[PATCH] D124889: [ValueTracking] Add support to deduce a PHI node being a power of 2 if each incoming value is a power of 2.

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2058
+    }
+  }
+
----------------
Hm, I think that for recurrences, this context instruction adjustment is not necessary. I believe the reason why we need it in general for phis is that we might follow a backedge, in which case we will be working with values from a previous loop iterations. This can't happen when we're looking at Start, because it must dominate the whole loop.


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:2090
+  case Instruction::LShr:
+    return OrZero;
+  default:
----------------
Similar to the nowrap cases above, can't this (and div) use `OrZero || Q.IIQ.isExact(BO)`?


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  https://reviews.llvm.org/D124889/new/

https://reviews.llvm.org/D124889