JIT: Avoid unnecessary write backs during physical promotion #112949
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Physical promotion sometimes needs to insert writebacks to restore the struct local from a promoted replacement field. This is required if the field is more up to date and we end up in a situation where we need to represent something using the struct local. Before this change the handling of this was quite simplistic. We assumed that the replacement was more up to date than the struct local at the beginning of every basic block. This PR instead adds flow sensitive tracking to propagate this information across basic blocks. We now only consider the replacement local to be more up to date than the struct local if it was actually written in any of the predecessors.
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Physical promotion sometimes needs to insert writebacks to restore the struct local from a promoted replacement field. This is required if the field is more up to date and we end up in a situation where we need to represent something using the struct local.
Before this change the handling of this was quite simplistic. We assumed that the replacement was more up to date than the struct local at the beginning of every basic block.
This PR instead adds flow sensitive tracking to propagate this information across basic blocks. We now only consider the replacement local to be more up to date than the struct local if it was actually written in any of the predecessors.
This fixes some regressions I saw in #112740