[clang] [clang][bytecode] Fix a crash in __builtin_subcb (PR #199400)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

Don't try to initialize pointers that can't be initialized

---
Full diff: https://github.com/llvm/llvm-project/pull/199400.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/InterpBuiltin.cpp (+2-1) 
- (modified) clang/test/AST/ByteCode/builtin-functions.cpp (+7) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 3e9ce902427eb..863a25f519e9b 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -1019,7 +1019,8 @@ static bool interp__builtin_carryop(InterpState &S, CodePtr OpPC,
   QualType CarryOutType = Call->getArg(3)->getType()->getPointeeType();
   PrimType CarryOutT = *S.getContext().classify(CarryOutType);
   assignIntegral(S, CarryOutPtr, CarryOutT, CarryOut);
-  CarryOutPtr.initialize();
+  if (CarryOutPtr.canBeInitialized())
+    CarryOutPtr.initialize();
 
   assert(Call->getType() == Call->getArg(0)->getType());
   pushInteger(S, Result, Call->getType());
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 97fa1760ee167..7b19c3388e7cd 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -2048,3 +2048,10 @@ namespace WcslenInvalidArg {
   static_assert(__builtin_wcslen(L"x") == 1);
 
 }
+
+namespace SubCb {
+  constexpr unsigned char subcb(unsigned char lhs, unsigned char rhs, unsigned char carry) {
+    return __builtin_subcb(lhs, rhs, carry, &rhs);
+  }
+  static_assert(subcb(10, 15, 1) == 250);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/199400