add support for Clang's -building-pch-with-obj

This marks the PCH as having an accompanying object file, and
this object file needs to be also built, but this allows the compiler
to skip generating stuff that'd be shared by all the objects using
the PCH. Currently it doesn't make much of a difference, few symbols
if any, but template instantiations could be shared this way, as
soon as Clang gets the necessary support (my WIP patch).

Change-Id: Ib1b86338d85a47b48979558435253dc2672a0da8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87009
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

3 files changed, 26 insertions, 5 deletions

diff --git a/solenv/gbuild/LinkTarget.mk b/solenv/gbuild/LinkTarget.mk
index 0cfa5a25c145..f3fa447a57bf 100644
--- a/solenv/gbuild/LinkTarget.mk
+++ b/solenv/gbuild/LinkTarget.mk
@@ -268,12 +268,14 @@ gb_CxxObject_get_source = $(1)/$(2).cxx
 # compiled with different flags and link that in rather than mixing different
 # flags in one linktarget. If OBJECT_HAS_EXTRA_CXXFLAGS is set, the object
 # has explicitly set additional CXXFLAGS, so in that case avoid using the PCH.
+# T_PCH_EXTRA_CXXFLAGS is used when some object requires extra flags when using
+# the PCH, but they are intended (gb_PrecompiledHeader_pch_with_obj).
 define gb_CxxObject__set_pchflags
 ifneq ($(gb_ENABLE_PCH),)
 ifneq ($(strip $$(PCH_NAME)),)
 ifeq ($(OBJECT_HAS_EXTRA_CXXFLAGS),)
 ifeq ($$(sort $$(PCH_CXXFLAGS) $$(PCH_DEFS)),$$(sort $$(T_CXXFLAGS) $$(T_CXXFLAGS_APPEND) $$(DEFS)))
-$$@ : PCHFLAGS := $$(call gb_PrecompiledHeader_get_enableflags,$$(PCH_NAME),$$(PCH_LINKTARGETMAKEFILENAME))
+$$@ : PCHFLAGS := $$(call gb_PrecompiledHeader_get_enableflags,$$(PCH_NAME),$$(PCH_LINKTARGETMAKEFILENAME)) $$(T_PCH_EXTRA_CXXFLAGS)
 else
 $$(warning No precompiled header available for $$*.cxx .)
 $$(info precompiled header flags : $$(sort $$(PCH_CXXFLAGS) $$(PCH_DEFS)))
@@ -785,6 +787,7 @@ $(call gb_LinkTarget_get_target,$(1)) : PCH_LINKTARGETMAKEFILENAME :=
 $(call gb_LinkTarget_get_target,$(1)) : PCHOBJS :=
 $(call gb_LinkTarget_get_target,$(1)) : PCHOBJEX :=
 $(call gb_LinkTarget_get_target,$(1)) : PCHOBJNOEX :=
+$(call gb_LinkTarget_get_target,$(1)) : T_PCH_EXTRA_CXXFLAGS :=
 $(call gb_LinkTarget_get_target,$(1)) : PE_X86 :=
 $(call gb_LinkTarget_get_target,$(1)) : PDBFILE :=
 $(call gb_LinkTarget_get_target,$(1)) : TARGETGUI :=
@@ -1131,10 +1134,12 @@ $(call gb_CxxObject_get_target,$(2)) : | $(call gb_LinkTarget_get_headers_target
 $(call gb_CxxObject_get_target,$(2)) : T_CXXFLAGS += $(call gb_LinkTarget__get_cxxflags,$(4)) $(3) $(5)
 $(call gb_CxxObject_get_target,$(2)) : OBJECT_HAS_EXTRA_CXXFLAGS := $(if $(strip $(3)),1)
 $(call gb_CxxObject_get_target,$(2)) : \
-	OBJECTOWNER := $(call gb_Object__owner,$(2),$(1))
+	OBJECTOWNER := $(if $(6),,$(call gb_Object__owner,$(2),$(1)))
 ifneq ($(gb_ENABLE_PCH),)
+ifeq ($(6),)
 $(call gb_CxxObject_get_target,$(2)) : $(call gb_LinkTarget_get_pch_timestamp,$(4))
 endif
+endif
 
 ifeq ($(gb_FULLDEPS),$(true))
 $(call gb_LinkTarget_get_dep_target,$(1)) : CXXOBJECTS += $(2)
@@ -1551,6 +1556,11 @@ $(call gb_LinkTarget_get_pch_timestamp,$(4)) : $(call gb_PrecompiledHeader_get_t
 
 $(call gb_LinkTarget__set_precompiled_header_variables,$(1),$(2),$(3),$(4))
 
+ifneq ($(BUILDING_PCH_WITH_OBJ),)
+$(call gb_LinkTarget_add_exception_object,$(1),$(2),,$(4))
+$(call gb_CxxObject_get_target,$(2)) : T_PCH_EXTRA_CXXFLAGS += $(gb_PrecompiledHeader_pch_with_obj)
+endif
+
 ifeq ($(gb_FULLDEPS),$(true))
 -include $(call gb_PrecompiledHeader_get_dep_target,$(3),$(4))
 endif
@@ -1561,7 +1571,7 @@ endef
 define gb_LinkTarget_set_precompiled_header
 ifneq ($(gb_ENABLE_PCH),)
 $(call gb_LinkTarget__set_precompiled_header_impl,$(1),$(2),$(notdir $(2)),$(4))
-$(call gb_PrecompiledHeader_generate_rules,$(notdir $(2)),$(1),$(4))
+$(call gb_PrecompiledHeader_generate_rules,$(notdir $(2)),$(1),$(4),$(2))
 endif
 
 endef
@@ -1581,6 +1591,12 @@ $(call gb_LinkTarget_get_pch_reuse_timestamp,$(4)) : $(call gb_PrecompiledHeader
 	$$(call gb_PrecompiledHeader__copy_reuse_files,$(1),$(3),$(4))
 	mkdir -p $$(dir $$@) && touch $$@
 
+ifneq ($(BUILDING_PCH_WITH_OBJ),)
+# We need to link in also the PCH's object file. Again, rely on a special for_reuse target for dependencies.
+$(if $(wildcard $(call gb_CxxObject_get_source,$(SRCDIR),$(2))),,$(eval $(call gb_Output_error,No such source file $(call gb_CxxObject_get_source,$(SRCDIR),$(2)))))
+$(call gb_LinkTarget_get_target,$(1)) : CXXOBJECTS += $(2)
+endif
+
 endef
 
 
diff --git a/solenv/gbuild/PrecompiledHeaders.mk b/solenv/gbuild/PrecompiledHeaders.mk
index 77c07e65e2a4..1ea64140c50c 100644
--- a/solenv/gbuild/PrecompiledHeaders.mk
+++ b/solenv/gbuild/PrecompiledHeaders.mk
@@ -29,7 +29,7 @@ gb_PrecompiledHeader__get_debugdir = $(if $(call gb_LinkTarget__symbols_enabled,
 # for $(1)'s and things that are constant.
 # The defines are needed to get the right version of gb_PrecompiledHeader__get_debugdir.
 
-# $(call gb_PrecompiledHeader_generate_rules,pchtarget,linktarget,linktargetmakefilename)
+# $(call gb_PrecompiledHeader_generate_rules,pchtarget,linktarget,linktargetmakefilename,pchcxxfile)
 define gb_PrecompiledHeader_generate_rules
 
 $(call gb_PrecompiledHeader_get_dep_target,$(1),$(3)) :
diff --git a/solenv/gbuild/platform/com_GCC_class.mk b/solenv/gbuild/platform/com_GCC_class.mk
index bf15f5e472d0..2ec7a66f3e25 100644
--- a/solenv/gbuild/platform/com_GCC_class.mk
+++ b/solenv/gbuild/platform/com_GCC_class.mk
@@ -88,7 +88,11 @@ gb_PrecompiledHeader_get_enableflags = \
 gb_PrecompiledHeader_EXT := .gch
 endif
 
-# Clang and gcc do not need any extra .o file for PCH
+# Clang supports building extra object file where it puts code that would be shared by all users of the PCH.
+# Unlike with MSVC it is built as a separate step.
+gb_PrecompiledHeader_pch_with_obj = $(BUILDING_PCH_WITH_OBJ)
+
+# This is for MSVC's object file built directly as a side-effect of building the PCH.
 gb_PrecompiledHeader_get_objectfile =
 
 define gb_PrecompiledHeader__command
@@ -105,6 +109,7 @@ $(call gb_Helper_abbreviate_dirs,\
 		$(if $(VISIBILITY),,$(gb_VISIBILITY_FLAGS)) \
 		$(if $(EXTERNAL_CODE),$(gb_CXXFLAGS_Wundef),$(gb_DEFS_INTERNAL)) \
 		$(gb_NO_PCH_TIMESTAMP) \
+		$(gb_PrecompiledHeader_pch_with_obj) \
 		$(6) \
 		$(call gb_cxx_dep_generation_options,$(1),$(call gb_PrecompiledHeader_get_dep_target_tmp,$(2),$(7))) \
 		-c $(patsubst %.cxx,%.hxx,$(3)) \