From 2799fe4cdbe77e017544f2fe61ae9baef650dbe6 Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Tue, 21 Dec 2021 19:34:40 +0100
Subject: enable LTO in optimized builds
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gives 2-5% performance improvement across a board of tests.
LTO is broken when using clang; some libs link fine while others crash
the linker with a segfault in the llvm linker plugin. 🙁
---
 configure.ac | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 8a01c33ec..a86d88fad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -147,6 +147,20 @@ if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
     LDFLAGS="-latomic $LDFLAGS"
 fi
 
+# LTO is currently broken with clang for unknown reasons; ld segfaults in the llvm plugin
+AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto],[Enable LTO (only supported with GCC) [default=no]]),
+  lto=$enableval, lto=no)
+if test "$lto" = yes; then
+    if $CXX --version | grep -q GCC; then
+        AC_SUBST(CXXLTO, [-flto=jobserver])
+    else
+        echo "error: LTO is only supported with GCC at the moment" >&2
+        exit 1
+    fi
+else
+    AC_SUBST(CXXLTO, [""])
+fi
+
 PKG_PROG_PKG_CONFIG
 
 AC_ARG_ENABLE(shared, AS_HELP_STRING([--enable-shared],[Build shared libraries for Nix [default=yes]]),
-- 
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