nir/from_ssa: Don't try to read an invalid instruction
Right now, the nir_instr_prev function function blindly looks up the previous element in the exec list and casts it to an instruction even if it's the tail sentinel. The next commit will change this to return null if it's the first instruction. Making this change first avoids getting a segfault between commits. The only reason we never noticed is that, thanks to the way things are laid out in nir_block, the casted instruction's type was never parallal_copy. Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
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@ -272,7 +272,7 @@ get_parallel_copy_at_end_of_block(nir_block *block)
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if (last_instr->type == nir_instr_type_jump)
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last_instr = nir_instr_prev(last_instr);
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if (last_instr->type == nir_instr_type_parallel_copy)
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if (last_instr && last_instr->type == nir_instr_type_parallel_copy)
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return nir_instr_as_parallel_copy(last_instr);
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else
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return NULL;
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