[test-suite] Add cmake option to use IR PGO (TEST_SUITE_USE_IR_PGO)

This allows building programs in the test suite with LLVM's IR PGO
feature. Support for re-building programs with the collected profdata is
already present.

Differential Revision: https://reviews.llvm.org/D57985

llvm-svn: 353591

Author: vedantk

CMakeLists.txt

@@ -94,6 +94,8 @@ Make sure it is in your path or set TEST_SUITE_COLLECT_CODE_SIZE to OFF")
   endif()
 endif()
 
+option(TEST_SUITE_USE_IR_PGO
+  "Use IR PGO instrumentation (requires TEST_SUITE_PROFILE_GENERATE)" OFF)
 
 # Enable profile generate mode in lit. Note that this does not automatically
 # add something like -fprofile-instr-generate to the compiler flags.
@@ -109,9 +111,15 @@ Make sure it is in your path or set TEST_SUITE_PROFILE_GENERATE to OFF")
   endif()
 
   set(TEST_SUITE_PROFILE_GENERATE "True")
-  list(APPEND CFLAGS -fprofile-instr-generate)
-  list(APPEND CXXFLAGS -fprofile-instr-generate)
-  list(APPEND LDFLAGS -fprofile-instr-generate)
+
+  set(profile_instrumentation_flags -fprofile-instr-generate)
+  if(TEST_SUITE_USE_IR_PGO)
+    set(profile_instrumentation_flags -fprofile-generate)
+  endif()
+
+  list(APPEND CFLAGS   ${profile_instrumentation_flags})
+  list(APPEND CXXFLAGS ${profile_instrumentation_flags})
+  list(APPEND LDFLAGS  ${profile_instrumentation_flags})
 else()
   set(TEST_SUITE_PROFILE_GENERATE "False")
 endif()

litsupport/README.md

@@ -70,7 +70,8 @@ code; typical examples are:
   ssh to run benchmarks on a remote device (assuming shared file systems).
 - `cmake -DTEST_SUITE_PROFILE_GENERATE` compiles benchmark with
   `-fprofile-instr-generate` and enables the `profilegen` module that runs
-  `llvm-profdata` after running the benchmarks.
+  `llvm-profdata` after running the benchmarks. To use LLVM IR PGO instead of
+  the clang frontend's PGO feature, set `-DTEST_SUITE_USE_IR_PGO=On`.
 
 Available modules are found in the `litsupport/modules` directory.