[clang] [clang][bytecode] Use a special opcode for trivial defaulted copy/move operator calls (PR #222332)

[Oliver Hunt via cfe-commits]

================
@@ -3404,6 +3404,64 @@ std::optional<Pointer> addSubOffsetOpaque(InterpState &S, CodePtr OpPC,
   return Pointer(OP.withPastEnd(true), NewOffset);
 }
 
+bool Memcpy(InterpState &S, CodePtr OpPC) {
+  const Pointer &Src = S.Stk.pop<Pointer>();
+  Pointer &Dest = S.Stk.peek<Pointer>();
+
+  if (Src.isDummy() || !Src.isBlockPointer())
+    return false;
+  if (!Dest.isBlockPointer())
+    return false;
+
+  if ((Src.getRecord() && Src.getRecord()->isUnion() &&
+       !Src.getRecord()->isAnonymousUnion()) ||
+      Src.inUnion()) {
+    if (!CheckLoad(S, OpPC, Src))
+      return false;
+  }
+
+  return DoMemcpy(S, OpPC, Src, Dest);
+}
+
+bool TrivialCopy(InterpState &S, CodePtr OpPC, bool Activate,
+                 const Function *Func) {
+  const Pointer &Src = S.Stk.pop<Pointer>();
+  Pointer &Dest = S.Stk.peek<Pointer>();
+
+  if (Src.isDummy() || Src.isConstexprUnknown() || !Src.isBlockPointer())
+    return false;
+  if (!Dest.isBlockPointer() || Dest.isDummy() || Dest.isConstexprUnknown())
+    return false;
+
+  if (!CheckStore(S, OpPC, Dest, AK_MemberCall,
+                  /*WillBeActivated=*/Activate))
+    return false;
+
+  if (S.checkingPotentialConstantExpression())
+    return false;
+
+  // NOTE: This is a fake function frame that doesn't do anything except show up
+  // in the "in call to" diagnostics. Since the copies we replace with this
+  // opcode are always defaulted/trivial, they don't add much there either
+  // though. Once we default to the bytecode interpreter, we shoud consider just
+  // removing it.
+  auto Memory = std::make_unique<char[]>(InterpFrame::allocSize(Func));
+  auto *NewFrame =
+      new (Memory.get()) InterpFrame(S, Func, S.PC, /*VarArgSize=*/0);
+  InterpFrame *FrameBefore = S.Current;
+  S.Current = NewFrame;
----------------
ojhunt wrote:

Not for this PR, but it does feel like having an RAII type to manage this would be nice

https://github.com/llvm/llvm-project/pull/222332