[llvm] [LTO] Introduce a helper function summarizeImports (NFC) (PR #106179)

[Jan Voung via llvm-commits]

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@@ -1082,21 +1082,29 @@ numGlobalVarSummaries(const ModuleSummaryIndex &Index,
   return NumGVS;
 }
 
-// Given ImportMap, return the number of global variable summaries and record
-// the number of defined function summaries as output parameter.
-static unsigned
-numGlobalVarSummaries(const ModuleSummaryIndex &Index,
-                      const FunctionImporter::FunctionsToImportTy &ImportMap,
-                      unsigned &DefinedFS) {
+struct ImportSummary {
   unsigned NumGVS = 0;
-  DefinedFS = 0;
-  for (auto &[GUID, Type] : ImportMap) {
-    if (isGlobalVarSummary(Index, GUID))
-      ++NumGVS;
-    else if (Type == GlobalValueSummary::Definition)
-      ++DefinedFS;
+  unsigned DefinedFS = 0;
+  unsigned Count = 0;
+};
+
+// Compute import summary for each source module in ImportList.
+static DenseMap<StringRef, ImportSummary>
+summarizeImports(const ModuleSummaryIndex &Index,
+                 const FunctionImporter::ImportMapTy &ImportList) {
+  DenseMap<StringRef, ImportSummary> Histogram;
+
+  for (const auto &[FromModule, GUIDs] : ImportList.getImportMap()) {
+    for (const auto &[GUID, Type] : GUIDs) {
+      ImportSummary &Entry = Histogram[FromModule];
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jvoung wrote:

Can the Entry lookup be lifted to the outer loop (only depending on FromModule)?

https://github.com/llvm/llvm-project/pull/106179