[llvm] [ValueTracking] Compute known bits of and/or recurrences from start and step (PR #226164)

[Ömer Sinan Ağacan via llvm-commits]

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@@ -1899,13 +1899,33 @@ static void computeKnownBitsFromOperator(const Operator *I,
         break;
       }
 
+      // For a bitwise recurrence {Start,op,Step}, the step only applies from
+      // the second iteration on, so every fact must also hold for the start
+      // value alone.
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osa1 wrote:

This is a general fact about this whole analysis.
It should be above `matchSimpleRecurrence` call if you really want to mention it, but I think it's not necessary.

https://github.com/llvm/llvm-project/pull/226164