Make /fastlink builds as optimized as non-/fastlink builds

build/config/win/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/clang/clang.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/win/visual_studio_version.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ skipping 68 matching lines @@
         # cmd.exe doesn't understand ANSI escape codes by default,
         # so only enable them if something emulating them is around.
         "-fansi-escape-codes",
       ]
     }
 
     # Clang runtime libraries, such as the sanitizer runtimes, live here.
     lib_dirs = [ "$clang_base_path/lib/clang/$clang_version/lib/windows" ]
   }
 
-  # Ensures that the PDB file contains FIXUP information (growing the PDB file
-  # by about 5%) but does not otherwise alter the output binary. This
+  # /PROFILE ensures that the PDB file contains FIXUP information (growing the
+  # PDB file by about 5%) but does not otherwise alter the output binary. This
   # information is used by the Syzygy optimization tool when decomposing the
   # release image. It is enabled for syzyasan builds and opportunistically for
   # other builds where it is not prohibited (not supported when incrementally
   # linking, using /debug:fastlink, or building with clang).
-  if (is_syzyasan ||
-      (!is_debug && !is_component_build && !is_win_fastlink && !is_clang)) {
+  if (is_syzyasan) {
+    assert(!is_win_fastlink)
     ldflags = [ "/PROFILE" ]
+  } else {
+    if (!is_debug && !is_component_build && !is_clang) {
+      if (is_win_fastlink) {
+        # /PROFILE implies the following linker flags. Therefore if we are
+        # skipping /PROFILE because it is incompatible with /DEBUG:FASTLINK
+        # we should explicitly add these flags in order to avoid unintended
+        # consequences such as larger binaries.
+        ldflags = [
+          "/OPT:REF",
+          "/OPT:ICF",
+          "/INCREMENTAL:NO",
+          "/FIXED:NO",
+        ]
+      } else {
+        ldflags = [ "/PROFILE" ]
+      }
+    }
   }
 
   # arflags apply only to static_libraries. The normal linker configs are only
   # set for executable and shared library targets so arflags must be set
   # elsewhere. Since this is relatively contained, we just apply them in this
   # more general config and they will only have an effect on static libraries.
   arflags = [
     # "No public symbols found; archive member will be inaccessible." This
     # means that one or more object files in the library can never be
     # pulled in to targets that link to this library. It's just a warning that
@@ skipping 298 matching lines @@
 
 # Internal stuff --------------------------------------------------------------
 
 # Config used by the MIDL template to disable warnings.
 config("midl_warnings") {
   if (is_clang) {
     # MIDL generates code like "#endif !_MIDL_USE_GUIDDEF_".
     cflags = [ "-Wno-extra-tokens" ]
   }
 }