[ThinLTO] only emit used or referenced CFI records to index

Summary: We emit CFI_FUNCTION_DEFS and CFI_FUNCTION_DECLS to
distributed ThinLTO indices to implement indirect function call
checking.  This change causes us to only emit entries for functions
that are either defined or used by the module we're writing the index
for (instead of all functions in the combined index), which can make
the indices substantially smaller.

Fixes PR42378.

Reviewers: pcc, vitalybuka, eugenis

Subscribers: mehdi_amini, hiraditya, dexonsmith, arphaman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63887

llvm-svn: 365537

1 files changed, 22 insertions, 8 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 65b9e0b..33e28c0 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -3973,9 +3973,13 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     NameVals.clear();
   };
 
+  std::set<GlobalValue::GUID> DefOrUseGUIDs;
   forEachSummary([&](GVInfo I, bool IsAliasee) {
     GlobalValueSummary *S = I.second;
     assert(S);
+    DefOrUseGUIDs.insert(I.first);
+    for (const ValueInfo &VI : S->refs())
+      DefOrUseGUIDs.insert(VI.getGUID());
 
     auto ValueId = getValueId(I.first);
     assert(ValueId);
@@ -4120,20 +4124,30 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
 
   if (!Index.cfiFunctionDefs().empty()) {
     for (auto &S : Index.cfiFunctionDefs()) {
-      NameVals.push_back(StrtabBuilder.add(S));
-      NameVals.push_back(S.size());
+      if (DefOrUseGUIDs.count(
+              GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(S)))) {
+        NameVals.push_back(StrtabBuilder.add(S));
+        NameVals.push_back(S.size());
+      }
+    }
+    if (!NameVals.empty()) {
+      Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DEFS, NameVals);
+      NameVals.clear();
     }
-    Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DEFS, NameVals);
-    NameVals.clear();
   }
 
   if (!Index.cfiFunctionDecls().empty()) {
     for (auto &S : Index.cfiFunctionDecls()) {
-      NameVals.push_back(StrtabBuilder.add(S));
-      NameVals.push_back(S.size());
+      if (DefOrUseGUIDs.count(
+              GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(S)))) {
+        NameVals.push_back(StrtabBuilder.add(S));
+        NameVals.push_back(S.size());
+      }
+    }
+    if (!NameVals.empty()) {
+      Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DECLS, NameVals);
+      NameVals.clear();
     }
-    Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DECLS, NameVals);
-    NameVals.clear();
   }
 
   // Walk the GUIDs that were referenced, and write the