[llvm] [ctx_prof] Extend `WorkloadImportsManager` to use the contextual profile (PR #98682)

[Teresa Johnson via llvm-commits]

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@@ -672,14 +670,78 @@ class WorkloadImportsManager : public ModuleImportsManager {
       });
     }
   }
+
+  void loadFromCtxProf() {
+    std::error_code EC;
+    auto BufferOrErr = MemoryBuffer::getFileOrSTDIN(ContextualProfile);
+    if (std::error_code EC = BufferOrErr.getError()) {
+      report_fatal_error("Failed to open contextual profile file");
+      return;
+    }
+    auto Buffer = std::move(BufferOrErr.get());
+
+    BitstreamCursor Cursor(*Buffer);
+    PGOCtxProfileReader Reader(Cursor);
+    auto Ctx = Reader.loadContexts();
+    if (!Ctx) {
+      report_fatal_error("Failed to parse contextual profiles");
+      return;
+    }
+    const auto &CtxMap = *Ctx;
+    DenseSet<GlobalValue::GUID> ContainedGUIDs;
+    for (const auto &[RootGuid, Root] : CtxMap) {
+      // Avoid ContainedGUIDs to get in/out of scope. Reuse its memory for
+      // subsequent roots, but clear its contents.
+      ContainedGUIDs.clear();
+
+      auto RootVI = Index.getValueInfo(RootGuid);
+      if (!RootVI) {
+        LLVM_DEBUG(dbgs() << "[Workload] Root " << RootGuid
+                          << " not found in this linkage unit.\n");
+        continue;
+      }
+      if (RootVI.getSummaryList().size() != 1) {
+        LLVM_DEBUG(dbgs() << "[Workload] Root " << RootGuid
+                          << " should have exactly one summary, but has "
+                          << RootVI.getSummaryList().size() << ". Skipping.\n");
+        continue;
+      }
+      StringRef RootDefiningModule =
+          RootVI.getSummaryList().front()->modulePath();
+      LLVM_DEBUG(dbgs() << "[Workload] Root defining module for " << RootGuid
+                        << " is : " << RootDefiningModule << "\n");
+      auto &Set = Workloads[RootDefiningModule];
+      Root.getContainedGuids(ContainedGUIDs);
+      for (auto Guid : ContainedGUIDs)
+        if (auto VI = Index.getValueInfo(Guid))
+          Set.insert(VI);
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teresajohnson wrote:

The json case has some debug printing of the eventual Set contents - needed here too?

https://github.com/llvm/llvm-project/pull/98682