[libcxx-commits] [libcxx] [libc++] Fix "leak" of PMR resource in benchmark (PR #216114)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

<details>
<summary>Changes</summary>

The benchmark was not releasing the monotonic buffer resource, which means we'd grow a larger and larger pool as Google Benchmark would go through more and more iterations of the benchmark.

As a drive-by, it also fixes an incorrect `DoNotOptimize(c + i)` that was called on the wrong pointer (c is a pointer to bytes).

---
Full diff: https://github.com/llvm/llvm-project/pull/216114.diff


1 Files Affected:

- (modified) libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h (+7-4) 


``````````diff
diff --git a/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h b/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
index 34cd1ca90b647..4eaac2bff038b 100644
--- a/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
+++ b/libcxx/test/benchmarks/containers/associative/associative_container_benchmarks.h
@@ -147,18 +147,21 @@ void associative_container_benchmarks(std::string container) {
     std::pmr::monotonic_buffer_resource rs2(size * 64 * BatchSize); // 64 bytes should be enough per node
     while (st.KeepRunningBatch(BatchSize)) {
       for (std::size_t i = 0; i != BatchSize; ++i) {
-        new (c + i * sizeof(PMRContainer)) PMRContainer(std::move(srcs[i]), &rs2);
-        benchmark::DoNotOptimize(c + i);
+        PMRContainer* p = reinterpret_cast<PMRContainer*>(c) + i;
+        new (p) PMRContainer(std::move(srcs[i]), &rs2);
+        benchmark::DoNotOptimize(p);
         benchmark::ClobberMemory();
       }
 
       st.PauseTiming();
       for (std::size_t i = 0; i != BatchSize; ++i) {
-        reinterpret_cast<PMRContainer*>(c + i * sizeof(PMRContainer))->~PMRContainer();
+        PMRContainer* p = reinterpret_cast<PMRContainer*>(c) + i;
+        p->~PMRContainer();
       }
       rs2.release();
       srcs.clear();
-      for (size_t i = 0; i != BatchSize; ++i)
+      rs.release();
+      for (std::size_t i = 0; i != BatchSize; ++i)
         srcs.emplace_back(&rs).insert(in.begin(), in.end());
 
       st.ResumeTiming();

``````````

</details>


https://github.com/llvm/llvm-project/pull/216114