Hi!
As can be seen on the testcases below, on > 64 bit precision bitfields
we either ICE or miscompile.
get_int_cst_ext_nunits already has code that for unsigned precision
in multiplies of HOST_BITS_PER_WIDE_INT it forces TREE_INT_CST_EXT_NUNITS
to be bigger than TREE_INT_CST_NUNITS, the former holds the actual
value (as negative) and is followed by 0 or more -1 values and a final 0
value. But for some reason this isn't done for > HOST_BITS_PER_WIDE_INT
precisions that aren't multiples of HOST_BITS_PER_WIDE_INT, while we want to
say even in those cases that the value is actually not negative, but very
large.
The following patch attempts to do that, by handling those precisions
the same, TREE_INT_CST_NUNITS again hold the negative value, followed by
0 or more -1 values and finally one which is the -1 zero extended to the
precision % HOST_BITS_PER_WIDE_INT (so for the former special case
of precision % HOST_BITS_PER_WIDE_INT == 0 still 0 as before).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
BTW, the tree-pretty-print.c printing of such INTEGER_CSTs still looks
wrong, we use for the unsigned wi::neg_p values
print_hex (const wide_int_ref &, char *) which prints digits rounded up
to BLOCKS_NEEDED (wi.get_precision ()). I think it would be better
to print in that case just the non-padded number of digits (and for digits
not divisible by 4 start with 0x1, 0x3 or 0x7), but not sure if additional
parameter should be added for this to print_hex, or just tree-pretty-print
should call sprintf directly in that case. Preferences?
2015-12-16 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/68835
* tree.c (get_int_cst_ext_nunits): Return
cst.get_precision () / HOST_BITS_PER_WIDE_INT + 1
for all unsigned wi::neg_p (cst) constants.
(build_new_int_cst): If cst.get_precision is not a multiple
of HOST_BITS_PER_WIDE_INT, zero extend -1 to the precision
% HOST_BITS_PER_WIDE_INT.
* gcc.dg/pr68835-1.c: New test.
* gcc.dg/pr68835-2.c: New test.
--- gcc/tree.c.jj 2015-12-16 09:02:11.000000000 +0100
+++ gcc/tree.c 2015-12-16 17:50:25.000000000 +0100
@@ -1245,11 +1245,9 @@ static unsigned int
get_int_cst_ext_nunits (tree type, const wide_int &cst)
{
gcc_checking_assert (cst.get_precision () == TYPE_PRECISION (type));
- /* We need an extra zero HWI if CST is an unsigned integer with its
- upper bit set, and if CST occupies a whole number of HWIs. */
- if (TYPE_UNSIGNED (type)
- && wi::neg_p (cst)
- && (cst.get_precision () % HOST_BITS_PER_WIDE_INT) == 0)
+ /* We need extra HWIs if CST is an unsigned integer with its
+ upper bit set. */
+ if (TYPE_UNSIGNED (type) && wi::neg_p (cst))
return cst.get_precision () / HOST_BITS_PER_WIDE_INT + 1;
return cst.get_len ();
}
@@ -1266,7 +1264,8 @@ build_new_int_cst (tree type, const wide
if (len < ext_len)
{
--ext_len;
- TREE_INT_CST_ELT (nt, ext_len) = 0;
+ TREE_INT_CST_ELT (nt, ext_len)
+ = zext_hwi (-1, cst.get_precision () % HOST_BITS_PER_WIDE_INT);
for (unsigned int i = len; i < ext_len; ++i)
TREE_INT_CST_ELT (nt, i) = -1;
}
--- gcc/testsuite/gcc.dg/pr68835-1.c.jj 2015-12-16 18:14:08.960943653 +0100
+++ gcc/testsuite/gcc.dg/pr68835-1.c 2015-12-16 18:15:56.803447877 +0100
@@ -0,0 +1,12 @@
+/* PR tree-optimization/68835 */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2" } */
+
+unsigned __int128
+foo (unsigned long a, unsigned long b)
+{
+ unsigned __int128 x = (unsigned __int128) a * b;
+ struct { unsigned __int128 a : 96; } w;
+ w.a = x;
+ return w.a;
+}
--- gcc/testsuite/gcc.dg/pr68835-2.c.jj 2015-12-16 18:41:32.162177493 +0100
+++ gcc/testsuite/gcc.dg/pr68835-2.c 2015-12-16 18:43:07.829853729 +0100
@@ -0,0 +1,23 @@
+/* PR tree-optimization/68835 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O2" } */
+
+__attribute__((noinline, noclone)) unsigned __int128
+foo (void)
+{
+ unsigned __int128 x = (unsigned __int128) 0xffffffffffffffffULL;
+ struct { unsigned __int128 a : 65; } w;
+ w.a = x;
+ w.a += x;
+ return w.a;
+}
+
+int
+main ()
+{
+ unsigned __int128 x = foo ();
+ if ((unsigned long long) x != 0xfffffffffffffffeULL
+ || (unsigned long long) (x >> 64) != 1)
+ __builtin_abort ();
+ return 0;
+}
Jakub
