34 lines
2.2 KiB
Plaintext
34 lines
2.2 KiB
Plaintext
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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- Use gcc 16 callback in build_component_ref to replace relevant offfsetofs with __spslr_offsetof(uid) calls
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- Maintain mapping from uid to type and member information
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- At early RTL, find calls and replace them with UNSPEC RTL mov instructions of constants
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- Doing it late would most certainly litter rax (return of call)
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- Doing it late would also cause surrounding code to deal with clobbering caused by call!
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- At very late RTL, find UNSPECs, replace them with constants and add asm labels
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- To begin with, this causes one move per offsetof
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- Later, add DIY constant folding -> patcher executes byte code program produced by postprocessor
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- Patcher program also handles instructions like SET_PERM(RWX, base, page count)
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- Current operand values and arbitrary number of member offsets can be used in new operand value compuation
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- Patcher is just a byte code interpreter
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OLD Approach 1:
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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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OLD Approach 2:
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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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