llvm-project

1f78f6a2 - [LV] Check Addr in getAddressAccessSCEV in terms of SCEV expressions. (#171204)

[LV] Check Addr in getAddressAccessSCEV in terms of SCEV expressions. (#171204) getAddressAccessSCEV previously had some restrictive checks that limited pointer SCEV expressions passed to TTI to GEPs with operands that must either be invariant or marked as inductions. As a consequence, the check rejected things like `GEP %base, (%iv + 1)`, while the SCEV for the GEP should be as easily analyzeable as for `GEP %base, %v`, with the only difference being the of the AddRec start adjusted by 1. This patch changes the code to use a SCEV-based check, limiting the address SCEV to be loop invariant, an affine AddRec (i.e. induction ), or an add expression of such operands or a sign-extended AddRec. This catches all existing cases getAddressAccessSCEV caught, plus additional ones like the cases mentioned above. This means we pass address SCEVs in more cases, giving the backends a better change to make informed decisions. It also unifies the decision when to use an address SCEV between the legacy and VPlan-based cost model. An illustrative example of showing the impact are the gather-cost.ll tests. Previously they were considered not profitable to vectorize because we failed to determine that %gep.src_data = getelementptr inbounds [1536 x float], ptr @src_data, i64 0, i64 %mul has a relatively small constant stride. There may be some rough edges in the cost models, where not passing pointer SCEVs hid some incorrect modeling, but those issues should be fixed in the target cost models if they surface. PR: https://github.com/llvm/llvm-project/pull/171204