[PATCH] D71539: [SCEV] Look through trivial PHIs.

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev accepted this revision.
mkazantsev added a comment.
This revision is now accepted and ready to land.

Looks good (with nits).



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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:3692
 }
-
 /// Return an existing SCEV if it exists, otherwise analyze the expression and
----------------
Nit


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:3717
       // If V is GetElementPtrInst, don't save Stripped -> {V, offset}
       // because it may generate add/sub instead of GEP in SCEV expansion.
       if (Offset != nullptr && !isa<SCEVUnknown>(Stripped) &&
----------------
Does this comment need explanation about what do we do for Phis?


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:5120
 
-  // If the PHI has a single incoming value, follow that value, unless the
-  // PHI's incoming blocks are in a different loop, in which case doing so
-  // risks breaking LCSSA form. Instcombine would normally zap these, but
-  // it doesn't have DominatorTree information, so it may miss cases.
   if (Value *V = SimplifyInstruction(PN, {getDataLayout(), &TLI, &DT, &AC}))
+    return getSCEV(V);
----------------
`assert(LI.replacementPreservesLCSSAForm(PN, V))`


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