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m4: workaround clang/glibc problem with isnan()

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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.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrange 2017-08-11 17:23:56 +01:00
parent e255cf02b2
commit 1c21dd711c
1 changed files with 18 additions and 0 deletions
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18
m4/virt-compile-warnings.m4
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@ -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"