[llvm] [VPlan] Optimize FindLast of (binop %IV, live-in) by sinking. (PR #183911)

[via llvm-commits]

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ayalz wrote:

Sounds right, a sort of closed-SSA oriented preparation for widening.

May be good to (a) first canonicalize to obtain raw reduction forms including sinking whenever possible; then (b) perform mandatory-legal processing w/o sentinels; then (c) apply potentially multiple alternative cost-based optimizations including unsinking and/or sentinelization.

https://github.com/llvm/llvm-project/pull/183911