On 10/27/20 1:46 PM, Richard Sandiford wrote:
Jakub Jelinek via Gcc <gcc@gcc.gnu.org> writes:
On Tue, Oct 27, 2020 at 01:18:03PM -0400, Andrew MacLeod via Gcc wrote:
I was looking at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97596
and the ranger is constructing some 128 bit constants and calling
wide_int_to_tree to turn them into trees.
In particular, it starts with the value
p r.lower_bound(0)
{<wide_int_storage> = {val = {-65535, 9223372036854775807, 140737488257608},
len = 2, precision = 128}, static is_sign_extended = true}
p r.lower_bound(0).dump()
[0x7fffffffffffffff,0xffffffffffff0001], precision = 128
 and proceeds to call
wide_int new_lb = wi::set_bit (r.lower_bound (0), 127)
and creates the value:
p new_lb
{<wide_int_storage> = {val = {-65535, -1, 0}, len = 2, precision = 128},
static is_sign_extended = true}
This is non-canonical and so invalid, if the low HWI has the MSB set
and the high HWI is -1, it should have been just
val = {-65535}, len = 1, precision = 128}
I guess the bug is that wi::set_bit_large doesn't call canonize.
Yeah, looks like a micro-optimisation gone wrong.
So perhaps totally untested:
--- gcc/wide-int.cc.jj 2020-10-19 18:42:41.134426398 +0200
+++ gcc/wide-int.cc 2020-10-27 18:33:38.546703763 +0100
@@ -702,8 +702,11 @@ wi::set_bit_large (HOST_WIDE_INT *val, c
/* If the bit we just set is at the msb of the block, make sure
that any higher bits are zeros. */
if (bit + 1 < precision && subbit == HOST_BITS_PER_WIDE_INT - 1)
- val[len++] = 0;
- return len;
+ {
+ val[len++] = 0;
+ return len;
+ }
+ return canonize (val, len, precision);
}
else
{
LGTM, thanks.
Richard
Seems to resolve my problem.
want me to run this thru the tests and apply it to this PR, or is that
already underway? :-)
Andrew
