CodeGen: ensure placeholder instruction for cleanup is created

A placeholder instruction for use in generation of cleanup code for an
initializer list would not be emitted if the base class contained a
non-trivial destructor and the class contains no fields of its own. This
would be the case when using CTAD to deduce the template arguments for a
struct with an overloaded call operator, e.g.

```
template <class... Ts> struct ctad : Ts... {};
template <class... Ts> ctad(Ts...)->ctad<Ts...>;
```

and this class was initialized with a list of lambdas capturing by copy,
e.g.

```
ctad c {[s](short){}, [s](long){}};
```

In a release build the bug would manifest itself as a crash in the SROA
pass, however, in a debug build the following assert in CGCleanup.cpp
would fail:

```
assert(dominatingIP && "no existing variable and no dominating IP!");
```

By ensuring that a placeholder instruction is emitted even if there's no
fields in the class, neither the assert nor the crash is reproducible.

See https://bugs.llvm.org/show_bug.cgi?id=40771

Patch by Øystein Dale!

llvm-svn: 367042

1 files changed, 11 insertions, 8 deletions

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 695facd50b6..0a57870a7c5 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1495,6 +1495,13 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
   // initializers throws an exception.
   SmallVector<EHScopeStack::stable_iterator, 16> cleanups;
   llvm::Instruction *cleanupDominator = nullptr;
+  auto addCleanup = [&](const EHScopeStack::stable_iterator &cleanup) {
+    cleanups.push_back(cleanup);
+    if (!cleanupDominator) // create placeholder once needed
+      cleanupDominator = CGF.Builder.CreateAlignedLoad(
+          CGF.Int8Ty, llvm::Constant::getNullValue(CGF.Int8PtrTy),
+          CharUnits::One());
+  };
 
   unsigned curInitIndex = 0;
 
@@ -1519,7 +1526,7 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
       if (QualType::DestructionKind dtorKind =
               Base.getType().isDestructedType()) {
         CGF.pushDestroy(dtorKind, V, Base.getType());
-        cleanups.push_back(CGF.EHStack.stable_begin());
+        addCleanup(CGF.EHStack.stable_begin());
       }
     }
   }
@@ -1596,15 +1603,9 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
           = field->getType().isDestructedType()) {
       assert(LV.isSimple());
       if (CGF.needsEHCleanup(dtorKind)) {
-        if (!cleanupDominator)
-          cleanupDominator = CGF.Builder.CreateAlignedLoad(
-              CGF.Int8Ty,
-              llvm::Constant::getNullValue(CGF.Int8PtrTy),
-              CharUnits::One()); // placeholder
-
         CGF.pushDestroy(EHCleanup, LV.getAddress(), field->getType(),
                         CGF.getDestroyer(dtorKind), false);
-        cleanups.push_back(CGF.EHStack.stable_begin());
+        addCleanup(CGF.EHStack.stable_begin());
         pushedCleanup = true;
       }
     }
@@ -1620,6 +1621,8 @@ void AggExprEmitter::VisitInitListExpr(InitListExpr *E) {
 
   // Deactivate all the partial cleanups in reverse order, which
   // generally means popping them.
+  assert((cleanupDominator || cleanups.empty()) &&
+         "Missing cleanupDominator before deactivating cleanup blocks");
   for (unsigned i = cleanups.size(); i != 0; --i)
     CGF.DeactivateCleanupBlock(cleanups[i-1], cleanupDominator);