[compiler-rt] [ctxprof] Auto root detection: trie for stack samples (PR #133106)

[Kazu Hirata via llvm-commits]

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@@ -0,0 +1,68 @@
+/*===- RootAutodetector.h- auto-detect roots for ctxprof  -----------------===*\
+|*
+|* 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 CTX_PROFILE_ROOTAUTODETECTOR_H_
+#define CTX_PROFILE_ROOTAUTODETECTOR_H_
+
+#include "sanitizer_common/sanitizer_dense_map.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+#include "sanitizer_common/sanitizer_stacktrace.h"
+#include <pthread.h>
+#include <sanitizer/common_interface_defs.h>
+
+using namespace __asan;
+using namespace __sanitizer;
+
+namespace __ctx_profile {
+
+template <typename T> using Set = DenseMap<T, bool>;
+
+/// A trie. A node is the address of a callsite in a function activation. A
+/// child is a callsite in the activation made from the callsite corresponding
+/// to the parent.
+class Trie final {
+  friend class PerThreadCallsiteTrie;
+  const uptr CallsiteAddress;
+  uint64_t Count = 0;
+  DenseMap<uptr, Trie> Children;
+
+public:
+  uptr address() const { return CallsiteAddress; }
+  uint64_t count() const { return Count; }
+  const DenseMap<uptr, Trie> &children() const { return Children; }
+
+  Trie(uptr CallsiteAddress) : CallsiteAddress(CallsiteAddress) {}
+};
+
+/// Capture all the stack traces observed for a specific thread. The "for a
+/// specific thread" part is not enforced, but assumed in determineRoots.
+class PerThreadCallsiteTrie {
+  Trie T;
+
+protected:
+  /// Return the runtime start address of the function that contains the call at
+  /// the runtime address CallsiteAddress. May be overriden for easy testing.
+  virtual uptr getFctStartAddr(uptr CallsiteAddress) const;
+
+public:
+  PerThreadCallsiteTrie(const PerThreadCallsiteTrie &) = delete;
+  PerThreadCallsiteTrie(PerThreadCallsiteTrie &&) = default;
+  PerThreadCallsiteTrie() : T(0) {}
----------------
kazutakahirata wrote:

nit: May I suggest the following?

```suggestion
  PerThreadCallsiteTrie() = default;
```

while adding a suitable default constructor to `Trie`?


https://github.com/llvm/llvm-project/pull/133106