[llvm] [MemProf] Add basic summary section support (PR #141805)

[Kazu Hirata via llvm-commits]

================
@@ -3312,6 +3313,19 @@ static int showMemProfProfile(ShowFormat SFormat, raw_fd_ostream &OS) {
 
   auto Reader = std::move(ReaderOrErr.get());
   memprof::AllMemProfData Data = Reader->getAllMemProfData();
+
+  // For v4 and above the summary is serialized in the indexed profile, and can
+  // be accessed from the reader. Earlier versions build the summary below.
+  // The summary is emitted as YAML comments at the start of the output.
+  auto *MemProfSum = Reader->getMemProfSummary();
+  if (MemProfSum) {
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kazutakahirata wrote:

nit: Combine like so:

```suggestion
  if (auto *MemProfSum = Reader->getMemProfSummary()) {
```

https://github.com/llvm/llvm-project/pull/141805