On 10/28/16 16:05, Bernd Edlinger wrote:
> On 10/27/16 22:23, Joseph Myers wrote:
>> On Thu, 27 Oct 2016, Bernd Edlinger wrote:
>>
>>> Hi,
>>>
>>> by code reading I became aware that libgcc can call count_leading_zeros
>>> in certain cases which can give undefined results. This happens on
>>> signed int128 -> float or double conversions, when the int128 is in
>>> the range
>>> INT64_MAX+1 to UINT64_MAX.
>>
>> I'd expect testcases added to the testsuite that exercise this case at
>> runtime, if not already present.
>>
>
> Yes, thanks. I somehow expected there were already test cases,
> somewhere, but now when you ask that, I begin to doubt as well...
>
> I will try to add an asm("int 3") and see if that gets hit at all.
>
The breakpoint got hit only once, in the libgo testsuite: runtime/pprof.
I see there are some int to float conversion tests at
gcc.dg/torture/fp-int-convert*.c, where it is easy to add a
test case that hits the breakpoint too.
However the test case does not fail before the patch,
it is just slightly undefined behavior, that is not
causing problems (at least for x86_64).
Find attached a new patch with test case.
Boot-strapped on x86_64-pc-linux-gnu.
Is it OK for trunk?
Thanks
Bernd.
2016-10-27 Bernd Edlinger <bernd.edlin...@hotmail.de>
PR libgcc/78067
* libgcc2.c (__floatdisf, __floatdidf): Avoid undefined results from
count_leading_zeros.
testsuite:
2016-10-27 Bernd Edlinger <bernd.edlin...@hotmail.de>
PR libgcc/78067
* gcc.dg/torture/fp-int-convert.h: Add more conversion tests.
Index: libgcc2.c
===================================================================
--- libgcc2.c (revision 241400)
+++ libgcc2.c (working copy)
@@ -1643,6 +1643,11 @@
hi = -(UWtype) hi;
UWtype count, shift;
+#if !defined (COUNT_LEADING_ZEROS_0) || COUNT_LEADING_ZEROS_0 != W_TYPE_SIZE
+ if (hi == 0)
+ count = W_TYPE_SIZE;
+ else
+#endif
count_leading_zeros (count, hi);
/* No leading bits means u == minimum. */
Index: gcc/testsuite/gcc.dg/torture/fp-int-convert.h
===================================================================
--- gcc/testsuite/gcc.dg/torture/fp-int-convert.h (revision 241647)
+++ gcc/testsuite/gcc.dg/torture/fp-int-convert.h (working copy)
@@ -53,6 +53,8 @@ do { \
TEST_I_F_VAL (U, F, HVAL1U (P, U), P_OK (P, U)); \
TEST_I_F_VAL (U, F, HVAL1U (P, U) + 1, P_OK (P, U)); \
TEST_I_F_VAL (U, F, HVAL1U (P, U) - 1, P_OK (P, U)); \
+ TEST_I_F_VAL (I, F, WVAL0S (I), 1); \
+ TEST_I_F_VAL (I, F, -WVAL0S (I), 1); \
} while (0)
#define P_OK(P, T) ((P) >= sizeof(T) * CHAR_BIT)
@@ -74,6 +76,7 @@ do { \
? (S)1 \
: (((S)1 << (sizeof(S) * CHAR_BIT - 2)) \
+ ((S)3 << (sizeof(S) * CHAR_BIT - 2 - P))))
+#define WVAL0S(S) (S)((S)1 << (sizeof(S) * CHAR_BIT / 2 - 1))
#define TEST_I_F_VAL(IT, FT, VAL, PREC_OK) \
do { \
