Few fixes for PGO on Linux

- Disable AFDO when using PGO
- Don't try to use PGO on NaCl.

Bug: 1107531
Change-Id: Ia2b161834c6467b648513c49527d881df79c9af2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2308170Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790479}

build/config/compiler/BUILD.gn

@@ -86,8 +86,9 @@ declare_args() {
   # We currently only have default profiles for Chromium in-tree, so we disable
   # this by default for all downstream projects, since these profiles are likely
   # nonsensical for said projects.
-  clang_use_default_sample_profile = build_with_chromium && is_official_build &&
-                                     (is_android || is_desktop_linux)
+  clang_use_default_sample_profile =
+      chrome_pgo_phase == 0 && build_with_chromium && is_official_build &&
+      (is_android || is_desktop_linux)
 
   # This configuration is used to select a default profile in Chrome OS based on
   # the microarchitectures we are using. This is only used if
@@ -2195,6 +2196,7 @@ config("afdo") {
       }
     }
     if (_clang_sample_profile != "") {
+      assert(chrome_pgo_phase == 0, "AFDO can't be used in PGO builds")
       rebased_clang_sample_profile =
           rebase_path(_clang_sample_profile, root_build_dir)
       cflags += [ "-fprofile-sample-use=${rebased_clang_sample_profile}" ]

chrome/test/data/nacl/BUILD.gn

@@ -510,6 +510,9 @@ if (is_linux && is_clang) {
     configs -= [ "//build/config/sanitizers:default_sanitizer_flags" ]
     configs -= [ "//build/config/coverage:default_coverage" ]
 
+    # Do not use PGO as it also requires a few symbols.
+    configs -= [ "//build/config/compiler/pgo:default_pgo_flags" ]
+
     # Disable default_init_stack_vars because it inserts memset() calls, but
     # memset() is not available in this libc-free context.
     configs -= [ "//build/config/compiler:default_init_stack_vars" ]