================
@@ -911,6 +916,63 @@ static void setLiveRoot(ModuleSummaryIndex &Index,
StringRef Name) {
Summary->setLive(true);
}
+// Return true if the User U is reachable from a non-vtable user
+// through the use-def chain.
+static bool hasNonVTableUsers(const User *U, CXXABI *ABI) {
+ LLVM_DEBUG(dbgs() << "Check if " << *U << "has vtable users\n");
+ if (isa<Instruction>(U)) {
+ // If the type info is used in dynamic_cast or exception handling,
+ // its user must be the instruction.
+ return true;
+ }
+
+ // The virtual table type is either a struct of arrays. For example:
+ // @vtable = constant { [3 x ptr] } { [3 x ptr] [ ptr null, ptr @rtti, ptr
@vf] }
+ //
+ // In this case, the user of @rtti is an anonymous ConstantArray.
+ // Therefore, if the user of the type information is anonymous,
+ // we need to perform a depth-first search (DFS) to locate its named users.
+ //
+ // And we also need to iterate its users if the current user is the type
+ // info global variable itself.
+ StringRef Name = U->getName();
+ if (Name.empty() || ABI->isTypeInfo(Name)) {
+ for (const User *It : U->users())
+ if (hasNonVTableUsers(It, ABI))
+ return true;
+ return false;
+ }
+
+ if (!ABI->isVTable(Name))
+ return true;
+
+ return false;
+}
+
+static void analyzeRTTIVars(ModuleSummaryIndex &Index, const Module &M) {
+ Triple TT(M.getTargetTriple());
+
+ std::unique_ptr<CXXABI> ABI = CXXABI::Create(TT);
+ if (!ABI)
+ return;
+
+ for (const GlobalVariable &GV : M.globals()) {
+ if (!ABI->isTypeInfo(GV.getName()))
+ continue;
+
+ if (hasNonVTableUsers(&GV, ABI.get())) {
+ std::string TypeName =
+ ABI->getTypeNameFromTypeInfo(GV.getName());
----------------
teresajohnson wrote:
In WPD we simply hardcode these prefixes - the assumption is if the name starts
with one prefix, we can assume what the other is. See
https://github.com/llvm/llvm-project/blob/c6654806949f0498fdd2d009b66e62041c21de36/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp#L831-L839.
If we can avoid adding all the CXXABI handling to LLVM and the TargetTriple/OS
checks to LTO that would be ideal
https://github.com/llvm/llvm-project/pull/126336
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