Re: xthead regression with [COMMITTED] RISC-V: const: hide mvconst splitter from IRA

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/9/23 14:36, Vineet Gupta wrote:
> Hi Christoph,
> 
> On 10/9/23 12:06, Patrick O'Neill wrote:
>>
>> Hi Vineet,
>>
>> We're seeing a regression on all riscv targets after this patch:|
>>
>> FAIL: gcc.target/riscv/xtheadcondmov-indirect.c -O2 
>> check-function-bodies ConNmv_imm_imm_reg||
>> FAIL: gcc.target/riscv/xtheadcondmov-indirect.c -O3 -g 
>> check-function-bodies ConNmv_imm_imm_reg
>>
>> Debug log output:
>> body: \taddi    a[0-9]+,a[0-9]+,-1000+
>> \tli    a[0-9]+,9998336+
>> \taddi    a[0-9]+,a[0-9]+,1664+
>> \tth.mveqz    a[0-9]+,a[0-9]+,a[0-9]+
>> \tret
>>
>> against:     li    a5,9998336
>>     addi    a4,a0,-1000
>>     addi    a0,a5,1664
>>     th.mveqz    a0,a1,a4
>>     ret|
>>
>> https://github.com/patrick-rivos/gcc-postcommit-ci/issues/8
>> https://github.com/ewlu/riscv-gnu-toolchain/issues/286
>>
> 
> It seems with my patch, exactly same instructions get out of order (for 
> -O2/-O3) tripping up the test results and differ from say O1 for exact 
> same build.
> 
> -O2 w/ patch
> ConNmv_imm_imm_reg:
>      li    a5,9998336
>      addi    a4,a0,-1000
>      addi    a0,a5,1664
>      th.mveqz    a0,a1,a4
>      ret
> 
> -O1 w/ patch
> ConNmv_imm_imm_reg:
>      addi    a4,a0,-1000
>      li    a5,9998336
>      addi    a0,a5,1664
>      th.mveqz    a0,a1,a4
>      ret
> 
> I'm not sure if there is an easy way to handle that.
> Is there a real reason for testing the full sequences verbatim, or is 
> testing number of occurrences of th.mv{eqz,nez} enough.
> It seems Jeff recently added -fno-sched-pressure to avoid similar issues 
> but that apparently is no longer sufficient.
I'd suggest doing a count test rather than an exact match.

Verify you get a single li, two addis and one th.mveqz

Jeff