[libc-commits] [libc] dc9baac - [libc] Partially implement `atexit` on the GPU

[Joseph Huber via libc-commits]

Author: Joseph Huber
Date: 2023-04-26T16:52:32-05:00
New Revision: dc9baac1a0148ce0c2b8afdc75e3e208597f79c9

URL: https://github.com/llvm/llvm-project/commit/dc9baac1a0148ce0c2b8afdc75e3e208597f79c9
DIFF: https://github.com/llvm/llvm-project/commit/dc9baac1a0148ce0c2b8afdc75e3e208597f79c9.diff

LOG: [libc] Partially implement `atexit` on the GPU

The `atexit` function controls registering functions to call at the end
of the program. This is difficult to do in general on the GPU because of
the lack of a real mutex implementation. We primarily provide this for
testing where we can explicitly restrict how the `atexit` registration
functions are called. So we simply create a passthrough Mutex to get
past the usage of it as per @sivachandra's suggestion.

Depends on D149225

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D149226

Added: 
    libc/src/__support/threads/gpu/CMakeLists.txt
    libc/src/__support/threads/gpu/mutex.h

Modified: 
    libc/config/gpu/api.td
    libc/config/gpu/entrypoints.txt
    libc/src/__support/threads/mutex.h

Removed: 
    


################################################################################
diff  --git a/libc/config/gpu/api.td b/libc/config/gpu/api.td
index 9036bbc89238..3e6927de9463 100644
--- a/libc/config/gpu/api.td
+++ b/libc/config/gpu/api.td
@@ -5,3 +5,10 @@ include "spec/stdc.td"
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
 }
+
+def StdlibAPI : PublicAPI<"stdlib.h"> {
+  let Types = [
+    "size_t",
+    "__atexithandler_t",
+  ];
+}

diff  --git a/libc/config/gpu/entrypoints.txt b/libc/config/gpu/entrypoints.txt
index d42a554577e6..c5ed1e3dd476 100644
--- a/libc/config/gpu/entrypoints.txt
+++ b/libc/config/gpu/entrypoints.txt
@@ -56,9 +56,11 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # stdlib.h entrypoints
     libc.src.stdlib.atoi
+    libc.src.stdlib.atexit
 
     # Only implemented in the test suite
     libc.src.stdlib.malloc
+    libc.src.stdlib.aligned_alloc
     libc.src.stdlib.realloc
     libc.src.stdlib.free
 

diff  --git a/libc/src/__support/threads/gpu/CMakeLists.txt b/libc/src/__support/threads/gpu/CMakeLists.txt
new file mode 100644
index 000000000000..ea89feb0c5c6
--- /dev/null
+++ b/libc/src/__support/threads/gpu/CMakeLists.txt
@@ -0,0 +1,5 @@
+add_header_library(
+  mutex
+  HDRS
+    mutex.h
+)

diff  --git a/libc/src/__support/threads/gpu/mutex.h b/libc/src/__support/threads/gpu/mutex.h
new file mode 100644
index 000000000000..c4a75907eed7
--- /dev/null
+++ b/libc/src/__support/threads/gpu/mutex.h
@@ -0,0 +1,31 @@
+//===--- Implementation of a GPU mutex class --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_THREAD_GPU_MUTEX_H
+#define LLVM_LIBC_SRC_SUPPORT_THREAD_GPU_MUTEX_H
+
+#include "src/__support/macros/attributes.h"
+#include "src/__support/threads/mutex_common.h"
+
+namespace __llvm_libc {
+
+/// Implementation of a simple passthrough mutex which guards nothing. A
+/// complete Mutex locks in general cannot be implemented on the GPU. We simply
+/// define the Mutex interface and require that only a single thread executes
+/// code requiring a mutex lock.
+struct Mutex {
+  LIBC_INLINE constexpr Mutex(bool, bool, bool) {}
+
+  LIBC_INLINE MutexError lock() { return MutexError::NONE; }
+  LIBC_INLINE MutexError unlock() { return MutexError::NONE; }
+  LIBC_INLINE MutexError reset() { return MutexError::NONE; }
+};
+
+} // namespace __llvm_libc
+
+#endif

diff  --git a/libc/src/__support/threads/mutex.h b/libc/src/__support/threads/mutex.h
index 1015333b677a..3c2291d8f41f 100644
--- a/libc/src/__support/threads/mutex.h
+++ b/libc/src/__support/threads/mutex.h
@@ -9,6 +9,8 @@
 #ifndef LLVM_LIBC_SRC_SUPPORT_THREAD_MUTEX_H
 #define LLVM_LIBC_SRC_SUPPORT_THREAD_MUTEX_H
 
+#include "src/__support/macros/properties/architectures.h"
+
 // Platform independent code will include this header file which pulls
 // the platfrom specific specializations using platform macros.
 //
@@ -35,8 +37,10 @@
 // few global locks. So, to avoid static initialization order fiasco, we
 // want the constructors of the Mutex classes to be constexprs.
 
-#ifdef __unix__
+#if defined(__unix__)
 #include "linux/mutex.h"
+#elif defined(LIBC_TARGET_ARCH_IS_GPU)
+#include "gpu/mutex.h"
 #endif // __unix__
 
 namespace __llvm_libc {