Nikita Popov 32cd18975d [GVN] Look through select/phi when determining underlying object (#99509) ...

This addresses an optimization regression in Rust we have observed after
https://github.com/llvm/llvm-project/pull/82458. We now only perform
pointer replacement if they have the same underlying object. However,
getUnderlyingObject() by default only looks through linear chains, not
selects/phis. In particular, this means that we miss cases involving
involving pointer induction variables.

This patch fixes this by introducing a new helper
getUnderlyingObjectAggressive() which basically does what
getUnderlyingObjects() does, just specialized to the case where we must
arrive at a single underlying object in the end, and with a limit on the
number of inspected values.

Doing this more expensive underlying object check has no measurable
compile-time impact on CTMark.

2024-07-22 16:22:01 +02:00

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