[ThinLTO] Ensure callees get hot threshold when first seen on cold path

This is split out from D27696, since it turned out to be a bug fix and
not part of the NFC efficiency change.

Keep the same adjusted (possibly decayed) threshold in both the worklist
and the ImportList. Otherwise if we encountered it first along a cold
path, the callee would be added to the worklist with a lower decayed
threshold than when it is later encountered along a hot path. But the
logic uses the threshold recorded in the ImportList entry to check if
we should re-add it, and without this patch the threshold recorded there
is the same along both paths so we don't re-add it. Using the
same possibly decayed threshold in the ImportList ensures we re-add it
later with the higher non-decayed hot path threshold.

llvm-svn: 289843

1 files changed, 28 insertions, 24 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index ce875a5ba8b..c20e59fdb94 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -316,49 +316,53 @@ static void computeImportForFunction(
     assert(ResolvedCalleeSummary->instCount() <= NewThreshold &&
            "selectCallee() didn't honor the threshold");
 
+    auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
+      // Adjust the threshold for next level of imported functions.
+      // The threshold is different for hot callsites because we can then
+      // inline chains of hot calls.
+      if (IsHotCallsite)
+        return Threshold * ImportHotInstrFactor;
+      return Threshold * ImportInstrFactor;
+    };
+
+    bool IsHotCallsite = Edge.second.Hotness == CalleeInfo::HotnessType::Hot;
+    const auto AdjThreshold = GetAdjustedThreshold(Threshold, IsHotCallsite);
+
     auto ExportModulePath = ResolvedCalleeSummary->modulePath();
     auto &ProcessedThreshold = ImportList[ExportModulePath][GUID];
     /// Since the traversal of the call graph is DFS, we can revisit a function
     /// a second time with a higher threshold. In this case, it is added back to
     /// the worklist with the new threshold.
-    if (ProcessedThreshold && ProcessedThreshold >= Threshold) {
+    if (ProcessedThreshold && ProcessedThreshold >= AdjThreshold) {
       DEBUG(dbgs() << "ignored! Target was already seen with Threshold "
                    << ProcessedThreshold << "\n");
       continue;
     }
+    bool PreviouslyImported = ProcessedThreshold != 0;
     // Mark this function as imported in this module, with the current Threshold
-    ProcessedThreshold = Threshold;
+    ProcessedThreshold = AdjThreshold;
 
     // Make exports in the source module.
     if (ExportLists) {
       auto &ExportList = (*ExportLists)[ExportModulePath];
       ExportList.insert(GUID);
-      // Mark all functions and globals referenced by this function as exported
-      // to the outside if they are defined in the same source module.
-      for (auto &Edge : ResolvedCalleeSummary->calls()) {
-        auto CalleeGUID = Edge.first.getGUID();
-        exportGlobalInModule(Index, ExportModulePath, CalleeGUID, ExportList);
-      }
-      for (auto &Ref : ResolvedCalleeSummary->refs()) {
-        auto GUID = Ref.getGUID();
-        exportGlobalInModule(Index, ExportModulePath, GUID, ExportList);
+      if (!PreviouslyImported) {
+        // This is the first time this function was exported from its source
+        // module, so mark all functions and globals it references as exported
+        // to the outside if they are defined in the same source module.
+        for (auto &Edge : ResolvedCalleeSummary->calls()) {
+          auto CalleeGUID = Edge.first.getGUID();
+          exportGlobalInModule(Index, ExportModulePath, CalleeGUID, ExportList);
+        }
+        for (auto &Ref : ResolvedCalleeSummary->refs()) {
+          auto GUID = Ref.getGUID();
+          exportGlobalInModule(Index, ExportModulePath, GUID, ExportList);
+        }
       }
     }
 
-    auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
-      // Adjust the threshold for next level of imported functions.
-      // The threshold is different for hot callsites because we can then
-      // inline chains of hot calls.
-      if (IsHotCallsite)
-        return Threshold * ImportHotInstrFactor;
-      return Threshold * ImportInstrFactor;
-    };
-
-    bool IsHotCallsite = Edge.second.Hotness == CalleeInfo::HotnessType::Hot;
-
     // Insert the newly imported function to the worklist.
-    Worklist.emplace_back(ResolvedCalleeSummary,
-                          GetAdjustedThreshold(Threshold, IsHotCallsite));
+    Worklist.emplace_back(ResolvedCalleeSummary, AdjThreshold);
   }
 }