slot2ssa: consider liveness when inserting PiNodes
#51406
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maleadt
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Sep 20, 2023
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Not familiar with the code, but it does seem to fix both the MWE and BioStockholm.jl, so SGTM.
PhiNodes are not required to be inserted for blocks where a variable is dead, so we can end up with "incoming" values to the block that aren't valid dominators. This is benign since (un-)liveness means that these values should never end up in the IR, but if we blindly insert a PiNode, that can create a usage "out of thin air" that references a non-dominating value and produces invalid IR. This commit resolves this by saving the liveness information from PhiNode insertion and checking against it for PiNode insertion.
aviatesk
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LGTM.
@nanosoldier runbenchmarks("inference", vs=":master")
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If we blindly insert a
PiNodewithout considering liveness, that can create a usage "out of thin air" that ourPhiNodeinsertion did not account for. The result is a reference to a non-dominating value, producing invalid IR.Resolves #51144.
p.s. I'd like to re-factor this code in the future to walk the dominator tree so that we can re-use
PiNode's across basic blocks and avoid some of these temporaries, but this is good as a quick fix.