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authorJoseph Myers <joseph@codesourcery.com>2014-10-09 01:00:41 +0000
committerJoseph Myers <joseph@codesourcery.com>2014-10-09 01:00:41 +0000
commit43059f42dbd6dd3926c33ee0cbc7583f0c3e84b9 (patch)
tree49c139b7c42576c9b0a4fb3b25424761f37ed8c6
parent2d6a47ba4ca899746db7fb5ba75a82f2cda93a91 (diff)
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soft-fp: Make extensions of subnormals from XFmode to TFmode signal underflow if traps enabled.
This patch fixes a soft-fp corner case I previously noted in <https://sourceware.org/ml/libc-alpha/2013-10/msg00349.html>: when trapping on underflow is enabled, extensions of subnormals from XFmode to TFmode need to signal underflow because the result is tiny (but exact, so the underflow flag is not raised unless trapping is enabled). To avoid any excess initialization or tests for other cases of floating-point extensions, a new FP_INIT_TRAPPING_EXCEPTIONS is added that does the initialization required for this particular case (more than FP_INIT_EXCEPTIONS, less than FP_INIT_ROUNDMODE, in general), and FP_NO_EXACT_UNDERFLOW is added to stub out FP_TRAPPING_EXCEPTIONS tests for those cases of extensions where the test would be dead code, to avoid any uninitialized variable warnings. As the relevant case only applies in libgcc, not to any use of soft-fp in glibc, there is no bug report in Bugzilla and no non-default definitions of FP_INIT_TRAPPING_EXCEPTIONS are added by the patch. A testcase will be added to GCC as part of an update of soft-fp in libgcc once this patch is in libc. Tested for powerpc-nofpu that the disassembly of installed shared libraries is unchanged by this patch. Bootstrapped GCC with updated soft-fp with no regressions on x86_64-unknown-linux-gnu and verified that a test of the relevant case passes where it failed before. * soft-fp/op-common.h (FP_EXTEND): When a subnormal input produces a subnormal result, set the underflow exception if trapping on underflow is enabled. * soft-fp/soft-fp.h (FP_INIT_TRAPPING_EXCEPTIONS): New macro. (FP_INIT_EXCEPTIONS): Default to FP_INIT_TRAPPING_EXCEPTIONS. [FP_NO_EXACT_UNDERFLOW] (FP_TRAPPING_EXCEPTIONS): Undefine and redefine to 0. * soft-fp/extenddftf2.c (FP_NO_EXACT_UNDERFLOW): Define. * soft-fp/extendsfdf2.c (FP_NO_EXACT_UNDERFLOW): Likewise. * soft-fp/extendsftf2.c (FP_NO_EXACT_UNDERFLOW): Likewise. * soft-fp/extendxftf2.c (__extendxftf2): Use FP_INIT_TRAPPING_EXCEPTIONS instead of FP_INIT_ROUNDMODE.
-rw-r--r--ChangeLog13
-rw-r--r--soft-fp/extenddftf2.c1
-rw-r--r--soft-fp/extendsfdf2.c1
-rw-r--r--soft-fp/extendsftf2.c1
-rw-r--r--soft-fp/extendxftf2.c2
-rw-r--r--soft-fp/op-common.h2
-rw-r--r--soft-fp/soft-fp.h18
7 files changed, 36 insertions, 2 deletions
diff --git a/ChangeLog b/ChangeLog
index b5faff4fe7c..703934d098a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,18 @@
2014-10-09 Joseph Myers <joseph@codesourcery.com>
+ * soft-fp/op-common.h (FP_EXTEND): When a subnormal input produces
+ a subnormal result, set the underflow exception if trapping on
+ underflow is enabled.
+ * soft-fp/soft-fp.h (FP_INIT_TRAPPING_EXCEPTIONS): New macro.
+ (FP_INIT_EXCEPTIONS): Default to FP_INIT_TRAPPING_EXCEPTIONS.
+ [FP_NO_EXACT_UNDERFLOW] (FP_TRAPPING_EXCEPTIONS): Undefine and
+ redefine to 0.
+ * soft-fp/extenddftf2.c (FP_NO_EXACT_UNDERFLOW): Define.
+ * soft-fp/extendsfdf2.c (FP_NO_EXACT_UNDERFLOW): Likewise.
+ * soft-fp/extendsftf2.c (FP_NO_EXACT_UNDERFLOW): Likewise.
+ * soft-fp/extendxftf2.c (__extendxftf2): Use
+ FP_INIT_TRAPPING_EXCEPTIONS instead of FP_INIT_ROUNDMODE.
+
* soft-fp/soft-fp.h (FP_CLEAR_EXCEPTIONS): Remove macro.
* sysdeps/sparc/sparc32/soft-fp/q_itoq.c: Define FP_NO_EXCEPTIONS.
(_Q_itoq): Do not use FP_DECL_EX, FP_CLEAR_EXCEPTIONS or
diff --git a/soft-fp/extenddftf2.c b/soft-fp/extenddftf2.c
index 6984b41a800..17655326d8f 100644
--- a/soft-fp/extenddftf2.c
+++ b/soft-fp/extenddftf2.c
@@ -28,6 +28,7 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
+#define FP_NO_EXACT_UNDERFLOW
#include "soft-fp.h"
#include "double.h"
#include "quad.h"
diff --git a/soft-fp/extendsfdf2.c b/soft-fp/extendsfdf2.c
index a9b6bfbee78..6224195ce91 100644
--- a/soft-fp/extendsfdf2.c
+++ b/soft-fp/extendsfdf2.c
@@ -28,6 +28,7 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
+#define FP_NO_EXACT_UNDERFLOW
#include "soft-fp.h"
#include "single.h"
#include "double.h"
diff --git a/soft-fp/extendsftf2.c b/soft-fp/extendsftf2.c
index 07fc3679aca..f67d614d7c9 100644
--- a/soft-fp/extendsftf2.c
+++ b/soft-fp/extendsftf2.c
@@ -28,6 +28,7 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
+#define FP_NO_EXACT_UNDERFLOW
#include "soft-fp.h"
#include "single.h"
#include "quad.h"
diff --git a/soft-fp/extendxftf2.c b/soft-fp/extendxftf2.c
index 67b909563f2..a1386a68e65 100644
--- a/soft-fp/extendxftf2.c
+++ b/soft-fp/extendxftf2.c
@@ -39,7 +39,7 @@ __extendxftf2 (XFtype a)
FP_DECL_Q (R);
TFtype r;
- FP_INIT_ROUNDMODE;
+ FP_INIT_TRAPPING_EXCEPTIONS;
FP_UNPACK_RAW_E (A, a);
#if (2 * _FP_W_TYPE_SIZE) < _FP_FRACBITS_Q
FP_EXTEND (Q, E, 4, 4, R, A);
diff --git a/soft-fp/op-common.h b/soft-fp/op-common.h
index ec0bc426e36..e3212ecfd54 100644
--- a/soft-fp/op-common.h
+++ b/soft-fp/op-common.h
@@ -1522,6 +1522,8 @@
_FP_FRAC_SLL_##dwc (D, (_FP_FRACBITS_##dfs \
- _FP_FRACBITS_##sfs)); \
D##_e = 0; \
+ if (FP_TRAPPING_EXCEPTIONS & FP_EX_UNDERFLOW) \
+ FP_SET_EXCEPTION (FP_EX_UNDERFLOW); \
} \
else \
{ \
diff --git a/soft-fp/soft-fp.h b/soft-fp/soft-fp.h
index ead9c978749..4018b0ee914 100644
--- a/soft-fp/soft-fp.h
+++ b/soft-fp/soft-fp.h
@@ -108,9 +108,15 @@
#endif
/* Initialize any machine-specific state used in
+ FP_TRAPPING_EXCEPTIONS or FP_HANDLE_EXCEPTIONS. */
+#ifndef FP_INIT_TRAPPING_EXCEPTIONS
+# define FP_INIT_TRAPPING_EXCEPTIONS FP_INIT_ROUNDMODE
+#endif
+
+/* Initialize any machine-specific state used in
FP_HANDLE_EXCEPTIONS. */
#ifndef FP_INIT_EXCEPTIONS
-# define FP_INIT_EXCEPTIONS FP_INIT_ROUNDMODE
+# define FP_INIT_EXCEPTIONS FP_INIT_TRAPPING_EXCEPTIONS
#endif
#ifndef FP_HANDLE_EXCEPTIONS
@@ -162,6 +168,16 @@
#endif
+/* A file using soft-fp may define FP_NO_EXACT_UNDERFLOW before
+ including soft-fp.h to indicate that, although a macro used there
+ could allow for the case of exact underflow requiring the underflow
+ exception to be raised if traps are enabled, for the particular
+ arguments used in that file no exact underflow can occur. */
+#ifdef FP_NO_EXACT_UNDERFLOW
+# undef FP_TRAPPING_EXCEPTIONS
+# define FP_TRAPPING_EXCEPTIONS 0
+#endif
+
#define _FP_ROUND_NEAREST(wc, X) \
do \
{ \