When building libvirt with clang we get bogus warnings about 'double' being promoted to 'long double' when calling isnan(). https://bugzilla.redhat.com/show_bug.cgi?id=1472437 Detect this broken isnan() / compiler combination and disable the -Wdouble-promotion flag. Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx> --- m4/virt-compile-warnings.m4 | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4 index fa0940fc6..7b56115ce 100644 --- a/m4/virt-compile-warnings.m4 +++ b/m4/virt-compile-warnings.m4 @@ -134,6 +134,24 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[ [lv_cv_gcc_wlogical_op_equal_expr_broken=yes]) CFLAGS="$save_CFLAGS"]) + AC_CACHE_CHECK([whether clang gives bogus warnings for -Wdouble-promotion], + [lv_cv_clang_double_promotion_broken], [ + save_CFLAGS="$CFLAGS" + CFLAGS="-O2 -Wdouble-promotion -Werror" + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[ + #include <math.h> + ]], [[ + float f = 0.0; + return isnan(f);]])], + [lv_cv_clang_double_promotion_broken=no], + [lv_cv_clang_double_promotion_broken=yes]) + CFLAGS="$save_CFLAGS"]) + + if test "$lv_cv_clang_double_promotion_broken" = "yes"; + then + dontwarn="$dontwarn -Wdouble-promotion" + fi + # We might fundamentally need some of these disabled forever, but # ideally we'd turn many of them on dontwarn="$dontwarn -Wfloat-equal" -- 2.13.3 -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
