[test][PGO] Add a multi-threaded test for continuous PGO.

Author: Wael Yehia

compiler-rt/test/profile/ContinuousSyncMode/multi-threaded.cpp

@@ -0,0 +1,29 @@
+// REQUIRES: target={{.*(darwin|aix).*}}
+
+// RUN: rm -f %t.profraw
+// RUN: %clangxx_pgogen_cont -lpthread %s -o %t.exe -mllvm -disable-vp -fprofile-update=atomic
+// RUN: env LLVM_PROFILE_FILE="%c%t.profraw" %run %t.exe
+// RUN: llvm-profdata show --counts --function=accum  %t.profraw | FileCheck %s
+// CHECK:    Block counts: [100000, 4]
+
+#include <thread>
+
+int x = 0;
+void accum(int n) {
+  for (int i = 0; i < n; i++)
+    x += i; // don't care about accuracy, no need for atomic.
+}
+
+int main() {
+  int init_value = 10000;
+  auto t1 = std::thread(accum, 1*init_value);
+  auto t2 = std::thread(accum, 2*init_value);
+  auto t3 = std::thread(accum, 3*init_value);
+  auto t4 = std::thread(accum, 4*init_value);
+
+  t1.join();
+  t2.join();
+  t3.join();
+  t4.join();
+  return !x;
+}

compiler-rt/test/profile/lit.cfg.py

@@ -138,6 +138,14 @@ def exclude_unsupported_files_for_aix(dirname):
 config.substitutions.append(
     ("%clangxx_pgogen=", build_invocation(clang_cxxflags) + " -fprofile-generate=")
 )
+config.substitutions.append(
+    (
+        "%clangxx_pgogen_cont ",
+        build_invocation(clang_cxxflags)
+        + " -fprofile-generate "
+        + ("-mllvm -runtime-counter-relocation " if runtime_reloc else ""),
+    )
+)
 
 config.substitutions.append(
     ("%clang_cspgogen ", build_invocation(clang_cflags) + " -fcs-profile-generate ")