From 1a756f637fc4276c0d9a279e0e7be89c8e69a2d7 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Fri, 24 Jul 2020 22:09:19 -0700
Subject: [PATCH] ircd::spirit: Isolate aggressive inlining; remove unit-level
 setting.

---
 configure.ac          | 10 ----------
 include/ircd/spirit.h | 16 +++++++++++++---
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/configure.ac b/configure.ac
index 6f40f0a43..9b973be82 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2370,16 +2370,6 @@ SPIRIT_UNIT_CPPFLAGS+=" -include ircd/spirit.h"
 
 AC_SUBST(SPIRIT_UNIT_CXXFLAGS)
 
-dnl Slightly more aggressive than the default of 250. A large number of
-dnl internal functions are generated out of some grammars at the default.
-dnl The more aggressive value embeds rules together for optimization but
-dnl may generate slightly larger functions.
-AM_COND_IF([CLANG],
-[
-	SPIRIT_UNIT_CXXFLAGS+=" -mllvm -inlinehint-threshold=1000"
-	SPIRIT_UNIT_CXXFLAGS+=" -mllvm -inline-threshold=400"
-])
-
 AM_COND_IF([GCC],
 [
 	SPIRIT_UNIT_CXXFLAGS+=" -fno-var-tracking"
diff --git a/include/ircd/spirit.h b/include/ircd/spirit.h
index ac5ce9028..542009448 100644
--- a/include/ircd/spirit.h
+++ b/include/ircd/spirit.h
@@ -26,12 +26,19 @@
 // some false asserts around boolean character tests in spirit.
 #define BOOST_DISABLE_ASSERTS
 
-#pragma GCC visibility push(default)
+// This prevents spirit grammar rules from generating a very large and/or deep
+// call-graph where rules compose together using wrapped indirect calls through
+// boost::function -- this is higly inefficient as the grammar's logic ends up
+// being a fraction of the generated code and the rest is invocation related
+// overhead. By force-flattening here we can allow each entry-point into
+// spirit to compose rules at once and eliminate the wrapping complex.
+#pragma clang attribute push ([[gnu::always_inline]], apply_to = function)
+#pragma clang attribute push ([[gnu::flatten]], apply_to = function)
+
 #include <boost/config.hpp>
 #include <boost/function.hpp>
-#pragma GCC visibility pop
 
-#pragma GCC visibility push(hidden)
+#pragma GCC visibility push (internal)
 #include <boost/fusion/sequence.hpp>
 #include <boost/fusion/iterator.hpp>
 #include <boost/fusion/adapted.hpp>
@@ -45,6 +52,9 @@
 #include <boost/spirit/repository/include/qi_subrule.hpp>
 #pragma GCC visibility pop
 
+#pragma clang attribute pop
+#pragma clang attribute pop
+
 namespace ircd {
 namespace spirit
 __attribute__((visibility("default")))