[PATCH] D89149: [SelectionDAG] Fix alias checking with potential later stack reuse

[Nirav Dave via Phabricator via llvm-commits]

niravd added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp:116
-  // can infer there is no alias.
-  if (auto *A = dyn_cast<FrameIndexSDNode>(BasePtr0.getBase()))
-    if (auto *B = dyn_cast<FrameIndexSDNode>(BasePtr1.getBase())) {
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Removing this would be a bit of a shame as it has some nice improvements in other backends. (Also, is it only showing up in BPF or can you replicate this on X86/ARM?

I don't have the best knowledge on FrameInfo structures, so we should probably loop in someone who gets that better, but we should see if we can extract disjointed information out of the frame info. 

At the very least, we should be able to retain that they can't alias if exactly one is fixed. However, the vast majority of improvements from this was catching disjointness of two separate allocations to see if we can keep this. 








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Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp:130
+
+  if ((IdxCheck || (IsFI0 != IsFI1) || (IsGV0 != IsGV1) || (IsCV0 != IsCV1)) &&
       (IsFI0 || IsGV0 || IsCV0) && (IsFI1 || IsGV1 || IsCV1)) {
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Can you change this so we check the two Index value match no matter what if we show non-aliasing? We really should check the both base and Index if we're going to show non-aliasing.

if (((BasePtr0.getIndex() == BasePtr1.getIndex()) &&
     ((IsFI0 != IsFI1) || (IsGV0 != IsGV1) || (IsCV0 != IsCV1)) &&


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  https://reviews.llvm.org/D89149/new/

https://reviews.llvm.org/D89149