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authorJakub Jelinek <jakub@redhat.com>2022-07-01 11:17:41 +0200
committerJakub Jelinek <jakub@redhat.com>2022-07-30 11:34:30 +0200
commit527dccb33e54ffe49fb1507fc4539968f48a9d12 (patch)
tree245d3cca08c87ca257368df0b0ff2566f55c8fde /MAINTAINERS
parent2339ee2c89af80270840e04fc0906acea765489f (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)
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