[clang][bytecode] Always track item types in InterpStack (#151088)

This has been a long-standing problem, but we didn't use to call the
destructors of items on the stack unless we explicitly `pop()` or
`discard()` them.

When interpretation was interrupted midway-through (because something
failed), we left `Pointer`s on the stack. Since all `Block`s track what
`Pointer`s point to them (via a doubly-linked list in the `Pointer`),
that meant we potentially leave deallocated pointers in that list. We
used to work around this by removing the `Pointer` from the list before
deallocating the block.

However, we now want to track pointers to global blocks as well, which
poses a problem since the blocks are never deallocated and thus those
pointers are always left dangling.

I've tried a few different approaches to fixing this but in the end I
just gave up on the idea of never knowing what items are in the stack.
We already have an `ItemTypes` vector that we use for debugging
assertions. This patch simply enables this vector unconditionally and
uses it in the abort case to properly `discard()` all elements from the
stack. That's a little sad IMO but I don't know of another way of
solving this problem.

As expected, this is a slight hit to compile times:
https://llvm-compile-time-tracker.com/compare.php?from=574d0a92060bf4808776b7a0239ffe91a092b15d&to=0317105f559093cfb909bfb01857a6b837991940&stat=instructions:u

1 files changed, 15 insertions, 10 deletions

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 5c41647..f2ce69a 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -2980,20 +2980,25 @@ bool Compiler<Emitter>::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
     if (T && !E->isLValue())
       return this->delegate(Init);
 
-    if (std::optional<unsigned> GlobalIndex = P.createGlobal(E)) {
-      if (!this->emitGetPtrGlobal(*GlobalIndex, E))
-        return false;
+    std::optional<unsigned> GlobalIndex = P.createGlobal(E);
+    if (!GlobalIndex)
+      return false;
 
-      if (T) {
-        if (!this->visit(Init))
-          return false;
-        return this->emitInitGlobal(*T, *GlobalIndex, E);
-      }
+    if (!this->emitGetPtrGlobal(*GlobalIndex, E))
+      return false;
+
+    // Since this is a global variable, we might've already seen,
+    // don't do it again.
+    if (P.isGlobalInitialized(*GlobalIndex))
+      return true;
 
-      return this->visitInitializer(Init) && this->emitFinishInit(E);
+    if (T) {
+      if (!this->visit(Init))
+        return false;
+      return this->emitInitGlobal(*T, *GlobalIndex, E);
     }
 
-    return false;
+    return this->visitInitializer(Init) && this->emitFinishInit(E);
   }
 
   // Otherwise, use a local variable.