WIP: spirv-opt: Demote r/w output variables to private #5672
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Fix KhronosGroup#5516 Pass: eliminate dead output stores Stores to write-only output variables are safe to eliminate; however, stores to read-write output variables may be required for functional correctness. If a read-write output variable is detected, then it will be demoted to a private variable and any associated stores will not be eliminated.
jeremy-lunarg
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This look reasonable to me, but I did not look at it in detail. I'll let a code owner (someone from lunarg) do a detailed review. |
jeremy-lunarg
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Thanks @s-perron. There's one more thing I'd like to address before pushing this. |
| analysis::DefUseManager* def_use_mgr = context()->get_def_use_mgr(); | ||
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| bool is_read = false; | ||
| def_use_mgr->ForEachUser(variable, [&is_read](Instruction* user) { |
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Does this need to iterate over every user? If not, should WhileEachUser be used instead?
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This code does not address reads and writes of Output variables through OpAccessChains. So this pass is still broken for these cases. I suggest the following approach: if the Output OpVariable has an OpLoad either directly through the OpVariable or through an OpAccessChain, 1) create a Private OpVariable with the same type as the Output OpVariable and replace all uses of the Output OpVariable with the Private OpVariable; then 2) for each OpStore of the Private OpVariable, either directly through the OpVariable or through an OpAccessChain, insert a duplicate OpStore (and OpAccessChain if needed) using the original Output OpVariable. Then allow the original logic to process the Output variable and it's OpStores. |
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Fix #5516
Pass: eliminate dead output stores
Stores to write-only output variables are safe to eliminate; however, stores to read-write output variables may be required for functional correctness. If a read-write output variable is detected, then it will be demoted to a private variable and any associated stores will not be eliminated.