Only the blocks that are reachable are inserted with an end_nop
instruction at the end.
When handling the Phi second pass, if the Phi has a parent block that
does not have an end_nop then it means this block is unreachable, and
thus we can ignore it, as the Phi will never come through it.
Fixes dEQP-VK.graphicsfuzz.uninit-element-cast-in-loop.
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Juan A. Suarez Romero
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