[nvptx] Use bit-bucket operand for atom insns
For an atomic fetch operation that doesn't use the result:
...
__atomic_fetch_add (p64, v64, MEMMODEL_RELAXED);
...
we currently emit:
...
atom.add.u64 %r26, [%r25], %r27;
...
Detect the REG_UNUSED reg-note for %r26, and emit instead:
...
atom.add.u64 _, [%r25], %r27;
...
Likewise for all atom insns.
Tested on nvptx.
gcc/ChangeLog:
2022-03-07 Tom de Vries <tdevries@suse.de>
PR target/104815
* config/nvptx/nvptx.cc (nvptx_print_operand): Handle 'x' operand
modifier.
* config/nvptx/nvptx.md: Use %x0 destination operand in atom insns.
gcc/testsuite/ChangeLog:
2022-03-07 Tom de Vries <tdevries@suse.de>
PR target/104815
* gcc.target/nvptx/atomic-bit-bucket-dest.c: New test.