diff --git a/llvm/utils/gn/build/BUILD.gn b/llvm/utils/gn/build/BUILD.gn
--- a/llvm/utils/gn/build/BUILD.gn
+++ b/llvm/utils/gn/build/BUILD.gn
@@ -24,6 +24,9 @@
 
   # The version of host gcc. Ignored if is_clang is true.
   gcc_version = 9
+
+  propellor_phase = 0
+  propellor_profile_dir = ""
 }
 
 assert(!llvm_build_instrumented_coverage || is_clang,
@@ -45,6 +48,23 @@
   cflags_cc = []
   ldflags = target_flags + target_ldflags
 
+  if (propellor_phase == 1) {
+    cflags += [
+      "-funique-internal-linkage-names",
+      "-fbasic-block-sections=labels",
+    ]
+  } else if (propellor_phase == 2) {
+    assert(propellor_profile_dir != "", "")
+    cflags += [
+      "-funique-internal-linkage-names",
+      "-fbasic-block-sections=list=" + propellor_profile_dir + "/cluster.txt",
+    ]
+    ldflags += [
+      "-Wl,--symbol-ordering-file=" + propellor_profile_dir + "/symorder.txt",
+      "-Wl,--no-warn-symbol-ordering",
+    ]
+  }
+
   # Mostly for compiler-rt, see compiler-rt/cmake/config-ix.cmake
   if (current_os == "ios") {
     asmflags += [ "-miphoneos-version-min=8.0" ]