[llvm] [SampleFDO] Improve stale profile matching by diff algorithm (PR #87375)

[via llvm-commits]

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@@ -222,6 +290,58 @@ void SampleProfileMatcher::runStaleProfileMatching(
   }
 }
 
+// Call target name anchor based profile fuzzy matching.
+// Input:
+// For IR locations, the anchor is the callee name of direct callsite; For
+// profile locations, it's the call target name for BodySamples or inlinee's
+// profile name for CallsiteSamples.
+// Matching heuristic:
+// First match all the anchors using the diff algorithm, then split the
+// non-anchor locations between the two anchors evenly, first half are matched
+// based on the start anchor, second half are matched based on the end anchor.
+// For example, given:
+// IR locations:      [1, 2(foo), 3, 5, 6(bar), 7]
+// Profile locations: [1, 2, 3(foo), 4, 7, 8(bar), 9]
+// The matching gives:
+//   [1,    2(foo), 3,  5,  6(bar), 7]
+//    |     |       |   |     |     |
+//   [1, 2, 3(foo), 4,  7,  8(bar), 9]
+// The output mapping: [2->3, 3->4, 5->7, 6->8, 7->9].
+void SampleProfileMatcher::runStaleProfileMatching(
+    const Function &F, const AnchorMap &IRAnchors,
+    const AnchorMap &ProfileAnchors, LocToLocMap &IRToProfileLocationMap) {
+  LLVM_DEBUG(dbgs() << "Run stale profile matching for " << F.getName()
+                    << "\n");
+  assert(IRToProfileLocationMap.empty() &&
+         "Run stale profile matching only once per function");
+
+  std::vector<Anchor> ProfileCallsiteAnchors;
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WenleiHe wrote:

By definition, anchors are call sites. The key difference between `ProfileCallsiteAnchors` and `ProfileAnchors` is not callsites, but sequence vs map, plus filtering?

 How about 
ProfileCallsiteAnchors -> FilteredProfileAnchorList
IRAnchors -> FilteredIRAnchorsList

https://github.com/llvm/llvm-project/pull/87375