS_2_PLUS, OPT_free, NULL, 1 },
>> +    { OPT_LEVELS_1_PLUS, OPT_fsched_pressure, NULL, 1 },

Nit2: maybe move this 1 line up to keep LEVEL_1 together, at least the 
new ones being added.

>>   #if TARGET_DEFAULT_ASYNC_UNWIND_TABLES == 1
>>       { OPT_LEVELS_ALL, OPT_fasynchronous_unwind_tables, NULL, 1 },
>>       { OPT_LEVELS_ALL, OPT_funwind_tables, NULL, 1},
>> +    /* Enable -fsched-pressure by default when optimizing.  */
>>   #endif
>>       { OPT_LEVELS_NONE, 0, NULL, 0 }
>>     };
> Shouldn't the comment move up to before the OPT_fsched_pressure line?

Yep I had the exact same first though but then thought it was something 
deeper.
Turned out to be Occam's Razor after all :-)

Thx,
-Vineet