Docs updated
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General:
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- Use custom __builtin_offsetof definition to preserve the call until lower gimple
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Approach:
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OLD Approach:
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- At the very last point of gimple (after gimple optimizations), recognize accesses
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- Build a mapping of statement location (multiple statements share) to a semantic graph (or tree)
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- Right after expansion to RTL, pattern match set of RTL instructions with same location to graph
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- Add notes (persistent over RTL transformations) to any RTL instruction that is relevant
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- After all RTL optimizations, add assembly labels before relevant RTL instructions (identified by notes)
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- Might need an additional early pass to prevent COMPONENT_REFs to constant/static stuff from being folded early
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Approach:
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- At the very first point of gimple (before optimizations), replace COMPONENT_REFs of relevant structs
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- Turn them into calls of __spslr_component_ref(base (new ssa stmt), type uid, member uid)
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- Make sure the return type is matching that of the COMPONENT_REF (member type)
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- Let those calls get lowered all the way into UNOPTIMIZED RTL
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- Replace calls by inserting original constants and attaching notes
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- Let RTL optimizations do their job with those many separate constants
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- At the very end of RTL, recognize member offsets by notes and add assembly labels
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- MIGHT require some logic to trace notes through RTL optimizations (which operand?, combined how?)
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@ -18,3 +18,4 @@ Constant foldable expressions, e.g. "size_t myOffset = ((size_t)&((struct task_s
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-> gcc folds those expressions before PLUGIN_FINISH_PARSE_FUNCTION
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-> any recoverability of COMPONENT_REF is impossible
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-> requires gcc patch (fairly small one though)
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-> fold_offsetof in the C frontend is responsible
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