// mapaccess2* returns a typed bool, but due to spec changes,
	// the boolean result of i.(T) is now untyped so we make it the
	// same type as the variable on the lhs.
	if ok := n.Lhs[1]; !ir.IsBlank(ok) && ok.Type().IsBoolean() {
		call.Type().Field(1).Type = ok.Type()
	}
	n.Rhs = []ir.Node{call}
	n.SetOp(ir.OAS2FUNC)

	// don't generate a = *var if a is _
	if ir.IsBlank(a) {
		return walkExpr(typecheck.Stmt(n), init)
	}

		// assert(pred) causes a typechecker error if pred is false.
		// The result of assert is the value of pred if there is no error.
		// Note: assert is only available in self-test mode.
		if x.mode != constant_ || !isBoolean(x.typ) {
			check.errorf(x, Test, invalidArg+"%s is not a boolean constant", x)
			return
		}
		if x.val.Kind() != constant.Bool {
			check.errorf(x, Test, "internal error: value of %s should be a boolean constant", x)

		// assert(pred) causes a typechecker error if pred is false.
		// The result of assert is the value of pred if there is no error.
		// Note: assert is only available in self-test mode.
		if x.mode != constant_ || !isBoolean(x.typ) {
			check.errorf(x, Test, invalidArg+"%s is not a boolean constant", x)
			return
		}
		if x.val.Kind() != constant.Bool {
			check.errorf(x, Test, "internal error: value of %s should be a boolean constant", x)

		assert(cb.Recv() == nil)
		switch {
		case cb.Params().Len() > 2:
			return bad("func must be func(yield func(...) bool): yield func has too many parameters")
		case cb.Results().Len() != 1 || !isBoolean(cb.Results().At(0).Type()):
			return bad("func must be func(yield func(...) bool): yield func does not return bool")
		}
		if cb.Params().Len() >= 1 {
			key = cb.Params().At(0).Type()
		}

		assert(cb.Recv() == nil)
		switch {
		case cb.Params().Len() > 2:
			return bad("func must be func(yield func(...) bool): yield func has too many parameters")
		case cb.Results().Len() != 1 || !isBoolean(cb.Results().At(0).Type()):
			return bad("func must be func(yield func(...) bool): yield func does not return bool")
		}
		if cb.Params().Len() >= 1 {
			key = cb.Params().At(0).Type()
		}

(Neq64  x y) => (Not (Eq64  x y))
(Neq32  x y) => (Not (Eq32  x y))
(Neq16  x y) => (Not (Eq16  x y))
(Neq8   x y) => (Not (Eq8   x y))
(Neq(64|32)F ...) => (FNE(D|S) ...)

// Loads
(Load <t> ptr mem) &&  t.IsBoolean()                   => (MOVBUload ptr mem)
(Load <t> ptr mem) && ( is8BitInt(t) &&  t.IsSigned()) => (MOVBload  ptr mem)
(Load <t> ptr mem) && ( is8BitInt(t) && !t.IsSigned()) => (MOVBUload ptr mem)