[llvm-exegesis] Use LLVM Support to get thread ID

This patch switches from manually using the Linux syscall to get the
current thread ID to using the relevant LLVM Support libraries that
abstract over the low level system details.

Author: boomanaiden154

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

@@ -301,7 +301,7 @@ class SubProcessFunctionExecutorImpl
     if (AddMemDefError)
       return AddMemDefError;
 
-    long ParentTID = SubprocessMemory::getCurrentTID();
+    long ParentTID = get_threadid();
     pid_t ParentOrChildPID = fork();
 
     if (ParentOrChildPID == -1) {

llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp

@@ -10,6 +10,7 @@
 #include "Error.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/Threading.h"
 #include <cerrno>
 
 #ifdef __linux__
@@ -24,21 +25,14 @@ namespace exegesis {
 
 #if defined(__linux__) && !defined(__ANDROID__)
 
-long SubprocessMemory::getCurrentTID() {
-  // We're using the raw syscall here rather than the gettid() function provided
-  // by most libcs for compatibility as gettid() was only added to glibc in
-  // version 2.30.
-  return syscall(SYS_gettid);
-}
-
 Error SubprocessMemory::initializeSubprocessMemory(pid_t ProcessID) {
   // Add the PID to the shared memory name so that if we're running multiple
   // processes at the same time, they won't interfere with each other.
   // This comes up particularly often when running the exegesis tests with
   // llvm-lit. Additionally add the TID so that downstream consumers
   // using multiple threads don't run into conflicts.
   std::string AuxiliaryMemoryName =
-      formatv("/{0}auxmem{1}", getCurrentTID(), ProcessID);
+      formatv("/{0}auxmem{1}", get_threadid(), ProcessID);
   int AuxiliaryMemoryFD = shm_open(AuxiliaryMemoryName.c_str(),
                                    O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
   if (AuxiliaryMemoryFD == -1)
@@ -59,7 +53,7 @@ Error SubprocessMemory::addMemoryDefinition(
   SharedMemoryNames.reserve(MemoryDefinitions.size());
   for (auto &[Name, MemVal] : MemoryDefinitions) {
     std::string SharedMemoryName =
-        formatv("/{0}t{1}memdef{2}", ProcessPID, getCurrentTID(), MemVal.Index);
+        formatv("/{0}t{1}memdef{2}", ProcessPID, get_threadid(), MemVal.Index);
     SharedMemoryNames.push_back(SharedMemoryName);
     int SharedMemoryFD =
         shm_open(SharedMemoryName.c_str(), O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
@@ -93,7 +87,7 @@ Error SubprocessMemory::addMemoryDefinition(
 
 Expected<int> SubprocessMemory::setupAuxiliaryMemoryInSubprocess(
     std::unordered_map<std::string, MemoryValue> MemoryDefinitions,
-    pid_t ParentPID, long ParentTID, int CounterFileDescriptor) {
+    pid_t ParentPID, uint64_t ParentTID, int CounterFileDescriptor) {
   std::string AuxiliaryMemoryName =
       formatv("/{0}auxmem{1}", ParentTID, ParentPID);
   int AuxiliaryMemoryFileDescriptor =
@@ -145,7 +139,7 @@ Error SubprocessMemory::addMemoryDefinition(
 
 Expected<int> SubprocessMemory::setupAuxiliaryMemoryInSubprocess(
     std::unordered_map<std::string, MemoryValue> MemoryDefinitions,
-    pid_t ParentPID, long ParentTID, int CounterFileDescriptor) {
+    pid_t ParentPID, uint64_t ParentTID, int CounterFileDescriptor) {
   return make_error<Failure>(
       "setupAuxiliaryMemoryInSubprocess is only supported on Linux");
 }

llvm/tools/llvm-exegesis/lib/SubprocessMemory.h

@@ -35,9 +35,6 @@ class SubprocessMemory {
   static constexpr const size_t AuxiliaryMemoryOffset = 1;
   static constexpr const size_t AuxiliaryMemorySize = 4096;
 
-  // Gets the thread ID for the calling thread.
-  static long getCurrentTID();
-
   Error initializeSubprocessMemory(pid_t ProcessID);
 
   // The following function sets up memory definitions. It creates shared
@@ -57,7 +54,7 @@ class SubprocessMemory {
   // section.
   static Expected<int> setupAuxiliaryMemoryInSubprocess(
       std::unordered_map<std::string, MemoryValue> MemoryDefinitions,
-      pid_t ParentPID, long ParentTID, int CounterFileDescriptor);
+      pid_t ParentPID, uint64_t ParentTID, int CounterFileDescriptor);
 
   ~SubprocessMemory();