[all-commits] [llvm/llvm-project] 801d9c: [CSSPGO] Use merged base profile for hot threshold...

[WenleiHe via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 801d9cc7b94947836ed59a506188fe9659e133dc
      https://github.com/llvm/llvm-project/commit/801d9cc7b94947836ed59a506188fe9659e133dc
  Author: Wenlei He <aktoon at gmail.com>
  Date:   2021-02-05 (Fri, 05 Feb 2021)

  Changed paths:
    M llvm/include/llvm/ProfileData/ProfileCommon.h
    M llvm/lib/ProfileData/ProfileSummaryBuilder.cpp
    M llvm/lib/ProfileData/SampleProfReader.cpp
    M llvm/lib/ProfileData/SampleProfWriter.cpp
    M llvm/test/Transforms/SampleProfile/csspgo-inline.ll
    A llvm/test/Transforms/SampleProfile/csspgo-summary.ll

  Log Message:
  -----------
  [CSSPGO] Use merged base profile for hot threshold calculation

Context-sensitive profile effectively split a function profile into many copies each representing the CFG profile of a particular calling context. That makes the count distribution looks more flat as we now have more function profiles each with lower counts, which in turn leads to lower hot thresholds. Now we tells threshold computation to merge context profile first before calculating percentile based cutoffs to compensate for seemingly flat context profile. This can be controlled by swtich `sample-profile-contextless-threshold`.

Earlier measurement showed ~0.4% perf boost with this tuning on spec2k6 for CSSPGO (with pseudo-probe and new inliner).

Differential Revision: https://reviews.llvm.org/D95980