https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126625
Bug ID: 126625
Summary: hwint.cc reflect_hwi () should use
__builtin_bitreverse64 if supported.
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: kaelfandrew at gmail dot com
Target Milestone: ---
In gcc/hwint.cc, reflect_hwi () uses a naive approach to emulate
__builtin_bitreverse64 ().
But since r17-523, __builtin_bitreverse64 is now available and reflect_hwi can
be:
```
unsigned HOST_WIDE_INT
reflect_hwi (unsigned HOST_WIDE_INT value, unsigned bitwidth)
{
unsigned HOST_WIDE_INT reflected_value = 0;
#if GCC_VERSION >= 17000
if (bitwidth == 0
|| bitwidth > 64)
return 0;
reflected_value = __builtin_bitreverse64 (value) >> (64 - bitwidth);
#else
/* Loop through each bit in the specified BITWIDTH. */
for (size_t i = 0; i < bitwidth; i++)
{
reflected_value <<= 1;
/* Add the least significant bit of the current value to the
reflected value. */
reflected_value |= (value & 1);
value >>= 1;
}
#endif
return reflected_value;
}
```
