[PATCH] D73181: [SCEV] Do not use backedge SCEV of PHI if its input is another PHI

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:8246
+            const SCEV *OnBackedge = getSCEV(BackedgeVal);
+            if (!isa<PHINode>(BackedgeVal) &&
+                IsAvailableOnEntry(LI, DT, OnBackedge, PN->getParent()))
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Your check is overprotective. If `BackedgeVal` is a Phi from another loop than PN's (e.g. outer loop or some other loop going before it), it is OK to use it as exit value. The problem only happens if `PN->getLoop() == BackedgeVal->getLoop()`, am I correct?


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Comment at: llvm/test/Analysis/ScalarEvolution/pr44605.ll:46
+  %local_3_31 = mul i32 %local_4_5.pn, %.udiv
+  %0 = mul i32 %local_7_3, %.udiv
+  %1 = sub i32 %0, %local_3_4
----------------
Does the test really need all these computations inside? It's tad too much code, not clear what of it is important. If you can reduce the test please do.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D73181/new/

https://reviews.llvm.org/D73181