[clang] [clang][bytecode] Fix a crash in overflow builtins (PR #147189)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/147189

Only initialize pointers that can be initialized.

>From 3a2009eb23c0ffab62103c0097a9cb273d315efe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sun, 6 Jul 2025 15:19:09 +0200
Subject: [PATCH] [clang][bytecode] Fix a crash in overflow builtins

Only initialize pointers that can be initialized.
---
 clang/lib/AST/ByteCode/InterpBuiltin.cpp      | 4 +++-
 clang/test/AST/ByteCode/builtin-functions.cpp | 8 ++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index a73fc6c7bf2b3..907b6c79a377f 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -861,7 +861,9 @@ static bool interp__builtin_overflowop(InterpState &S, CodePtr OpPC,
 
   // Write Result to ResultPtr and put Overflow on the stack.
   assignInteger(S, ResultPtr, ResultT, Result);
-  ResultPtr.initialize();
+  if (ResultPtr.canBeInitialized())
+    ResultPtr.initialize();
+
   assert(Call->getDirectCallee()->getReturnType()->isBooleanType());
   S.Stk.push<Boolean>(Overflow);
   return true;
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 3b95a8ea48596..1bb6d22db9823 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -1753,4 +1753,12 @@ namespace I128Mul {
 }
 #endif
 
+namespace InitParam {
+  constexpr int foo(int a) {
+      __builtin_mul_overflow(20, 10, &a);
+      return a;
+  }
+  static_assert(foo(10) == 200);
+}
+
 #endif