Index: utils/perf-training/CMakeLists.txt
===================================================================
--- utils/perf-training/CMakeLists.txt
+++ utils/perf-training/CMakeLists.txt
@@ -30,13 +30,18 @@
   endif()
 
   if(NOT LLVM_PROFDATA)
-    message(FATAL_ERROR "Must set LLVM_PROFDATA to point to llvm-profdata to use for merging PGO data")
+    set(LLVM_PROFDATA ${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-profdata)
+    message(STATUS "LLVM_PROFDATA is set to point to llvm-profdata built from the sources")
+    set(GENERATE_PROFDATA_DEPENDS_ON_LLVM_PROFTDATA TRUE)
   endif()
-
+  
   add_custom_target(generate-profdata
     COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA} ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR}
     COMMENT "Merging profdata"
     DEPENDS generate-profraw)
+  if (GENERATE_PROFDATA_DEPENDS_ON_LLVM_PROFTDATA)
+    add_dependencies(generate-profdata llvm-profdata)
+  endif()
 endif()
 
 find_program(DTRACE dtrace)