derive and expose address keyed NZCV flag liveness - #289
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First pass. I'd like to do a second pass looking at the algo but ran out of time today for that.
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Add ASTILiveness, which computes NZCV flag live-in/live-out per instruction address for a function by building per-address use/kill sets from the per-instruction flag-reaching-def facts and running a backward live-variable fixpoint over the CFG. Block instructions are ordered with the same lexicographic sort BasicBlock uses, which also tolerates the analysis's inlined-instruction addresses.
Add a flag-liveness map (keyed by instruction address) to ASTProvenance with the standard getter/setter, and round-trip it through serialize/deserialize alongside the other provenance facts.
Compute flag-liveness in mk_asts, alongside set_ast_provenance, so it flows through the same builder path as the other provenance facts (rather than only on the results-ast command path). The computation is auxiliary and guarded so a failure cannot abort AST generation.
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is_real_def_site excluded any "F"-prefixed def-site as "not a site in this function's CFG", which was wrong. Those instructions execute and define what they define, and their addresses are ordinary keys in fn.blocks and fn.instructions. _use_kill was therefore recording uses at those addresses while discarding their kills.
An "init" def-site means the value was defined on function entry rather than by an instruction. For a registers that is ordinary and an incoming parameter is defined exactly there. This is not normal for a flag because the ABI leaves NZCV undefined on entry to a function.
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The tail commits were merged in the stacked branch in PR #290, so closing this PR. |
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CodeHawk records per-instruction flag-reaching-def facts but exposes no liveness. This PR derives NZCV flag live-in/live-out for each instruction address and attaches it to the function's provenance, so a consumer can tell whether a flag set by a compare is still needed past a given point.
This metadata is used by the the patcher's predicated-if in-place patching mechanism as a safety check to confirm NZCV are dead at the region exit before replacing a compare.