use noexceptions .pch only when actually needed

Let's assume that all cxx objects use exceptions by default, unless explicitly
added using add_noexception_cxxobject. This should avoid the need to generate
noexceptions .pch in most cases, as noexceptions cxx objects are currently rare.
It also avoids a bug in MSVC that makes .pch generation fail with error C1033
(e.g. comment from 'Fish Fish' in
https://connect.microsoft.com/VisualStudio/feedback/details/98831/fatal-error-c1033-cannot-open-program-database-debug-vc80-idb).

Change-Id: I31c575a34539d58c42754ecfe6639c5b5e5854f1

2 files changed, 14 insertions, 4 deletions

diff --git a/solenv/gbuild/LinkTarget.mk b/solenv/gbuild/LinkTarget.mk
index 3df81343ee47..6715a2f5bee7 100644
--- a/solenv/gbuild/LinkTarget.mk
+++ b/solenv/gbuild/LinkTarget.mk
@@ -560,6 +560,8 @@ $(call gb_LinkTarget_get_target,$(1)) : LIBRARY_X64 :=
 $(call gb_LinkTarget_get_headers_target,$(1)) \
 $(call gb_LinkTarget_get_target,$(1)) : PCH_NAME :=
 $(call gb_LinkTarget_get_target,$(1)) : PCHOBJS :=
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJEX :=
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJNOEX :=
 $(call gb_LinkTarget_get_headers_target,$(1)) \
 $(call gb_LinkTarget_get_target,$(1)) : PDBFILE :=
 $(call gb_LinkTarget_get_target,$(1)) : EXTRAOBJECTLISTS :=
@@ -876,10 +878,7 @@ $(call gb_CxxObject_get_target,$(2)) : \
 ifeq ($(gb_FULLDEPS),$(true))
 $(call gb_LinkTarget_get_dep_target,$(1)) : CXXOBJECTS += $(2)
 $(call gb_LinkTarget_get_dep_target,$(1)) : $(call gb_CxxObject_get_dep_target,$(2))
-# It is not known by this time (or at least I don't know how to find out) which
-# PCH variant will be used, so depend on both.
 $(call gb_CxxObject_get_target,$(2)) : $(call gb_PrecompiledHeader_get_timestamp,$(1))
-$(call gb_CxxObject_get_target,$(2)) : $(call gb_NoexPrecompiledHeader_get_timestamp,$(1))
 endif
 
 endef
@@ -1016,6 +1015,9 @@ endef
 
 define gb_LinkTarget_add_noexception_object
 $(call gb_LinkTarget_add_cxxobject,$(1),$(2),$(gb_LinkTarget_NOEXCEPTIONFLAGS) $(call gb_LinkTarget__get_cxxflags,$(3)))
+# noexception objects are rare, so generate matching .pch only when needed
+$(call gb_CxxObject_get_target,$(2)) : $(call gb_NoexPrecompiledHeader_get_timestamp,$(1))
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJS = $$(PCHOBJEX) $$(PCHOBJNOEX)
 endef
 
 define gb_LinkTarget_add_exception_object
@@ -1197,7 +1199,9 @@ $(call gb_LinkTarget_get_clean_target,$(1)) : $(call gb_NoexPrecompiledHeader_ge
 $(call gb_NoexPrecompiledHeader_get_target,$(3)) : $(2).cxx
 
 $(call gb_LinkTarget_get_target,$(1)) : PCH_NAME := $(3)
-$(call gb_LinkTarget_get_target,$(1)) : PCHOBJS = $(call gb_PrecompiledHeader_get_target,$(3)).obj $(call gb_NoexPrecompiledHeader_get_target,$(3)).obj
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJEX = $(call gb_PrecompiledHeader_get_target,$(3)).obj
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJNOEX = $(call gb_NoexPrecompiledHeader_get_target,$(3)).obj
+$(call gb_LinkTarget_get_target,$(1)) : PCHOBJS = $$(PCHOBJEX)
 
 $(call gb_LinkTarget_get_headers_target,$(1)) \
 $(call gb_LinkTarget_get_target,$(1)) : DEFS := $$(DEFS) -DPRECOMPILED_HEADERS
diff --git a/solenv/gbuild/platform/com_MSC_class.mk b/solenv/gbuild/platform/com_MSC_class.mk
index 0ce41541e907..04209f999385 100644
--- a/solenv/gbuild/platform/com_MSC_class.mk
+++ b/solenv/gbuild/platform/com_MSC_class.mk
@@ -90,6 +90,12 @@ endef
 
 # PrecompiledHeader class
 
+# Note: MSVC has a race condition when dealing with .pdb files, that can result in error C1033 when
+# the .pdb file already exists and two cl.exe invocations try to modify it at the same time (which
+# is apparently most likely when generating both .pch files). The no-exceptions variant should be
+# rarely needed now, but in case this turns out to be a problem in practice, this will need to
+# be handled somehow (such as order-dependency of one on another).
+
 gb_PrecompiledHeader_get_enableflags = -Yu$(1).hxx \
 	-FI$(1).hxx \
 	-Fp$(call gb_PrecompiledHeader_get_target,$(1))