[Openmp-commits] [openmp] [OpenMP] Basic BumpAllocator for (AMD)GPUs (PR #69806)

[Johannes Doerfert via Openmp-commits]

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@@ -0,0 +1,80 @@
+//===------ State.cpp - OpenMP State & ICV interface ------------- 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
+//
+//===----------------------------------------------------------------------===//
+//
+//===----------------------------------------------------------------------===//
+
+#include "Allocator.h"
+#include "Configuration.h"
+#include "Environment.h"
+#include "Mapping.h"
+#include "Synchronization.h"
+#include "Types.h"
+#include "Utils.h"
+
+using namespace ompx;
+
+#pragma omp begin declare target device_type(nohost)
+
+[[gnu::used, gnu::retain, gnu::weak,
+  gnu::visibility(
+      "protected")]] DeviceMemoryPoolTy __omp_rtl_device_memory_pool;
+[[gnu::used, gnu::retain, gnu::weak,
+  gnu::visibility("protected")]] DeviceMemoryPoolTrackingTy
+    __omp_rtl_device_memory_pool_tracker;
+
+/// Stateless bump allocator that uses the __omp_rtl_device_memory_pool
+/// directly.
+struct BumpAllocatorTy final {
+
+  void *alloc(uint64_t Size) {
+    Size = utils::roundUp(Size, uint64_t(allocator::ALIGNMENT));
+
+    if (config::isDebugMode(DeviceDebugKind::AllocationTracker)) {
+      atomic::add(&__omp_rtl_device_memory_pool_tracker.NumAllocations, 1,
+                  atomic::seq_cst);
+      atomic::add(&__omp_rtl_device_memory_pool_tracker.AllocationTotal, Size,
+                  atomic::seq_cst);
+      atomic::min(&__omp_rtl_device_memory_pool_tracker.AllocationMin, Size,
+                  atomic::seq_cst);
+      atomic::max(&__omp_rtl_device_memory_pool_tracker.AllocationMax, Size,
+                  atomic::seq_cst);
+    }
+
+    uint64_t *Data =
+        reinterpret_cast<uint64_t *>(&__omp_rtl_device_memory_pool.Ptr);
+    uint64_t End =
+        reinterpret_cast<uint64_t>(Data) + __omp_rtl_device_memory_pool.Size;
+
+    uint64_t OldData = atomic::add(Data, Size, atomic::seq_cst);
+    if (OldData + Size > End)
+      __builtin_trap();
----------------
jdoerfert wrote:

> True, but I figured the inevitable dereference of the nullptr would be a good trap that's usually more easily connected with malloc.

That is arguably not true, especially for "implicit"/"hidden" mallocs. People that run on AMD complain often about tests not running, or only running with O1/2/3 but don't connect it to the malloc. The problem with `*nullptr` is that it's UB. So we don't necessarily do it at all. I have seen many tests "pass" even though the smart stack was full but the fallback to malloc was removed and somehow writing some shared memory worked out. But that also leads to spurious fails. Let's crash loud and fast, not via silent corruption.

https://github.com/llvm/llvm-project/pull/69806