[libcxx-commits] [libcxx] [libc++][pstl] Make the serial backend the ultimate fallback for all backends (PR #233421)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Michael G. Kazakov (mikekazakov)

<details>
<summary>Changes</summary>

Always fall back to the serial backend as a last resort when an algorithm implementation was not found.
This is a preparation before exposing a bunch of PSTL algorithms we don't currently intend to parallelise.

Fixes #<!-- -->229813

---
Full diff: https://github.com/llvm/llvm-project/pull/233421.diff


2 Files Affected:

- (modified) libcxx/include/__pstl/backend.h (+2) 
- (modified) libcxx/include/__pstl/backend_fwd.h (+2-2) 


``````````diff
diff --git a/libcxx/include/__pstl/backend.h b/libcxx/include/__pstl/backend.h
index 5980b0708cd34..8708e492fcc23 100644
--- a/libcxx/include/__pstl/backend.h
+++ b/libcxx/include/__pstl/backend.h
@@ -26,10 +26,12 @@ _LIBCPP_PUSH_MACROS
 #    include <__pstl/backends/serial.h>
 #  elif defined(_LIBCPP_PSTL_BACKEND_STD_THREAD)
 #    include <__pstl/backends/default.h>
+#    include <__pstl/backends/serial.h>
 #    include <__pstl/backends/std_thread.h>
 #  elif defined(_LIBCPP_PSTL_BACKEND_LIBDISPATCH)
 #    include <__pstl/backends/default.h>
 #    include <__pstl/backends/libdispatch.h>
+#    include <__pstl/backends/serial.h>
 #  endif
 
 #endif // _LIBCPP_STD_VER >= 17
diff --git a/libcxx/include/__pstl/backend_fwd.h b/libcxx/include/__pstl/backend_fwd.h
index e45943954bed9..8bb23f352c923 100644
--- a/libcxx/include/__pstl/backend_fwd.h
+++ b/libcxx/include/__pstl/backend_fwd.h
@@ -56,10 +56,10 @@ struct __std_thread_backend_tag;
 using __current_configuration _LIBCPP_NODEBUG = __backend_configuration<__serial_backend_tag, __default_backend_tag>;
 #  elif defined(_LIBCPP_PSTL_BACKEND_STD_THREAD)
 using __current_configuration _LIBCPP_NODEBUG =
-    __backend_configuration<__std_thread_backend_tag, __default_backend_tag>;
+    __backend_configuration<__std_thread_backend_tag, __default_backend_tag, __serial_backend_tag>;
 #  elif defined(_LIBCPP_PSTL_BACKEND_LIBDISPATCH)
 using __current_configuration _LIBCPP_NODEBUG =
-    __backend_configuration<__libdispatch_backend_tag, __default_backend_tag>;
+    __backend_configuration<__libdispatch_backend_tag, __default_backend_tag, __serial_backend_tag>;
 #  else
 
 // ...New vendors can add parallel backends here...

``````````

</details>


https://github.com/llvm/llvm-project/pull/233421