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llvm / llvm-project / 00fabd21bce85259a74a64a435874d290ed2da38
commit00fabd21bce85259a74a64a435874d290ed2da38[log] [tgz]
authorMichael Maitland <michaeltmaitland@gmail.com>Thu Mar 20 15:20:04 2025 -0400
committerGitHub <noreply@github.com>Thu Mar 20 15:20:04 2025 -0400
treec79f4f4af2bc55fae87177b8f292f34cb68fb641
parent221b0117fd21d45098ead779a040a4b939a5c84f [diff]
[RISCV][RegAlloc] Add getCSRFirstUseCost for RISC-V (#131349)

This is based off of 63efd8e7e68bc.

The following table shows the percent change to the dynamic instruction
count when the function in this patch returns 0 (default) versus other
values.

| benchmark | % speedup 1 over 0 | % speedup 4 over 0 | % speedup 16
over 0 | % speedup 64 over 0 | % speedup 128 over 0 |
| --------------- | ---------------------- | --------------------- |
--------------------- | -------------------- | -------------------- |
| 500.perlbench_r | 0.001018570165 | 0.001049508358 | 0.001001106529 |
0.03382582818 | 0.03395354577 |
| 502.gcc_r | 0.02850551412 | 0.02170512371 | 0.01453021263 |
0.06011008637 | 0.1215691521 |
| 505.mcf_r | -0.00009506373338 | -0.00009090057642 | -0.0000860991497 |
-0.00005027849766 | 0.00001251173791 |
| 520.omnetpp_r | 0.2958940288 | 0.2959715925 | 0.2961141505 |
0.2959823497 | 0.2963124341 |
| 523.xalancbmk_r | -0.0327074721 | -0.01037021046 | -0.3226810542 |
0.02127133714 | 0.02765388389 |
| 525.x264_r | 0.0000001381714403 | -0.00000007041540345 |
-0.00000002156399465 | 0.0000002108993364 | 0.0000002463382874 |
| 531.deepsjeng_r | 0.00000000339777238 | 0.000000003874652714 |
0.000000003636212547 | 0.000000003874652714 | 0.000000003159332213 |
| 541.leela_r | 0.0009186059953 | -0.000424159199 | 0.0004984456879 |
0.274948447 | 0.8135521414 |
| 557.xz_r | -0.000000003547118854 | -0.00004896449559 |
-0.00004910691576 | -0.0000491109983 | -0.00004895599589 |
| geomean | 0.03265937388 | 0.03424232324 | -0.00107917442 |
0.07629116165 | 0.1439913192 |

The following table shows the percent change to the runtime when the
function in this patch returns 0 (default) versus other values.

| benchmark | % speedup 1 over 0 | % speedup 4 over 0 | % speedup 16
over 0 | % speedup 64 over 0 | %speedup 128 over 0 |
| --------------- | ------------------ | ------------------ |
------------------- | ------------------- | ------------------- |
| 500.perlbench_r | 0.1722356761 | 0.2269681109 | 0.2596825578 |
0.361573851 | 1.15041305 |
| 502.gcc_r | -0.548415855 | -0.06187002799 | -0.5553684674 |
-0.8876686237 | -0.4668665535 |
| 505.mcf_r | -0.8786414258 | -0.4150938441 | -1.035517726 |
-0.1860770377 | -0.01904825648 |
| 520.omnetpp_r | 0.4130256072 | 0.6595976188 | 0.897332171 |
0.6252625622 | 0.3869467278 |
| 523.xalancbmk_r | 1.318132014 | -0.003927574 | 1.025962975 |
1.090320253 | -0.789206202 |
| 525.x264_r | -0.03112871796 | -0.00167557587 | 0.06932423155 |
-0.1919840015 | -0.1203585732 |
| 531.deepsjeng_r | -0.259516072 | -0.01973455652 | -0.2723227894 |
-0.005417022257 | -0.02222388177 |
| 541.leela_r | -0.3497178495 | -0.3510447393 | 0.1274508001 |
0.6485542452 | 0.2880651727 |
| 557.xz_r | 0.7683565263 | -0.2197509447 | -0.0431183874 |
0.07518130872 | 0.5236853039 |
| geomean | 0.06506952742 | -0.0211865386 | 0.05072694648 | 0.1684530637
| 0.1020533557 |

I chose to set the value to 5 on RISC-V because it has improvement to
both the dynamic IC and the runtime and because it showed good results
empirically and had a similar effect as setting it to higher numbers.

I looked at some diff and it seems like this patch leads to two things:
1. Less spilling -- not spilling the CSR led to better register
allocation and helped us avoid spills down the line
2. Avoid spilling CSR but spill more on paths that static heuristics
estimate as cold.
3 files changed
tree: c79f4f4af2bc55fae87177b8f292f34cb68fb641
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. pstl/
  25. runtimes/
  26. third-party/
  27. utils/
  28. .clang-format
  29. .clang-tidy
  30. .git-blame-ignore-revs
  31. .gitattributes
  32. .gitignore
  33. .mailmap
  34. CODE_OF_CONDUCT.md
  35. CONTRIBUTING.md
  36. LICENSE.TXT
  37. pyproject.toml
  38. README.md
  39. SECURITY.md
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