[PATCH] D129753: [SCEV] Prove condition invariance via context

[Artur Pilipenko via Phabricator via llvm-commits]

apilipenko added inline comments.


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:10815-10829
+    assert(ArLHS->hasNoUnsignedWrap() && "Is a requirement of monotonicity!");
+    // If we can prove that ArLHS <s RHS, and RHS >=s 0, and we know that ArLHS
+    // does not cross zero, there are two options:
+    // - ArLHS is always negative. It means that ArLHS <u RHS is always false;
+    // - ArLHS is always non-negative. It means that
+    //     ArLHS <s RHS <=> ArLHS <u RHS.
+    //   We are guarded by ArLHS <s RHS, so unsigned condition is trivially
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Suggested slight rewording of the reasoning and restructuring of the code. 


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Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:10824
+    // All together it means that ArLHS <u RHS <=> Start(ArLHS) >=s 0.
+    // We can strenthen this to Start(ArLHS <u RHS).
+    auto SignFlippedPred = ICmpInst::getFlippedSignednessPredicate(Pred);
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Why don't you use Start(ArLHS) >=s 0 as the resulting invariant condition?


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  https://reviews.llvm.org/D129753/new/

https://reviews.llvm.org/D129753