From aa56d27aead95faedd6225322b7783d1437e1013 Mon Sep 17 00:00:00 2001
From: Dianne Skoll <dianne@skoll.ca>
Date: Mon, 20 Oct 2025 11:32:25 -0400
Subject: [PATCH] Better checking for -flto flags.

---
 configure    | 85 +++++++++++++++++++++++++++++++++++++++-------------
 configure.ac | 44 +++++++++++++++++----------
 2 files changed, 92 insertions(+), 37 deletions(-)

diff --git a/configure b/configure
index ac0af0f4..2ae949bc 100755
--- a/configure
+++ b/configure
@@ -2660,6 +2660,12 @@ cat <<'EOF'
 
 EOF
 
+ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
 ac_config_headers="$ac_config_headers src/config.h"
 
 
@@ -4221,29 +4227,66 @@ fi
 
 
 if test "$GCC" = yes; then
-	CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
+   	CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
         # Check for link-time optimization support
-        f=-flto=auto
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CC supports $f" >&5
-printf %s "checking whether $CC supports $f... " >&6; }
-        if $CC -Werror -E $f - < /dev/null > /dev/null 2>&1 ; then
-            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-            CFLAGS="$CFLAGS $f"
-            f=-ffat-lto-objects
-            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CC supports $f" >&5
-printf %s "checking whether $CC supports $f... " >&6; }
-            if $CC -Werror -E $f - < /dev/null > /dev/null 2>&1 ; then
-                { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-                CFLAGS="$CFLAGS $f"
-            else
-                { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-            fi
+        CFLAGS="$CFLAGS -flto=auto"
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -flto=auto" >&5
+printf %s "checking whether $CC supports -flto=auto... " >&6; }
+        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+int x = 1;
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"
+then :
+  lto=yes
+else case e in #(
+  e) lto=no
+                ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam \
+    conftest$ac_exeext conftest.$ac_ext
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $lto" >&5
+printf "%s\n" "$lto" >&6; }
+        if test "x$lto" != "xyes" ; then
+	    CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
         else
-            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
+            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -ffat-lto-object" >&5
+printf %s "checking whether $CC supports -ffat-lto-object... " >&6; }
+            CFLAGS="$CFLAGS -flto=auto -ffat-lto-objects"
+            cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+int x = 1;
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"
+then :
+  lto=yes
+else case e in #(
+  e) lto=no
+                 ;;
+esac
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam \
+    conftest$ac_exeext conftest.$ac_ext
+            { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $lto" >&5
+printf "%s\n" "$lto" >&6; }
+            if test "x$lto" != "xyes" ; then
+                CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes -flto=auto"
+            fi
         fi
 fi
 
diff --git a/configure.ac b/configure.ac
index 4dbe445f..07d2cc70 100644
--- a/configure.ac
+++ b/configure.ac
@@ -13,6 +13,7 @@ cat <<'EOF'
 
 EOF
 
+AC_LANG([C])
 AC_CONFIG_HEADERS([src/config.h])
 
 AC_ARG_ENABLE(perl-build-artifacts,
@@ -44,24 +45,35 @@ AC_CHECK_HEADERS(strings.h sys/types.h glob.h wctype.h locale.h langinfo.h sys/i
 dnl Checks for typedefs, structures, and compiler characteristics.
 AC_STRUCT_TM
 
-if test "$GCC" = yes; then
-	CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
+if test "$GCC" = yes; then 
+   	CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
         # Check for link-time optimization support
-        f=-flto=auto
-        AC_MSG_CHECKING([whether $CC supports $f])
-        if $CC -Werror -E $f - < /dev/null > /dev/null 2>&1 ; then
-            AC_MSG_RESULT([yes])
-            CFLAGS="$CFLAGS $f"
-            f=-ffat-lto-objects
-            AC_MSG_CHECKING([whether $CC supports $f])
-            if $CC -Werror -E $f - < /dev/null > /dev/null 2>&1 ; then
-                AC_MSG_RESULT([yes])
-                CFLAGS="$CFLAGS $f"
-            else
-                AC_MSG_RESULT([no])
-            fi
+        CFLAGS="$CFLAGS -flto=auto"
+        AC_MSG_CHECKING([whether $CC supports -flto=auto])
+        AC_LINK_IFELSE(
+            [AC_LANG_PROGRAM(
+               [[int x = 1;]],
+               [[]])],
+               [lto=yes],
+               [lto=no]
+               )
+        AC_MSG_RESULT([$lto])
+        if test "x$lto" != "xyes" ; then
+	    CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes"
         else
-            AC_MSG_RESULT([no])
+            AC_MSG_CHECKING([whether $CC supports -ffat-lto-object])
+            CFLAGS="$CFLAGS -flto=auto -ffat-lto-objects"
+            AC_LINK_IFELSE(
+                [AC_LANG_PROGRAM(
+                    [[int x = 1;]],
+                    [[]])],
+                [lto=yes],
+                [lto=no]
+                )
+            AC_MSG_RESULT([$lto])
+            if test "x$lto" != "xyes" ; then
+                CFLAGS="$CFLAGS -Wall -Wextra -Wstrict-prototypes -flto=auto"
+            fi
         fi
 fi