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@redhat.com>
---
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
--
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