compiler/nir: Add support for lowering stores with nir_lower_instruction
The function is very convenient for lowering any type of instruction that can be easily filtered, but so far instructions that didn't return a value were silently ignored.
Fix this by
- not requiring a return value in the instruction,
- add a new special return value from the lowering implementation function to indicated that an instruction that doesn't have a return value must be removed, and
- don't try to collect and replace uses in this case.
@jekstrand @anholt
Edited by Gert Wollny