[llvm-exegesis] parallel snippet generator: avoid Read-After-Write pitfail for instrs w/ tied variables

As it is being discussed in https://github.com/llvm/llvm-project/issues/59325,
at least for the instructions with tied variables,
when trying to parallelize the instructions,
register selection is rather bad, and may either
use a register which we have used for def,
or vice versa.

That introduces serialization, and leads to
overly pessimistic inverse throughput measurement.

The new implementation avoids that,

New result:
```
$ ninja llvm-exegesis && ./bin/llvm-exegesis --mode=inverse_throughput --opcode-name=VFMADD132PDr --max-configs-per-opcode=9182
ninja: no work to do.
Check generated assembly with: /usr/bin/objdump -d /tmp/snippet-4af034.o
---
mode:            inverse_throughput
key:
  instructions:
    - 'VFMADD132PDr XMM3 XMM3 XMM4 XMM8'
    - 'VFMADD132PDr XMM5 XMM5 XMM14 XMM7'
    - 'VFMADD132PDr XMM10 XMM10 XMM11 XMM15'
    - 'VFMADD132PDr XMM13 XMM13 XMM15 XMM15'
    - 'VFMADD132PDr XMM12 XMM12 XMM11 XMM1'
    - 'VFMADD132PDr XMM0 XMM0 XMM6 XMM9'
    - 'VFMADD132PDr XMM2 XMM2 XMM15 XMM11'
  config:          ''
  register_initial_values:
    - 'XMM3=0x0'
    - 'XMM4=0x0'
    - 'XMM8=0x0'
    - 'MXCSR=0x0'
    - 'XMM5=0x0'
    - 'XMM14=0x0'
    - 'XMM7=0x0'
    - 'XMM10=0x0'
    - 'XMM11=0x0'
    - 'XMM15=0x0'
    - 'XMM13=0x0'
    - 'XMM12=0x0'
    - 'XMM1=0x0'
    - 'XMM0=0x0'
    - 'XMM6=0x0'
    - 'XMM9=0x0'
    - 'XMM2=0x0'
cpu_name:        znver3
llvm_triple:     x86_64-unknown-linux-gnu
num_repetitions: 10000
measurements:
  - { key: inverse_throughput, value: 0.6403, per_snippet_value: 4.4821 }
error:           ''
info:            instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, randomizing registers for uses
assembled_snippet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
...
Check generated assembly with: /usr/bin/objdump -d /tmp/snippet-f05c2f.o
---
mode:            inverse_throughput
key:
  instructions:
    - 'VFMADD132PDr XMM15 XMM15 XMM11 XMM2'
    - 'VFMADD132PDr XMM5 XMM5 XMM11 XMM2'
    - 'VFMADD132PDr XMM14 XMM14 XMM11 XMM2'
    - 'VFMADD132PDr XMM4 XMM4 XMM11 XMM2'
    - 'VFMADD132PDr XMM8 XMM8 XMM11 XMM2'
    - 'VFMADD132PDr XMM3 XMM3 XMM11 XMM2'
    - 'VFMADD132PDr XMM10 XMM10 XMM11 XMM2'
    - 'VFMADD132PDr XMM7 XMM7 XMM11 XMM2'
    - 'VFMADD132PDr XMM13 XMM13 XMM11 XMM2'
    - 'VFMADD132PDr XMM9 XMM9 XMM11 XMM2'
    - 'VFMADD132PDr XMM1 XMM1 XMM11 XMM2'
    - 'VFMADD132PDr XMM6 XMM6 XMM11 XMM2'
    - 'VFMADD132PDr XMM0 XMM0 XMM11 XMM2'
    - 'VFMADD132PDr XMM12 XMM12 XMM11 XMM2'
  config:          ''
  register_initial_values:
    - 'XMM15=0x0'
    - 'XMM11=0x0'
    - 'XMM2=0x0'
    - 'MXCSR=0x0'
    - 'XMM5=0x0'
    - 'XMM14=0x0'
    - 'XMM4=0x0'
    - 'XMM8=0x0'
    - 'XMM3=0x0'
    - 'XMM10=0x0'
    - 'XMM7=0x0'
    - 'XMM13=0x0'
    - 'XMM9=0x0'
    - 'XMM1=0x0'
    - 'XMM6=0x0'
    - 'XMM0=0x0'
    - 'XMM12=0x0'
cpu_name:        znver3
llvm_triple:     x86_64-unknown-linux-gnu
num_repetitions: 10000
measurements:
  - { key: inverse_throughput, value: 0.5312, per_snippet_value: 7.4368 }
error:           ''
info:            instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, one unique register for each use position
assembled_snippet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
...
Check generated assembly with: /usr/bin/objdump -d /tmp/snippet-c32060.o
---
mode:            inverse_throughput
key:
  instructions:
    - 'VFMADD132PDr XMM10 XMM10 XMM6 XMM6'
    - 'VFMADD132PDr XMM8 XMM8 XMM6 XMM6'
    - 'VFMADD132PDr XMM12 XMM12 XMM6 XMM6'
    - 'VFMADD132PDr XMM9 XMM9 XMM6 XMM6'
    - 'VFMADD132PDr XMM7 XMM7 XMM6 XMM6'
    - 'VFMADD132PDr XMM1 XMM1 XMM6 XMM6'
    - 'VFMADD132PDr XMM0 XMM0 XMM6 XMM6'
    - 'VFMADD132PDr XMM5 XMM5 XMM6 XMM6'
    - 'VFMADD132PDr XMM11 XMM11 XMM6 XMM6'
    - 'VFMADD132PDr XMM2 XMM2 XMM6 XMM6'
    - 'VFMADD132PDr XMM15 XMM15 XMM6 XMM6'
    - 'VFMADD132PDr XMM3 XMM3 XMM6 XMM6'
    - 'VFMADD132PDr XMM14 XMM14 XMM6 XMM6'
    - 'VFMADD132PDr XMM4 XMM4 XMM6 XMM6'
    - 'VFMADD132PDr XMM13 XMM13 XMM6 XMM6'
  config:          ''
  register_initial_values:
    - 'XMM10=0x0'
    - 'XMM6=0x0'
    - 'MXCSR=0x0'
    - 'XMM8=0x0'
    - 'XMM12=0x0'
    - 'XMM9=0x0'
    - 'XMM7=0x0'
    - 'XMM1=0x0'
    - 'XMM0=0x0'
    - 'XMM5=0x0'
    - 'XMM11=0x0'
    - 'XMM2=0x0'
    - 'XMM15=0x0'
    - 'XMM3=0x0'
    - 'XMM14=0x0'
    - 'XMM4=0x0'
    - 'XMM13=0x0'
cpu_name:        znver3
llvm_triple:     x86_64-unknown-linux-gnu
num_repetitions: 10000
measurements:
  - { key: inverse_throughput, value: 0.5311, per_snippet_value: 7.9665 }
error:           ''
info:            instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, reusing the same register for all uses
assembled_snippet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
...
```

Reviewed By: courbet

Differential Revision: https://reviews.llvm.org/D139283

0 files changed, 0 insertions, 0 deletions