[WPD] Use new llvm.public.type.test intrinsic for potentially publicly visible classes

Turning on opaque pointers has uncovered an issue with WPD where we currently pattern match away `assume(type.test)` in WPD so that a later LTT doesn't resolve the type test to undef and introduce an `assume(false)`. The pattern matching can fail in cases where we transform two `assume(type.test)`s into `assume(phi(type.test.1, type.test.2))`.

Currently we create `assume(type.test)` for all virtual calls that might be devirtualized. This is to support `-Wl,--lto-whole-program-visibility`.

To prevent this, all virtual calls that may not be in the same LTO module instead use a new `llvm.public.type.test` intrinsic in place of the `llvm.type.test`. Then when we know if `-Wl,--lto-whole-program-visibility` is passed or not, we can either replace all `llvm.public.type.test` with `llvm.type.test`, or replace all `llvm.public.type.test` with `true`. This prevents WPD from trying to pattern match away `assume(type.test)` for public virtual calls when failing the pattern matching will result in miscompiles.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D128955

1 files changed, 10 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index cde3171..c6696c4 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2698,15 +2698,21 @@ void CodeGenFunction::EmitTypeMetadataCodeForVCall(const CXXRecordDecl *RD,
            // Don't insert type test assumes if we are forcing public
            // visibility.
            !CGM.AlwaysHasLTOVisibilityPublic(RD)) {
-    llvm::Metadata *MD =
-        CGM.CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
+    QualType Ty = QualType(RD->getTypeForDecl(), 0);
+    llvm::Metadata *MD = CGM.CreateMetadataIdentifierForType(Ty);
     llvm::Value *TypeId =
         llvm::MetadataAsValue::get(CGM.getLLVMContext(), MD);
 
     llvm::Value *CastedVTable = Builder.CreateBitCast(VTable, Int8PtrTy);
+    // If we already know that the call has hidden LTO visibility, emit
+    // @llvm.type.test(). Otherwise emit @llvm.public.type.test(), which WPD
+    // will convert to @llvm.type.test() if we assert at link time that we have
+    // whole program visibility.
+    llvm::Intrinsic::ID IID = CGM.HasHiddenLTOVisibility(RD)
+                                  ? llvm::Intrinsic::type_test
+                                  : llvm::Intrinsic::public_type_test;
     llvm::Value *TypeTest =
-        Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::type_test),
-                           {CastedVTable, TypeId});
+        Builder.CreateCall(CGM.getIntrinsic(IID), {CastedVTable, TypeId});
     Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::assume), TypeTest);
   }
 }