[nvptx] Use _ as destination operand of atom.exch
We currently generate this code for an atomic store:
...
.reg.u32 %r21;
atom.exch.b32 %r21,[%r22],%r23;
...
where %r21 is set but unused.
Use the ptx bit bucket operand '_' instead, such that we have:
...
atom.exch.b32 _,[%r22],%r23;
...
[ Note that the same problem still occurs for this code:
...
void atomic_store (int *ptr, int val) {
__atomic_exchange_n (ptr, val, MEMMODEL_RELAXED);
}
... ]
Tested on nvptx.
gcc/ChangeLog:
2022-02-19 Tom de Vries <tdevries@suse.de>
* config/nvptx/nvptx.cc (nvptx_reorg_uniform_simt): Handle SET insn.
* config/nvptx/nvptx.md
(define_insn "nvptx_atomic_store<mode>"): Rename to ...
(define_insn "nvptx_atomic_store_sm70<mode>"): This.
(define_insn "nvptx_atomic_store<mode>"): New define_insn.
(define_expand "atomic_store<mode>"): Handle rename. Use
nvptx_atomic_store instead of atomic_exchange.
gcc/testsuite/ChangeLog:
2022-02-19 Tom de Vries <tdevries@suse.de>
* gcc.target/nvptx/atomic-store-1.c: Update.