[PATCH] D85969: [SCEV] Model (xor (shl x, C), (-1 << C)) as (shl (xor x, -1), C)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri requested changes to this revision.
lebedev.ri added a comment.
This revision now requires changes to proceed.

Modelling this in SCEV is totally justifiable even if InstCombine knows how to fix the pattern, 
iff having this complexity actually helps. E.g. InstCombine has one-use check, so it won't fix everything.

To find that out, add a `STATISTIC()` and prove that the code actually fires on some codebase.

Marking as reviewed for now.



================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:6229-6230
+              const SCEV *NotXSCEV = getNotSCEV(getSCEV(LBO->getOperand(0)));
+              if (auto *SCEV = getShlByConstantExpr(NotXSCEV, SA, Flags))
+                return SCEV;
+            }
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Add statistic here


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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85969/new/

https://reviews.llvm.org/D85969