build: add lto configure option

configure.ac

@@ -205,6 +205,12 @@ AC_ARG_ENABLE([werror],
     [enable_werror=$enableval],
     [enable_werror=no])
 
+AC_ARG_ENABLE([lto],
+    [AS_HELP_STRING([--enable-lto],
+                    [enable link-time-optimization (default is no)])],
+    [enable_lto=$enableval],
+    [enable_lto=no])
+
 AC_LANG_PUSH([C++])
 AX_CHECK_COMPILE_FLAG([-Werror],[CXXFLAG_WERROR="-Werror"],[CXXFLAG_WERROR=""])
 
@@ -219,6 +225,12 @@ if test "x$enable_debug" = xyes; then
     fi
 fi
 
+if test "x$enable_lto" = "xyes"; then
+  AX_CHECK_COMPILE_FLAG([-flto],[LTO_CXXFLAGS="$LTO_CXXFLAGS -flto"],[AC_MSG_ERROR(compile failed with -flto)],[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([$LTO_CXXFLAGS -fno-fat-lto-objects],[LTO_CXXFLAGS="$LTO_CXXFLAGS -fno-fat-lto-objects"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_LINK_FLAG([-flto],[LTO_LDFLAGS="$LTO_LDFLAGS -flto"],[AC_MSG_ERROR(link failed with -flto)],[[$CXXFLAG_WERROR]])
+fi
+
 ERROR_CXXFLAGS=
 if test "x$enable_werror" = "xyes"; then
   if test "x$CXXFLAG_WERROR" = "x"; then
@@ -1159,6 +1171,8 @@ AC_SUBST(BITCOIN_CLI_NAME)
 AC_SUBST(BITCOIN_TX_NAME)
 
 AC_SUBST(RELDFLAGS)
+AC_SUBST(LTO_CXXFLAGS)
+AC_SUBST(LTO_LDFLAGS)
 AC_SUBST(ERROR_CXXFLAGS)
 AC_SUBST(HARDENED_CXXFLAGS)
 AC_SUBST(HARDENED_CPPFLAGS)

src/Makefile.am

@@ -4,8 +4,8 @@
 
 DIST_SUBDIRS = secp256k1 univalue
 
-AM_LDFLAGS = $(PTHREAD_CFLAGS) $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS)
-AM_CXXFLAGS = $(HARDENED_CXXFLAGS) $(ERROR_CXXFLAGS)
+AM_LDFLAGS = $(PTHREAD_CFLAGS) $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS) $(LTO_LDFLAGS)
+AM_CXXFLAGS = $(HARDENED_CXXFLAGS) $(ERROR_CXXFLAGS) $(LTO_CXXFLAGS)
 AM_CPPFLAGS = $(HARDENED_CPPFLAGS)
 EXTRA_LIBRARIES =
 

src/util.cpp

@@ -548,16 +548,16 @@ fs::path GetDefaultDataDir()
 #endif
 }
 
-static fs::path pathCached;
-static fs::path pathCachedNetSpecific;
+static fs::path::string_type pathCached;
+static fs::path::string_type pathCachedNetSpecific;
 static CCriticalSection csPathCached;
 
-const fs::path &GetDataDir(bool fNetSpecific)
+fs::path GetDataDir(bool fNetSpecific)
 {
 
     LOCK(csPathCached);
 
-    fs::path &path = fNetSpecific ? pathCachedNetSpecific : pathCached;
+    fs::path path = fNetSpecific ? pathCachedNetSpecific : pathCached;
 
     // This can be called during exceptions by LogPrintf(), so we cache the
     // value so we don't have to do memory allocations after that.
@@ -585,8 +585,8 @@ void ClearDatadirCache()
 {
     LOCK(csPathCached);
 
-    pathCached = fs::path();
-    pathCachedNetSpecific = fs::path();
+    pathCached = fs::path().native();
+    pathCachedNetSpecific = fs::path().native();
 }
 
 fs::path GetConfigFile(const std::string& confPath)

src/util.h

@@ -169,7 +169,7 @@ void AllocateFileRange(FILE *file, unsigned int offset, unsigned int length);
 bool RenameOver(fs::path src, fs::path dest);
 bool TryCreateDirectories(const fs::path& p);
 fs::path GetDefaultDataDir();
-const fs::path &GetDataDir(bool fNetSpecific = true);
+fs::path GetDataDir(bool fNetSpecific = true);
 void ClearDatadirCache();
 fs::path GetConfigFile(const std::string& confPath);
 #ifndef WIN32