[clang] [Clang][Interp] `__builtin_os_log_format_buffer_size` should be an unevaluated builtin (PR #99895)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (yronglin)

<details>
<summary>Changes</summary>

Follow the current behavior of constant evaluator, `__builtin_os_log_format_buffer_size` should be an unevaluated builtin.

The following code is well-formed:
```
void test_builtin_os_log(void *buf, int i, const char *data) {
  constexpr int len = __builtin_os_log_format_buffer_size("%d %{public}s %{private}.16P", i, data, data);
}
```

---
Full diff: https://github.com/llvm/llvm-project/pull/99895.diff


2 Files Affected:

- (modified) clang/lib/AST/Interp/ByteCodeEmitter.cpp (+2-1) 
- (modified) clang/test/CodeGen/builtins.c (+1) 


``````````diff
diff --git a/clang/lib/AST/Interp/ByteCodeEmitter.cpp b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
index a3d4c7d7392da..fee4432a8f661 100644
--- a/clang/lib/AST/Interp/ByteCodeEmitter.cpp
+++ b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
@@ -27,7 +27,8 @@ using namespace clang::interp;
 /// Similar information is available via ASTContext::BuiltinInfo,
 /// but that is not correct for our use cases.
 static bool isUnevaluatedBuiltin(unsigned BuiltinID) {
-  return BuiltinID == Builtin::BI__builtin_classify_type;
+  return BuiltinID == Builtin::BI__builtin_classify_type ||
+         BuiltinID == Builtin::BI__builtin_os_log_format_buffer_size;
 }
 
 Function *ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
diff --git a/clang/test/CodeGen/builtins.c b/clang/test/CodeGen/builtins.c
index b41efb59e61db..1f998236501d2 100644
--- a/clang/test/CodeGen/builtins.c
+++ b/clang/test/CodeGen/builtins.c
@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -emit-llvm -o %t %s
 // RUN: not grep __builtin %t
 // RUN: %clang_cc1 -emit-llvm -triple x86_64-darwin-apple -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-darwin-apple -fexperimental-new-constant-interpreter -o - %s | FileCheck %s
 
 int printf(const char *, ...);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/99895