[WholeProgramDevirt] Add check for AvailableExternal and give up icall.branch.funnel

llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp

@@ -1456,6 +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

@@ -0,0 +1,56 @@
+; RUN: opt -S -passes=wholeprogramdevirt -whole-program-visibility %s | FileCheck %s
+
+; This test is reduced from C++ code like this:
+; class A :public std::exception {
+; public:
+;   A() {};
+;   const char* what () const throw () {return "A";}
+; };
+; long test(std::exception *p) {
+;   const char* ch = p->what();
+;   ...;
+; }
+;
+; 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.
+; 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"
+
+@_ZTVSt9exception = available_externally constant { [5 x ptr] } { [5 x ptr] [ptr null, ptr null, ptr null, ptr null, ptr @_ZNKSt9exception4whatEv] }, !type !0, !type !1
+@_ZTV1A.0 = constant [5 x ptr] [ptr null, ptr null, ptr null, ptr null, ptr @_ZNK1A4whatEv], !type !3, !type !4, !type !5, !type !6
+
+declare ptr @_ZNKSt9exception4whatEv()
+
+define ptr @_Z4testPSt9exception() {
+  %1 = load ptr, ptr null, align 8
+  %2 = call i1 @llvm.type.test(ptr %1, metadata !"_ZTSSt9exception")
+  tail call void @llvm.assume(i1 %2)
+  %3 = getelementptr i8, ptr %1, i64 16
+  %4 = load ptr, ptr %3, align 8
+  %5 = tail call ptr %4(ptr null)
+  ret ptr %5
+}
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write)
+declare void @llvm.assume(i1 noundef) #0
+
+declare ptr @_ZNK1A4whatEv()
+
+; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
+declare i1 @llvm.type.test(ptr, metadata) #1
+
+; CHECK-NOT: call void (...) @llvm.icall.branch.funnel
+
+attributes #0 = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) }
+attributes #1 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
+
+!0 = !{i64 16, !"_ZTSSt9exception"}
+!1 = !{i64 32, !"_ZTSMSt9exceptionKDoFPKcvE.virtual"}
+!3 = !{i32 16, !"_ZTS1A"}
+!4 = !{i32 32, !"_ZTSM1AKDoFPKcvE.virtual"}
+!5 = !{i32 16, !"_ZTSSt9exception"}
+!6 = !{i32 32, !"_ZTSMSt9exceptionKDoFPKcvE.virtual"}