use PCH for clang plugin source too, if enabled

This currently supports only building with Clang on Linux, as
I'm lazy to handle the other cases (and Clang should be usually
self-built anyway). The main compile time cost is in optimizing
the code, but this still saves few seconds per source.

Change-Id: Ib6c0fd874820af737ee1257cb5234fb78bc63ad8
Reviewed-on: https://gerrit.libreoffice.org/80810
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

compilerplugins/.gitignore

@@ -1,6 +1,8 @@
 /clang/clang-timestamp
 /clang/plugin.dll
 /clang/plugin.so
+/clang/clang.pch
+/clang/clang.pch.d
 /clang/sharedvisitor/*.plugininfo
 /clang/sharedvisitor/analyzer
 /clang/sharedvisitor/analyzer.d

compilerplugins/Makefile-clang.mk

@@ -43,6 +43,10 @@ ifeq ($(OS),WNT)
 LO_CLANG_SHARED_PLUGINS=
 endif
 
+# Whether to use precompiled headers for the sources. This is actually controlled
+# by gb_ENABLE_PCH like everywhere else, but unsetting this disables PCH.
+LO_CLANG_USE_PCH=1
+
 # Whether to use precompiled headers for the analyzer too. Does not apply to compiling sources.
 LO_CLANG_USE_ANALYZER_PCH=1
 
@@ -100,6 +104,20 @@ CLANGWERROR := -Werror
 endif
 endif
 
+ifneq ($(LO_CLANG_USE_PCH),)
+# Reset and enable only if actually supported and enabled.
+LO_CLANG_USE_PCH=
+ifneq ($(gb_ENABLE_PCH),)
+ifneq ($(OS),WNT)
+# Currently only Clang PCH is supported (which should usually be the case, as Clang is usually self-built).
+ifneq ($(findstring clang,$(COMPILER_PLUGINS_CXX)),)
+LO_CLANG_USE_PCH=1
+endif
+endif
+endif
+endif
+
+
 compilerplugins: compilerplugins-build
 
 ifdef LO_CLANG_SHARED_PLUGINS
@@ -139,6 +157,7 @@ compilerplugins-clean:
         $(CLANGOBJDIR) \
         $(CLANGOUTDIR)/clang-timestamp \
         $(CLANGOUTDIR)/plugin$(CLANG_DL_EXT) \
+        $(CLANGOUTDIR)/clang.pch{,.d} \
         $(CLANGOUTDIR)/sharedvisitor/*.plugininfo \
         $(CLANGOUTDIR)/sharedvisitor/clang.pch{,.d} \
         $(CLANGOUTDIR)/sharedvisitor/sharedvisitor.{cxx,d,o} \
@@ -176,10 +195,12 @@ else
 
 # clangbuildsrc cxxfile ofile dfile
 define clangbuildsrc
-$(2): $(1) $(SRCDIR)/compilerplugins/Makefile-clang.mk $(CLANGOUTDIR)/clang-timestamp
+$(2): $(1) $(SRCDIR)/compilerplugins/Makefile-clang.mk $(CLANGOUTDIR)/clang-timestamp \
+        $(if $(LO_CLANG_USE_PCH),$(CLANGOUTDIR)/clang.pch)
 	$$(call gb_Output_announce,$(subst $(SRCDIR)/,,$(subst $(BUILDDIR)/,,$(1))),$(true),CXX,3)
 	$(QUIET)$(COMPILER_PLUGINS_CXX) $(CLANGDEFS) $(CLANGCXXFLAGS) $(CLANGWERROR) \
 	$(CLANGINCLUDES) -I$(BUILDDIR)/config_host -I$(CLANGINDIR) $(1) \
+	$(if $(LO_CLANG_USE_PCH),-include-pch $(CLANGOUTDIR)/clang.pch -DPCH_LEVEL=$(gb_ENABLE_PCH)) \
 	-fPIC -c -o $(2) -MMD -MT $(2) -MP -MF $(3)
 
 -include $(3)
@@ -294,7 +315,25 @@ $(CLANGOUTDIR)/sources-shared.txt:
 	touch $@
 endif
 
+ifneq ($(LO_CLANG_USE_PCH),)
+# the PCH for plugin sources themselves
+
+ifeq ($(OS),WNT)
+# TODO
+else
+$(CLANGOUTDIR)/clang.pch: $(CLANGINDIR)/precompiled_clang.hxx \
+        $(SRCDIR)/compilerplugins/Makefile-clang.mk $(CLANGOUTDIR)/clang-timestamp
+	$(call gb_Output_announce,$(subst $(BUILDDIR)/,,$@),$(true),PCH,1)
+	$(QUIET)$(COMPILER_PLUGINS_CXX) -x c++-header $(CLANGDEFS) $(CLANGCXXFLAGS) $(CLANGWERROR) \
+        $(CLANGINCLUDES) -I$(BUILDDIR)/config_host -I$(CLANGINDIR) -DPCH_LEVEL=$(gb_ENABLE_PCH) \
+        -fPIC $< -o $@ -MMD -MT $@ -MP -MF $(CLANGOUTDIR)/clang.pch.d
+endif
+-include $(CLANGOUTDIR)/clang.pch.d
+
+endif
+
 ifdef LO_CLANG_USE_ANALYZER_PCH
+# the PCH for usage in sharedvisitor/analyzer
 
 # these are from the invocation in analyzer.cxx
 LO_CLANG_ANALYZER_PCH_CXXFLAGS := -I$(BUILDDIR)/config_host $(CLANGTOOLDEFS)

compilerplugins/clang/precompiled_clang.hxx

@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * Based on LLVM/Clang.
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ */
+
+// This file is generated manually. Is it based on the output of
+// cat *.cxx *.hxx | grep '#include' | grep 'clang/' | sort -u
+
+#if PCH_LEVEL >= 1
+#include <clang/AST/ASTConsumer.h>
+#include <clang/AST/ASTContext.h>
+#include <clang/AST/Attr.h>
+#include <clang/AST/Comment.h>
+#include <clang/AST/CXXInheritance.h>
+#include <clang/AST/DeclBase.h>
+#include <clang/AST/DeclCXX.h>
+#include <clang/AST/Decl.h>
+#include <clang/AST/DeclTemplate.h>
+#include <clang/AST/ExprCXX.h>
+#include <clang/AST/Expr.h>
+#include <clang/AST/RecursiveASTVisitor.h>
+#include <clang/AST/StmtVisitor.h>
+#include <clang/AST/Type.h>
+#include <clang/Basic/FileManager.h>
+#include <clang/Basic/OperatorKinds.h>
+#include <clang/Basic/SourceManager.h>
+#include <clang/Frontend/CompilerInstance.h>
+#include <clang/Frontend/FrontendAction.h>
+#include <clang/Frontend/FrontendActions.h>
+#include <clang/Frontend/FrontendPluginRegistry.h>
+#include <clang/Lex/Lexer.h>
+#include <clang/Lex/PPCallbacks.h>
+#include <clang/Lex/Preprocessor.h>
+#include <clang/Rewrite/Core/Rewriter.h>
+#include <clang/Sema/SemaDiagnostic.h>
+#include <clang/Sema/Sema.h>
+#include <clang/Sema/SemaInternal.h>
+#include <clang/Tooling/CommonOptionsParser.h>
+#include <clang/Tooling/Refactoring.h>
+#endif
+
+#if PCH_LEVEL >= 2
+// These are included by everything anyway.
+#include "plugin.hxx"
+#include "check.hxx"
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */