bpf: do not emit BPF non-fetching atomic instructions

When GCC finds a call to one of the __atomic_OP_fetch built-ins in
which the return value is not used it optimizes it into the
corresponding non-fetching atomic operation.  Up to now we had
definitions in gcc/config/bpf/atomic.md to implement both atomic_OP
and atomic_fetch_OP sets of insns:

  atomic_add -> aadd (aka xadd)
  atomic_and -> aand
  atomic_or  -> aor
  atomic_xor -> axor

  atomic_fetch_add -> afadd
  atomic_fetch_and -> afand
  atomic_fetch_or  -> afor
  atomic_fetch_xor -> afxor

This was not correct, because as it happens the non-fetching BPF
atomic instructions imply different memory ordering semantics than the
fetching BPF atomic instructions, and they cannot be used
interchangeably, as it would be expected.

This patch modifies config/bpf/atomic.md in order to not define the
atomic_{add,and,or,xor} insns.  This makes GCC to implement them in
terms of the corresponding fetching operations; this is less
efficient, but correct.  It also updates the expected results in the
corresponding tests, which are also updated to cover cases where the
value resulting from the __atomic_fetch_* operations is actually used.

Tested in bpf-unknown-none target in x86_64-linux-gnu host.

gcc/ChangeLog

	* config/bpf/atomic.md ("atomic_add<AMO:mode>"): Remove insn.
	("atomic_and<AMO:mode>"): Likewise
	("atomic_or<AMO:mode>"): Likewise.
	("atomic_xor<AMO:mode>"): Likewise.

gcc/testsuite/ChangeLog

	* gcc.target/bpf/atomic-op-1.c (test_used_atomic_add): New
	function.
	(test_used_atomic_sub): Likewise.
	(test_used_atomic_and): Likewise.
	(test_used_atomic_nand): Likewise.
	(test_used_atomic_or): Likewise.
	(test_used_atomic_xor): Likewise.
	* gcc.target/bpf/atomic-op-2.c (test_used_atomic_add): Likewise.
	(test_used_atomic_sub): Likewise.
	(test_used_atomic_and): Likewise.
	(test_used_atomic_nand): Likewise.
	(test_used_atomic_or): Likewise.
	(test_used_atomic_xor): Likewise.
	* gcc.target/bpf/sync-fetch-and-add.c: Expected results updated.

0 files changed, 0 insertions, 0 deletions