diff options
| author | Jakub Jelinek <jakub@redhat.com> | 2022-07-01 11:17:41 +0200 |
|---|---|---|
| committer | Jakub Jelinek <jakub@redhat.com> | 2022-07-30 11:34:30 +0200 |
| commit | 527dccb33e54ffe49fb1507fc4539968f48a9d12 (patch) | |
| tree | 245d3cca08c87ca257368df0b0ff2566f55c8fde | |
| parent | 2339ee2c89af80270840e04fc0906acea765489f (diff) | |
wide-int: Fix up wi::shifted_mask [PR106144]
As the following self-test testcase shows, wi::shifted_mask sometimes
doesn't create canonicalized wide_ints, which then fail to compare equal
to canonicalized wide_ints with the same value.
In particular, wi::mask (128, false, 128) gives { -1 } with len 1 and prec 128,
while wi::shifted_mask (0, 128, false, 128) gives { -1, -1 } with len 2
and prec 128.
The problem is that the code is written with the assumption that there are
3 bit blocks (or 2 if start is 0), but doesn't consider the possibility
where there are 2 bit blocks (or 1 if start is 0) where the highest block
isn't present. In that case, there is the optional block of negate ? 0 : -1
elts, followed by just one elt (either one from the if (shift) or just
negate ? -1 : 0) and the rest is implicit sign-extension.
Only if end < prec there is 1 or more bits above it that have different bit
value and so we need to emit all the elts till end and then one more elt.
if (end == prec) would work too, because we have:
if (width > prec - start)
width = prec - start;
unsigned int end = start + width;
so end is guaranteed to be end <= prec, dunno what is preferred.
2022-07-01 Jakub Jelinek <jakub@redhat.com>
PR middle-end/106144
* wide-int.cc (wi::shifted_mask): If end >= prec, return right after
emitting element for shift or if shift is 0 first element after start.
(wide_int_cc_tests): Add tests for equivalency of wi::mask and
wi::shifted_mask with 0 start.
(cherry picked from commit e52592073f6df3d7a3acd9f0436dcc32a8b7493d)
| -rw-r--r-- | gcc/wide-int.cc | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/gcc/wide-int.cc b/gcc/wide-int.cc index f61b9fefc13..1fee0788554 100644 --- a/gcc/wide-int.cc +++ b/gcc/wide-int.cc @@ -842,6 +842,13 @@ wi::shifted_mask (HOST_WIDE_INT *val, unsigned int start, unsigned int width, val[i++] = negate ? block : ~block; } + if (end >= prec) + { + if (!shift) + val[i++] = negate ? 0 : -1; + return i; + } + while (i < end / HOST_BITS_PER_WIDE_INT) /* 1111111 */ val[i++] = negate ? 0 : -1; @@ -853,7 +860,7 @@ wi::shifted_mask (HOST_WIDE_INT *val, unsigned int start, unsigned int width, HOST_WIDE_INT block = (HOST_WIDE_INT_1U << shift) - 1; val[i++] = negate ? ~block : block; } - else if (end < prec) + else val[i++] = negate ? -1 : 0; return i; @@ -2583,6 +2590,10 @@ wide_int_cc_tests () run_all_wide_int_tests <widest_int> (); test_overflow (); test_round_for_mask (); + ASSERT_EQ (wi::mask (128, false, 128), + wi::shifted_mask (0, 128, false, 128)); + ASSERT_EQ (wi::mask (128, true, 128), + wi::shifted_mask (0, 128, true, 128)); } } // namespace selftest |