[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, 3 insertions, 0 deletions

diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index e248e58..2e32469 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -40,6 +40,7 @@
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Transforms/IPO/WholeProgramDevirt.h"
 #include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
 #include "llvm/Transforms/Utils/SplitModule.h"
@@ -560,6 +561,8 @@ Error lto::thinBackend(const Config &Conf, unsigned Task, AddStreamFn AddStream,
   // the module, if applicable.
   Mod.setPartialSampleProfileRatio(CombinedIndex);
 
+  updatePublicTypeTestCalls(Mod, CombinedIndex.withWholeProgramVisibility());
+
   if (Conf.CodeGenOnly) {
     codegen(Conf, TM.get(), AddStream, Task, Mod, CombinedIndex);
     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));