MESA: nir_lower_phis_to_regs_block: Assertion `src->src.is_ssa' failed.

[Jack-Clark]

Running amber -t spv1.3 -v 1.1 nir_lower_phis_to_regs_block.amber gives the following error:

amber: ../src/compiler/nir/nir_from_ssa.c:1009: nir_lower_phis_to_regs_block: Assertion `src->src.is_ssa' failed.
Aborted (core dumped)

I can reproduce this on the 22.0.1 release and main (9f44a264623). Here is the CFG:

nir_lower_phis_to_regs_block.tar.gz