[Bug tree-optimization/106513] New: bswap is incorrectly generated
kristerw at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Wed Aug 3 11:56:49 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106513
Bug ID: 106513
Summary: bswap is incorrectly generated
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: kristerw at gcc dot gnu.org
Target Milestone: ---
GCC may incorrectly generate bswap instructions for code not doing a correct
swap. This can be seen by running the function from testsuite/gcc.dg/pr40501.c
as
typedef long int int64_t;
__attribute__((noinline)) int64_t
swap64 (int64_t n)
{
return (((n & (((int64_t) 0xff) )) << 56) |
((n & (((int64_t) 0xff) << 8)) << 40) |
((n & (((int64_t) 0xff) << 16)) << 24) |
((n & (((int64_t) 0xff) << 24)) << 8) |
((n & (((int64_t) 0xff) << 32)) >> 8) |
((n & (((int64_t) 0xff) << 40)) >> 24) |
((n & (((int64_t) 0xff) << 48)) >> 40) |
((n & (((int64_t) 0xff) << 56)) >> 56));
}
int main (void)
{
volatile int64_t n = 0x8000000000000000l;
if (swap64(n) != 0xffffffffffffff80l)
__builtin_abort ();
return 0;
}
This fails at -Os and higher optimization levels.
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