Add reduction string test for ctc_loss.

[ghstack-poisoned]

test/test_nn.py

@@ -9769,6 +9769,12 @@ def v(fn):
             v(lambda: F.margin_ranking_loss(input, input, input.sign(), reduction=reduction))
             v(lambda: F.cosine_embedding_loss(input, input, input[:, 0].sign(), reduction=reduction))
 
+            log_probs = torch.randn(50, 16, 20, requires_grad=True, device=device).log_softmax(2)
+            targets = torch.randint(1, 20, (16, 30), dtype=torch.long, device=device)
+            input_lengths = torch.full((16,), 50, dtype=torch.long, device=device)
+            target_lengths = torch.randint(10, 30, (16,), dtype=torch.long, device=device)
+            v(lambda: F.ctc_loss(log_probs, targets, input_lengths, target_lengths, reduction=reduction))
+
             # FIXME: should we allow derivatives on these?
             v(lambda: F.binary_cross_entropy(torch.sigmoid(input), input.detach(), reduction=reduction))
             v(lambda: F.soft_margin_loss(input, input.sign().detach(), reduction=reduction))