[PATCH] D97396: Use the default seed value for djb hash for StringMap

Wed Feb 24 12:59:53 PST 2021

serge-sans-paille added a comment.

In D97396#2585265 <https://reviews.llvm.org/D97396#2585265>, @JDevlieghere wrote:

>> The performance gain was worth doing the test update.
>
> How did you measure this and what were the results?

I ran the following before / after the patch:

  curl -L -O https://github.com/azadkuh/sqlite-amalgamation/raw/master/sqlite3.c
  perf stat -e instructions clang -O0 -c sqlite3.c -o/dev/null -w

And compared the instruction count reported. This is similar to the approach taken by http://llvm-compile-time-tracker.com/ and confirms the literature about the default seed for that hashing function.

Before the patch: 6,139,868,068 instructions
After the patch:    6,137,774,225 instructions

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97396/new/

https://reviews.llvm.org/D97396