[StaleProfileMatching] Use only profile anchor size for similarity calculation (#126783)

We observed that the number of IR anchors is usually greater than the
number of profile anchors, because IR anchors can be optimized away
later and llvm-profgen might not generate profiles for cold callsites.
This can cause missing function matches. I’m changing the similarity
calculation to use only the profile anchor size. In another point of
view, It also makes sense to reuse as many profile anchors as possible
regardless of the new functions in the IR.

Author: wlei-llvm

llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp

@@ -790,9 +790,8 @@ bool SampleProfileMatcher::functionMatchesProfileHelper(
       longestCommonSequence(FilteredIRAnchorsList, FilteredProfileAnchorList,
                             false /* Match unused functions */);
 
-  Similarity =
-      static_cast<float>(MatchedAnchors.size()) * 2 /
-      (FilteredIRAnchorsList.size() + FilteredProfileAnchorList.size());
+  Similarity = static_cast<float>(MatchedAnchors.size()) /
+               FilteredProfileAnchorList.size();
 
   LLVM_DEBUG(dbgs() << "The similarity between " << IRFunc.getName()
                     << "(IR) and " << ProfFunc << "(profile) is "

llvm/test/Transforms/SampleProfile/pseudo-probe-stale-profile-renaming.ll

@@ -1,14 +1,14 @@
 ; REQUIRES: x86_64-linux
 ; REQUIRES: asserts
-; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-renaming.prof --salvage-stale-profile --salvage-unused-profile -report-profile-staleness -persist-profile-staleness -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl -pass-remarks=inline --min-call-count-for-cg-matching=0 --min-func-count-for-cg-matching=0 2>&1 | FileCheck %s
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-renaming.prof --salvage-stale-profile --salvage-unused-profile -report-profile-staleness -persist-profile-staleness -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl -pass-remarks=inline --min-call-count-for-cg-matching=0 --min-func-count-for-cg-matching=0 --func-profile-similarity-threshold=70 2>&1 | FileCheck %s
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-renaming.prof --salvage-stale-profile --salvage-unused-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl --min-call-count-for-cg-matching=10 --min-func-count-for-cg-matching=10 2>&1 | FileCheck %s  --check-prefix=TINY-FUNC
 
 ; Verify find new IR functions.
 ; CHECK: Function new_block_only is not in profile or profile symbol list.
 ; CHECK: Function new_foo is not in profile or profile symbol list.
 
 ; CHECK: Run stale profile matching for main
-; CHECK: The similarity between new_foo(IR) and foo(profile) is 0.86
+; CHECK: The similarity between new_foo(IR) and foo(profile) is 0.75
 ; CHECK: Function:new_foo matches profile:foo
 ; CHECK: Run stale profile matching for cold_func
 ; CHECK: The checksums for new_block_only(IR) and block_only(Profile) match.