Avoid nullptr dereferencing of 'SubExpr'; NFC

[schittir]

Summary

Avoid nullptr dereferencing of 'Constraint'; NFC

Klocwork static code analysis exposed this bug:
Pointer 'SubExpr' returned from call to getSubExpr() function
which may return NULL from 'cast_or_null<Expr>(Operand)',
which will be dereferenced in the statement following it

Add an assert on SubExpr to avoid nullptr dereferencing

[aaron.ballman]

LGTM! There is no way for this to be null because emitRethrow() is what should be called in that case.

I'll land this on your behalf sometime shortly (perhaps as late as tomorrow).

[schittir]

In D108712#2965433, @aaron.ballman wrote:

LGTM! There is no way for this to be null because emitRethrow() is what should be called in that case.

I'll land this on your behalf sometime shortly (perhaps as late as tomorrow).

Thank you, Aaron!

[aaron.ballman]

I've committed on your behalf in de15979bc32d761c9b5071fb7d28d7c04ebbfaf3, thank you for the improvement!

clang/lib/CodeGen/MicrosoftCXXABI.cpp

llvm::GlobalVariable *MicrosoftCXXABI::getThrowInfo(QualType T) {
   GV->setSection(".xdata");
   if (GV->isWeakForLinker())
     GV->setComdat(CGM.getModule().getOrInsertComdat(GV->getName()));
   return GV;
 }
 
 void MicrosoftCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
   const Expr *SubExpr = E->getSubExpr();
+  assert(SubExpr && "SubExpr cannot be null");
   QualType ThrowType = SubExpr->getType();
   // The exception object lives on the stack and it's address is passed to the
   // runtime function.
   Address AI = CGF.CreateMemTemp(ThrowType);
   CGF.EmitAnyExprToMem(SubExpr, AI, ThrowType.getQualifiers(),
                        /*IsInit=*/true);
 
   // The so-called ThrowInfo is used to describe how the exception object may be