[clang] [clang][bytecode] Make some builtins no-ops (PR #141952)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/141952

For some builtins, we dont' need to do anything, but due to the cleanup code being the same for all builtins, we still had to duplicate the value on the stack. Remove that and get rid of all the unnecessary pressure on the InterpStack.

>From e06d1414f4be0830b5498b9a70ea62f14f6096dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 29 May 2025 13:48:15 +0200
Subject: [PATCH] [clang][bytecode] Make some builtins no-ops

For some builtins, we dont' need to do anything, but due to the cleanup
code being the same for all builtins, we still had to duplicate the
value on the stack. Remove that and get rid of all the unnecessary
pressure on the InterpStack.
---
 clang/lib/AST/ByteCode/InterpBuiltin.cpp | 46 +++++++++++++-----------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 8edc6248dcbfd..ba38fc505e3b4 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -23,6 +23,24 @@
 namespace clang {
 namespace interp {
 
+static bool isNoopBuiltin(unsigned ID) {
+  switch (ID) {
+  case Builtin::BIas_const:
+  case Builtin::BIforward:
+  case Builtin::BIforward_like:
+  case Builtin::BImove:
+  case Builtin::BImove_if_noexcept:
+  case Builtin::BIaddressof:
+  case Builtin::BI__addressof:
+  case Builtin::BI__builtin_addressof:
+  case Builtin::BI__builtin_launder:
+    return true;
+  default:
+    return false;
+  }
+  return false;
+}
+
 static unsigned callArgSize(const InterpState &S, const CallExpr *C) {
   unsigned O = 0;
 
@@ -100,6 +118,8 @@ static bool retBI(InterpState &S, const CallExpr *Call, unsigned BuiltinID) {
 static bool retPrimValue(InterpState &S, CodePtr OpPC,
                          std::optional<PrimType> &T, const CallExpr *Call,
                          unsigned BuiltinID) {
+  if (isNoopBuiltin(BuiltinID))
+    return true;
 
   if (!T) {
     if (!Context::isUnevaluatedBuiltin(BuiltinID)) {
@@ -742,24 +762,14 @@ static bool interp__builtin_addressof(InterpState &S, CodePtr OpPC,
                                       const CallExpr *Call) {
   assert(Call->getArg(0)->isLValue());
   PrimType PtrT = S.getContext().classify(Call->getArg(0)).value_or(PT_Ptr);
-
-  if (PtrT == PT_Ptr) {
-    const Pointer &Arg = S.Stk.peek<Pointer>();
-    S.Stk.push<Pointer>(Arg);
-  } else {
-    assert(false && "Unsupported pointer type passed to __builtin_addressof()");
-  }
+  assert(PtrT == PT_Ptr &&
+         "Unsupported pointer type passed to __builtin_addressof()");
   return true;
 }
 
 static bool interp__builtin_move(InterpState &S, CodePtr OpPC,
                                  const InterpFrame *Frame,
                                  const CallExpr *Call) {
-
-  PrimType ArgT = S.getContext().classify(Call->getArg(0)).value_or(PT_Ptr);
-
-  TYPE_SWITCH(ArgT, const T &Arg = S.Stk.peek<T>(); S.Stk.push<T>(Arg););
-
   return Call->getDirectCallee()->isConstexpr();
 }
 
@@ -775,13 +785,6 @@ static bool interp__builtin_eh_return_data_regno(InterpState &S, CodePtr OpPC,
   return true;
 }
 
-/// Just takes the first Argument to the call and puts it on the stack.
-static bool noopPointer(InterpState &S) {
-  const Pointer &Arg = S.Stk.peek<Pointer>();
-  S.Stk.push<Pointer>(Arg);
-  return true;
-}
-
 // Two integral values followed by a pointer (lhs, rhs, resultOut)
 static bool interp__builtin_overflowop(InterpState &S, CodePtr OpPC,
                                        const CallExpr *Call,
@@ -2504,6 +2507,7 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
   case Builtin::BIaddressof:
   case Builtin::BI__addressof:
   case Builtin::BI__builtin_addressof:
+    assert(isNoopBuiltin(BuiltinID));
     if (!interp__builtin_addressof(S, OpPC, Frame, Call))
       return false;
     break;
@@ -2513,6 +2517,7 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
   case Builtin::BIforward_like:
   case Builtin::BImove:
   case Builtin::BImove_if_noexcept:
+    assert(isNoopBuiltin(BuiltinID));
     if (!interp__builtin_move(S, OpPC, Frame, Call))
       return false;
     break;
@@ -2523,8 +2528,7 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
     break;
 
   case Builtin::BI__builtin_launder:
-    if (!noopPointer(S))
-      return false;
+    assert(isNoopBuiltin(BuiltinID));
     break;
 
   case Builtin::BI__builtin_add_overflow: