[Windows SEH] Fix abnormal-exits in _try

Summary:
Per Windows SEH Spec, except _leave, all other early exits of a _try (goto/return/continue/break) are considered abnormal exits.  In those cases, the first parameter passes to its _finally funclet should be TRUE to indicate an abnormal-termination.

One way to implement abnormal exits in _try is to invoke Windows runtime _local_unwind() (MSVC approach) that will invoke _dtor funclet where abnormal-termination flag is always TRUE when calling _finally.  Obviously this approach is less optimal and is complicated to implement in Clang.

Clang today has a NormalCleanupDestSlot mechanism to dispatch multiple exits at the end of _try.  Since  _leave (or try-end fall-through) is always Indexed with 0 in that NormalCleanupDestSlot,  this fix takes the advantage of that mechanism and just passes NormalCleanupDest ID as 1st Arg to _finally.

Reviewers: rnk, eli.friedman, JosephTremoulet, asmith, efriedma

Reviewed By: efriedma

Subscribers: efriedma, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77936

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index a542c3d..a5dae1b 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -1639,6 +1639,19 @@ struct PerformSEHFinally final : EHScopeStack::Cleanup {
 
     llvm::Value *IsForEH =
         llvm::ConstantInt::get(CGF.ConvertType(ArgTys[0]), F.isForEHCleanup());
+
+    // Except _leave and fall-through at the end, all other exits in a _try
+    //   (return/goto/continue/break) are considered as abnormal terminations
+    //   since _leave/fall-through is always Indexed 0,
+    //   just use NormalCleanupDestSlot (>= 1 for goto/return/..),
+    //   as 1st Arg to indicate abnormal termination
+    if (!F.isForEHCleanup() && F.hasExitSwitch()) {
+      Address Addr = CGF.getNormalCleanupDestSlot();
+      llvm::Value *Load = CGF.Builder.CreateLoad(Addr, "cleanup.dest");
+      llvm::Value *Zero = llvm::Constant::getNullValue(CGM.Int32Ty);
+      IsForEH = CGF.Builder.CreateICmpNE(Load, Zero);
+    }
+
     Args.add(RValue::get(IsForEH), ArgTys[0]);
     Args.add(RValue::get(FP), ArgTys[1]);