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

[Timm Baeder via cfe-commits]

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

>From f1c2dbfd29b201baf644d7f7e5ee5dd2a9f1f744 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbae...@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:

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