S390: Do not set FE_INEXACT with feraiseexcept (FE_OWERFLOW|FE_UNDERFLOW).

On s390 feraiseexcept (FE_OVERFLOW|FE_UNDERFLOW) sets FE_INEXACT, too.
This patch uses z196 zarch load rounded instruction which can suppress
FE_INEXACT exception if gcc has z196 support in used configuration.
Otherwise FE_INEXACT flag is set as before. The gcc support is tested
in a new configure-check.

A comment in fsetexcptflg.c is corrected as new exceptions are not
executed with the next floating-point instruction if fpc is set with
_FPU_SETCW macro. It seems the comment was copied e.g. from
sysdeps/x86_64/fpu/fsetexcptflg.c file.

ChangeLog:

	* config.h.in (HAVE_S390_MIN_Z196_ZARCH_ASM_SUPPORT):
	New undefine.
	* sysdeps/s390/configure.ac: Add test for z196 zarch support.
	* sysdeps/s390/configure: Regenerated.
	* sysdeps/s390/fpu/fraiseexcpt.c (__feraiseexcept): Use ledbra
	instruction for raising over-/underflow if z196 zarch is supported
	by default.
	* sysdeps/s390/fpu/fsetexcptflg.c (fesetexceptflag):
	Correct comment.

1 files changed, 26 insertions, 0 deletions

diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
index 1db6d84a20..8a782e7c3a 100644
--- a/sysdeps/s390/configure.ac
+++ b/sysdeps/s390/configure.ac
@@ -86,5 +86,31 @@ then
   AC_DEFINE(HAVE_S390_VX_GCC_SUPPORT)
 fi
 
+AC_CACHE_CHECK(for S390 z196 zarch instruction support as default,
+	       libc_cv_asm_s390_min_z196_zarch, [dnl
+cat > conftest.c <<\EOF
+float testinsn (double e)
+{
+    float d;
+    __asm__ ("ledbra %0,5,%1,4" : "=f" (d) : "f" (e) );
+    return d;
+}
+EOF
+dnl
+dnl test, if assembler supports S390 z196 zarch instructions as default
+if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS --shared conftest.c
+			-o conftest.o &> /dev/null]) ;
+then
+  libc_cv_asm_s390_min_z196_zarch=yes
+else
+  libc_cv_asm_s390_min_z196_zarch=no
+fi
+rm -f conftest* ])
+
+if test "$libc_cv_asm_s390_min_z196_zarch" = yes ;
+then
+  AC_DEFINE(HAVE_S390_MIN_Z196_ZARCH_ASM_SUPPORT)
+fi
+
 test -n "$critic_missing" && AC_MSG_ERROR([
 *** $critic_missing])