Postpone check in tryICallBranchFunnel and tighten condition to any AE.

Author: tianleliu

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -1093,7 +1093,6 @@ bool DevirtModule::tryFindVirtualCallTargets(
     std::vector<VirtualCallTarget> &TargetsForSlot,
     const std::set<TypeMemberInfo> &TypeMemberInfos, uint64_t ByteOffset,
     ModuleSummaryIndex *ExportSummary) {
-  bool HasAvailableExternally = false;
   for (const TypeMemberInfo &TM : TypeMemberInfos) {
     if (!TM.Bits->GV->isConstant())
       return false;
@@ -1104,16 +1103,6 @@ bool DevirtModule::tryFindVirtualCallTargets(
         GlobalObject::VCallVisibilityPublic)
       return false;
 
-    // Record if the first GV is AvailableExternally
-    if (TargetsForSlot.empty())
-      HasAvailableExternally = TM.Bits->GV->hasAvailableExternallyLinkage();
-
-    // When the first GV is AvailableExternally, check if all other GVs are
-    // also AvailableExternally. If they are not the same, return false.
-    if (!TargetsForSlot.empty() && HasAvailableExternally &&
-        !TM.Bits->GV->hasAvailableExternallyLinkage())
-      return false;
-
     Function *Fn = nullptr;
     Constant *C = nullptr;
     std::tie(Fn, C) =
@@ -1467,6 +1456,12 @@ void DevirtModule::tryICallBranchFunnel(
   if (!HasNonDevirt)
     return;
 
+  // If any GV is AvailableExternally, drop to generate branch.funnel
+  for (auto &T : TargetsForSlot) {
+    if (T.TM->Bits->GV->hasAvailableExternallyLinkage())
+      return;
+  }
+
   FunctionType *FT =
       FunctionType::get(Type::getVoidTy(M.getContext()), {Int8PtrTy}, true);
   Function *JT;

llvm/test/Transforms/WholeProgramDevirt/availableexternal-check.ll

@@ -11,12 +11,11 @@
 ;   ...;
 ; }
 ;
-; Build command is "clang++ -O2 -target x86_64-unknown-linux -flto=thin \
+; Build command is "clang++ -O2 -target x86_64-unknown-linux -flto=full \
 ; -fwhole-program-vtables -static-libstdc++  -Wl,-plugin-opt=-whole-program-visibility"
 ;
 ; _ZTVSt9exception's visibility is 1 (Linkage Unit), and available_externally.
-; But another vtable _ZTV1A.0 is not available_externally.
-; They should not do devirtualization because they are in different linkage type.
+; If any GV is available_externally, icall.branch.funnel should not be generated.
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux"