[compiler-rt] [NFC][asan] Cleanup AsanThreadIdAndName ctor/init (PR #111923)

[Vitaly Buka via llvm-commits]

https://github.com/vitalybuka updated https://github.com/llvm/llvm-project/pull/111923

>From 5e9272e50610634f1b0c42aaad47d0f90a8c9762 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Thu, 10 Oct 2024 16:38:23 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20change?=
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Created using spr 1.3.4

[skip ci]
---
 compiler-rt/lib/asan/asan_descriptions.cpp | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/compiler-rt/lib/asan/asan_descriptions.cpp b/compiler-rt/lib/asan/asan_descriptions.cpp
index 1c2f20a76343bb..674fe9c1e90be0 100644
--- a/compiler-rt/lib/asan/asan_descriptions.cpp
+++ b/compiler-rt/lib/asan/asan_descriptions.cpp
@@ -48,9 +48,20 @@ void DescribeThread(AsanThreadContext *context) {
     return;
   }
   context->announced = true;
+
+  AsanThreadContext *parent_context =
+      context->parent_tid == kInvalidTid
+          ? nullptr
+          : GetThreadContextByTidLocked(context->parent_tid);
+
+  // `context->parent_tid` may point to reused slot. Check `unique_id` which
+  // is always smaller for the parent, always greater for a new user.
+  if (context->unique_id <= parent_context->unique_id)
+    parent_context = nullptr;
+
   InternalScopedString str;
   str.AppendF("Thread %s", AsanThreadIdAndName(context).c_str());
-  if (context->parent_tid == kInvalidTid) {
+  if (!parent_context) {
     str.Append(" created by unknown thread\n");
     Printf("%s", str.data());
     return;
@@ -60,11 +71,8 @@ void DescribeThread(AsanThreadContext *context) {
   Printf("%s", str.data());
   StackDepotGet(context->stack_id).Print();
   // Recursively described parent thread if needed.
-  if (flags()->print_full_thread_history) {
-    AsanThreadContext *parent_context =
-        GetThreadContextByTidLocked(context->parent_tid);
+  if (flags()->print_full_thread_history)
     DescribeThread(parent_context);
-  }
 }
 
 // Shadow descriptions