[PGO] Enable the working set size scaling under the partial sample PGO.

[hjyamauchi]

Summary

Following up D79831.

[davidxl]

lgtm

[MaskRay]

arc adds many unneeded tags from Phabricator. You can drop Reviewers: Subscribers: Tags: and the text Summary: with the following script:

arcfilter () {
  arc amend
  git log -1 --pretty=%B | awk '/Reviewers:|Subscribers:/{p=1} /Reviewed By:|Differential Revision:/{p=0} !p && !/^Summary:$/ {sub(/^Summary: /,"");print}' | git commit --amend --date=now -F -
}

Reviewed By: is considered important by some people (https://lists.llvm.org/pipermail/llvm-dev/2020-January/137889.html). You should keep the tag. (I started to use --date=now because some people find author date != committer date annoying. The committer date is usually what people care.))

llvm/lib/Analysis/ProfileSummaryInfo.cpp

static cl::opt<int> ProfileSummaryColdCount(
     cl::desc("A fixed cold count that overrides the count derived from"
              " profile-summary-cutoff-cold"));
 
 static cl::opt<bool> PartialProfile(
     "partial-profile", cl::Hidden, cl::init(false),
     cl::desc("Specify the current profile is used as a partial profile."));
 
 cl::opt<bool> ScalePartialSampleProfileWorkingSetSize(
-    "scale-partial-sample-profile-working-set-size", cl::Hidden,
-    cl::init(false),
+    "scale-partial-sample-profile-working-set-size", cl::Hidden, cl::init(true),
     cl::desc(
         "If true, scale the working set size of the partial sample profile "
         "by the partial profile ratio to reflect the size of the program "
         "being compiled."));
 
 static cl::opt<double> PartialSampleProfileWorkingSetSizeScaleFactor(
     "partial-sample-profile-working-set-size-scale-factor", cl::Hidden,
     cl::init(0.008),