[PATCH] D112333: [DebugInfo][InstrRef][NFC] Use DenseMaps where we can, use more efficient ValueIDNum repr

Mon Oct 25 05:53:36 PDT 2021

jmorse added inline comments.

================
Comment at: llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h:1029
+  static unsigned getHashValue(const ValueIDNum &Val) {
+    return Val.asU64();
+  }
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Orlando wrote:
> Curious if you have you tried experimenting with this hash function at all?
I tried the standard llvm hash_code, which caused CTMark to be slower. Looking at the assembly, hash_code adds three or four instructions, and that's all. This difference is for the transition of hash_code to nothing, and shows a speedup:

  http://llvm-compile-time-tracker.com/compare.php?from=d6553eab88c71e1d797163295750f2d1bc3d86ba&to=cfe24102d48687ccb7fbcc8311488bb3a87010bb&stat=instructions

IMO, the distribution is (seemingly) good enough already.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D112333/new/

https://reviews.llvm.org/D112333