[PATCH] D77804: [DAG] Enable ISD::SRL SimplifyMultipleUseDemandedBits handling inside SimplifyDemandedBits (WIP)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:6871
+
+    // (or (and X, C1), (and (or X, Y), C2)) -> (or (and X, C1|C2), (and Y, C2))
+    if (N1.getOpcode() == ISD::AND) {
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spatel wrote:
> spatel wrote:
> > This could be a preliminary patch. I don't think we'd get that in IR either (even without extra uses):
> > https://alive2.llvm.org/ce/z/g61VRe
> If I'm reading the SystemZ debug spew correctly, we should have gotten this transform to fire twice, so it would do this:
> https://alive2.llvm.org/ce/z/tUsepa
> ...but we miss it because we don't revisit the last 'or' node? Is that what D127115 would solve?
I've confirmed that D127115 solves the SystemZ fun3 regression but not fun2


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  https://reviews.llvm.org/D77804/new/

https://reviews.llvm.org/D77804