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

[via llvm-commits]

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@@ -222,6 +260,57 @@ 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");
+
+  AnchorList FilteredProfileAnchorList;
+  for (const auto &I : ProfileAnchors)
+    FilteredProfileAnchorList.emplace_back(I);
+
+  AnchorList FilteredIRAnchorsList;
+  // Filter the non-callsite from IRAnchors.
+  for (const auto &I : IRAnchors) {
+    if (I.second.stringRef().empty())
+      continue;
+    FilteredIRAnchorsList.emplace_back(I);
+  }
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WenleiHe wrote:

Ah ok. can you remind me why we need non-call site to be in the anchor map? I thought we only consider call sites as anchors.

What I'm really trying get at is whether it's possible to make AnchorMap and AnchorList really close, and maybe even merge them. Maybe it's not impossible, but wanted to understand all the reasons. 

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