[PATCH] D82715: [LVI][CVP] Handle (x | y) < C style conditions

Wed Jul 1 09:42:40 PDT 2020

spatel added inline comments.

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Comment at: llvm/lib/Analysis/LazyValueInfo.cpp:1106

+  // If (x | y) < C, then (x < C) && (y < C).
+  if (match(LHS, m_c_Or(m_Specific(Val), m_Value())) &&
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nikic wrote:
> spatel wrote:
> > These transforms only work when C is a low-bit mask or power-of-2 (depending on predicate)?
> > https://alive2.llvm.org/ce/z/pmF7PF
> Ah, to be clear, this is not an equivalence, only an implication. If `(x | y) < 9` we know that both `x < 9` and `y < 9`, but if we know that `x < 9` and `y < 9`, it does not follow that `(x | y) < 9` (which is what the alive proof is showing). Here, we only care about implication in one direction.
Modify/add tests with arbitrary constants to make that more obvious then? I missed the relationship because we're using '7' in all cases.

Repository:
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  https://reviews.llvm.org/D82715/new/

https://reviews.llvm.org/D82715