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| author | Richard Sandiford <richard.sandiford@arm.com> | 2018-07-25 08:41:35 +0000 |
|---|---|---|
| committer | Richard Sandiford <rsandifo@gcc.gnu.org> | 2018-07-25 08:41:35 +0000 |
| commit | e8dce850a7ffcffff4690f62f85e0ed4ede4d82a (patch) | |
| tree | 9f721d74a8a88c9af1612dc3c67cdb9f9aa32b6b /gcc/hwint.c | |
| parent | de6c8d7f72822c579ff07382d74ecb5c142a49b2 (diff) | |
| download | gcc-e8dce850a7ffcffff4690f62f85e0ed4ede4d82a.zip gcc-e8dce850a7ffcffff4690f62f85e0ed4ede4d82a.tar.gz gcc-e8dce850a7ffcffff4690f62f85e0ed4ede4d82a.tar.bz2 | |
Fix ceil_log2(0) (PR 86644)
This PR shows a pathological case in which we try SLP vectorisation on
dead code. We record that 0 bits of the result are enough to satisfy
all users (which is true), and that led to precision being 0 in:
static unsigned int
vect_element_precision (unsigned int precision)
{
precision = 1 << ceil_log2 (precision);
return MAX (precision, BITS_PER_UNIT);
}
ceil_log2 (0) returned 64 rather than 0, leading to 1 << 64, which is UB.
2018-07-25 Richard Sandiford <richard.sandiford@arm.com>
gcc/
* hwint.c (ceil_log2): Fix comment. Return 0 for 0.
From-SVN: r262961
Diffstat (limited to 'gcc/hwint.c')
| -rw-r--r-- | gcc/hwint.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/gcc/hwint.c b/gcc/hwint.c index 7258df7..b10b5e4 100644 --- a/gcc/hwint.c +++ b/gcc/hwint.c @@ -60,12 +60,12 @@ floor_log2 (unsigned HOST_WIDE_INT x) return t; } -/* Given X, an unsigned number, return the largest Y such that 2**Y >= X. */ +/* Given X, an unsigned number, return the least Y such that 2**Y >= X. */ int ceil_log2 (unsigned HOST_WIDE_INT x) { - return floor_log2 (x - 1) + 1; + return x == 0 ? 0 : floor_log2 (x - 1) + 1; } /* Return the logarithm of X, base 2, considering X unsigned, |