Enable incremental linking in release component builds

Component builds are, by definition, not optimized for maximum
performance. So incremental linking - which trades a little bit of
performance for much faster build times - is appropriate in release
component builds, as well as in debug builds.

This change enables incremental linking in release component builds.
This also requires turning off /OPT:ICF and /PROFILE in component
builds because they are incompatible with /incremental, but they are
performance related flags so they are also not important for component
builds.

blink_core.dll cannot be incrementally linked in debug x64 component
builds, but it *can* be incrementally linked in release x64 component
builds (and debug/release x86 component builds), and this change
enables incremental linking of blink_core.dll in all supported
configurations.

This drops the chrome rebuild time after touching
third_party\WebKit\Source\core\html\AutoplayExperimentHelper.cpp from
~260 seconds to 9 seconds. The chrome rebuild time after touching
base\win\registry.cc drops from ~200 seconds to less than 2 seconds,
with 21 of 24 link steps skipped entirely.

This also fixes some /INCREMENTAL /OPT:ICF mismatch warnings.

BUG=608801,621236

Review-Url: https://codereview.chromium.org/2331373006
Cr-Commit-Position: refs/heads/master@{#418660}

build/config/compiler/BUILD.gn

@@ -1223,7 +1223,10 @@ if (is_win) {
       "/Gw",
     ]
   }
-  common_optimize_on_ldflags = [ "/OPT:ICF" ]  # Redundant COMDAT folding.
+  common_optimize_on_ldflags = []
+  if (!is_component_build) {
+    common_optimize_on_ldflags += [ "/OPT:ICF" ]  # Redundant COMDAT folding.
+  }
   if (is_official_build) {
     common_optimize_on_ldflags += [
       "/OPT:REF",  # Remove unreferenced data.

build/config/win/BUILD.gn

@@ -101,8 +101,11 @@ config("compiler") {
   # 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.
-  if (!is_debug && !is_win_fastlink && !is_clang) {
+  # 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)) {
     ldflags = [ "/PROFILE" ]
   }
 
@@ -312,8 +315,9 @@ config("windowed") {
 incremental_linking_on_switch = [ "/INCREMENTAL" ]
 incremental_linking_off_switch = [ "/INCREMENTAL:NO" ]
 
-# Disable incremental linking for syzyasan
-if (is_debug && !is_syzyasan) {
+# Disable incremental linking for syzyasan, enable for debug builds and all
+# component builds - any builds where performance is not job one.
+if ((is_debug || is_component_build) && !is_syzyasan) {
   default_incremental_linking_switch = incremental_linking_on_switch
 } else {
   default_incremental_linking_switch = incremental_linking_off_switch

third_party/WebKit/Source/core/BUILD.gn

@@ -180,8 +180,10 @@ component("core") {
   if (is_win && is_debug && is_component_build && current_cpu == "x64") {
     # Incremental linking doesn't work on this target in debug mode for
     # 64-bit builds - the .ilk file gets too large and the incremental
-    # link silently fails. Therefore 32-bit builds should be used for
-    # fastest incremental build performance.
+    # link silently fails. Therefore 32-bit builds or 64-bit release builds
+    # (component either way) should be used for fastest incremental build
+    # performance. VC++ bug filed for 64-bit debug incremental link failures:
+    # https://connect.microsoft.com/VisualStudio/feedback/details/2846790
     configs -= [ "//build/config/win:default_incremental_linking" ]
     configs += [ "//build/config/win:no_incremental_linking" ]
   }