[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
diff --git a/clang/lib/CodeGen/CGCleanup.cpp b/clang/lib/CodeGen/CGCleanup.cpp
index 5e01100..70eaa32 100644
--- a/clang/lib/CodeGen/CGCleanup.cpp
+++ b/clang/lib/CodeGen/CGCleanup.cpp
@@ -860,6 +860,9 @@
// TODO: base this on the number of branch-afters and fixups
const unsigned SwitchCapacity = 10;
+ // pass the abnormal exit flag to Fn (SEH cleanup)
+ cleanupFlags.setHasExitSwitch();
+
llvm::LoadInst *Load =
createLoadInstBefore(getNormalCleanupDestSlot(), "cleanup.dest",
nullptr);
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 @@
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]);
diff --git a/clang/lib/CodeGen/EHScopeStack.h b/clang/lib/CodeGen/EHScopeStack.h
index 0ed67aa..0fa0b54 100644
--- a/clang/lib/CodeGen/EHScopeStack.h
+++ b/clang/lib/CodeGen/EHScopeStack.h
@@ -158,9 +158,10 @@
/// Generation flags.
class Flags {
enum {
- F_IsForEH = 0x1,
+ F_IsForEH = 0x1,
F_IsNormalCleanupKind = 0x2,
- F_IsEHCleanupKind = 0x4
+ F_IsEHCleanupKind = 0x4,
+ F_HasExitSwitch = 0x8,
};
unsigned flags;
@@ -179,8 +180,10 @@
/// cleanup.
bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
- };
+ bool hasExitSwitch() const { return flags & F_HasExitSwitch; }
+ void setHasExitSwitch() { flags |= F_HasExitSwitch; }
+ };
/// Emit the cleanup. For normal cleanups, this is run in the
/// same EH context as when the cleanup was pushed, i.e. the