// LoweredWB invokes runtime.gcWriteBarrier{auxint}. arg0=mem, auxint=# of buffer entries needed.
		// It saves all GP registers if necessary, but may clobber others.
		// Returns a pointer to a write barrier buffer in R11.

(AtomicAnd(64|32|8)Variant     ...) => (LoweredAtomicAnd(64|32|8)Variant     ...)
(AtomicOr(64|32|8)Variant      ...) => (LoweredAtomicOr(64|32|8)Variant      ...)

// Write barrier.
(WB ...) => (LoweredWB ...)

// Publication barrier (0xe is ST option)
(PubBarrier mem) => (DMB [0xe] mem)

(PanicBounds [kind] x y mem) && boundsABI(kind) == 0 => (LoweredPanicBoundsA [kind] x y mem)